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Class 5 Antiarrhythmic Drugs

Class 5 antiarrhythmic drugs are a miscellaneous group of medications that do not belong to a traditional class of antiarrhythmics. These drugs have varied mechanisms of action and uses. The medications in this class are digoxin Digoxin A cardiotonic glycoside obtained mainly from digitalis lanata; it consists of three sugars and the aglycone digoxigenin. Digoxin has positive inotropic and negative chronotropic activity. It is used to control ventricular rate in atrial fibrillation and in the management of congestive heart failure with atrial fibrillation. Its use in congestive heart failure and sinus rhythm is less certain. The margin between toxic and therapeutic doses is small. Cardiac Glycosides, adenosine, Mg sulfate, and atropine Atropine An alkaloid, originally from atropa belladonna, but found in other plants, mainly solanaceae. Hyoscyamine is the 3(s)-endo isomer of atropine. Anticholinergic Drugs. Digoxin Digoxin A cardiotonic glycoside obtained mainly from digitalis lanata; it consists of three sugars and the aglycone digoxigenin. Digoxin has positive inotropic and negative chronotropic activity. It is used to control ventricular rate in atrial fibrillation and in the management of congestive heart failure with atrial fibrillation. Its use in congestive heart failure and sinus rhythm is less certain. The margin between toxic and therapeutic doses is small. Cardiac Glycosides’s antiarrhythmic effect comes from increased vagal tone and direct action on the atrioventricular node Atrioventricular node A small nodular mass of specialized muscle fibers located in the interatrial septum near the opening of the coronary sinus. It gives rise to the atrioventricular bundle of the conduction system of the heart. Heart: Anatomy ( AVN Avn Hip Fractures), resulting in decreased AVN Avn Hip Fractures conduction and sinoatrial (SA) automaticity. Digoxin Digoxin A cardiotonic glycoside obtained mainly from digitalis lanata; it consists of three sugars and the aglycone digoxigenin. Digoxin has positive inotropic and negative chronotropic activity. It is used to control ventricular rate in atrial fibrillation and in the management of congestive heart failure with atrial fibrillation. Its use in congestive heart failure and sinus rhythm is less certain. The margin between toxic and therapeutic doses is small. Cardiac Glycosides can be used for atrial fibrillation Atrial fibrillation Atrial fibrillation (AF or Afib) is a supraventricular tachyarrhythmia and the most common kind of arrhythmia. It is caused by rapid, uncontrolled atrial contractions and uncoordinated ventricular responses. Atrial Fibrillation ( AFib Afib Atrial fibrillation (AF or Afib) is a supraventricular tachyarrhythmia and the most common kind of arrhythmia. It is caused by rapid, uncontrolled atrial contractions and uncoordinated ventricular responses. Atrial Fibrillation), atrial flutter Atrial flutter Atrial flutter is a regular supraventricular tachycardia characterized by an atrial heart rate between 240/min and 340/min (typically 300/min), atrioventricular (AV) node conduction block, and a "sawtooth" pattern on an electrocardiogram (ECG). Atrial Flutter (AFL), and supraventricular tachycardia Tachycardia Abnormally rapid heartbeat, usually with a heart rate above 100 beats per minute for adults. Tachycardia accompanied by disturbance in the cardiac depolarization (cardiac arrhythmia) is called tachyarrhythmia. Sepsis in Children ( SVT SVT Supraventricular tachycardias are related disorders in which the elevation in heart rate is driven by pathophysiology in the atria. This group falls under the larger umbrella of tachyarrhythmias and includes paroxysmal supraventricular tachycardias (PSVTs), ventricular pre-excitation syndromes (i.e. Wolff-Parkinson-White syndrome), atrial flutter, multifocal atrial tachycardia, and atrial fibrillation. Supraventricular Tachycardias). Adenosine works on purinergic receptors Receptors Receptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell. Receptors to cause hyperpolarization Hyperpolarization Membrane Potential, which causes decreased AVN Avn Hip Fractures velocity and increased refractoriness, making it a good choice for cardioversion Cardioversion Atrial Fibrillation of SVT SVT Supraventricular tachycardias are related disorders in which the elevation in heart rate is driven by pathophysiology in the atria. This group falls under the larger umbrella of tachyarrhythmias and includes paroxysmal supraventricular tachycardias (PSVTs), ventricular pre-excitation syndromes (i.e. Wolff-Parkinson-White syndrome), atrial flutter, multifocal atrial tachycardia, and atrial fibrillation. Supraventricular Tachycardias. Magnesium Magnesium A metallic element that has the atomic symbol mg, atomic number 12, and atomic weight 24. 31. It is important for the activity of many enzymes, especially those involved in oxidative phosphorylation. Electrolytes’s mechanism of action is not well understood, but it does interact with multiple ion transport mechanisms and is helpful for patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with QT prolongation and torsades de pointes Torsades de pointes A malignant form of polymorphic ventricular tachycardia that is characterized by heart rate between 200 and 250 beats per minute, and QRS complexes with changing amplitude and twisting of the points. The term also describes the syndrome of tachycardia with prolonged ventricular repolarization, long qt intervals exceeding 500 milliseconds or bradycardia. Torsades de pointes may be self-limited or may progress to ventricular fibrillation. Ventricular Tachycardia. Finally, atropine Atropine An alkaloid, originally from atropa belladonna, but found in other plants, mainly solanaceae. Hyoscyamine is the 3(s)-endo isomer of atropine. Anticholinergic Drugs antagonizes muscarinic receptors Receptors Receptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell. Receptors and blocks vagal effects on the heart, making it useful in symptomatic and unstable bradyarrhythmias Bradyarrhythmias Bradyarrhythmia is a rhythm in which the heart rate is less than 60/min. Bradyarrhythmia can be physiologic, without symptoms or hemodynamic change. Pathologic bradyarrhythmia results in reduced cardiac output and hemodynamic instability causing syncope, dizziness, or dyspnea. Bradyarrhythmias.

Last updated: Mar 14, 2022

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Overview

Vaughan-Williams classification

This is the most commonly used classifications for antiarrhythmic drugs. There are 5 classes based on the drug class’s general effect (mechanism of action):

  • Class 1: sodium channel blockers Sodium Channel Blockers A class of drugs that act by inhibition of sodium influx through cell membranes. Blockade of sodium channels slows the rate and amplitude of initial rapid depolarization, reduces cell excitability, and reduces conduction velocity. Myotonic Dystrophies (divided into 3 subgroups)
  • Class 2: beta-blockers Beta-blockers Drugs that bind to but do not activate beta-adrenergic receptors thereby blocking the actions of beta-adrenergic agonists. Adrenergic beta-antagonists are used for treatment of hypertension, cardiac arrhythmias, angina pectoris, glaucoma, migraine headaches, and anxiety. Class 2 Antiarrhythmic Drugs (Beta Blockers)
  • Class 3: potassium Potassium An element in the alkali group of metals with an atomic symbol k, atomic number 19, and atomic weight 39. 10. It is the chief cation in the intracellular fluid of muscle and other cells. Potassium ion is a strong electrolyte that plays a significant role in the regulation of fluid volume and maintenance of the water-electrolyte balance. Hyperkalemia channel blockers
  • Class 4: calcium channel blockers Calcium Channel Blockers Calcium channel blockers (CCBs) are a class of medications that inhibit voltage-dependent L-type calcium channels of cardiac and vascular smooth muscle cells. The inhibition of these channels produces vasodilation and myocardial depression. There are 2 major classes of CCBs: dihydropyridines and non-dihydropyridines. Class 4 Antiarrhythmic Drugs (Calcium Channel Blockers) ( CCBs CCBs Calcium channel blockers (CCBS) are a class of medications that inhibit voltage-dependent L-type calcium channels of cardiac and vascular smooth muscle cells. The inhibition of these channels produces vasodilation and myocardial depression. There are 2 major classes of CCBS: dihydropyridines and non-dihydropyridines. Class 4 Antiarrhythmic Drugs (Calcium Channel Blockers))
  • Class 5: miscellaneous agents that cannot be categorized into the above groups
    • They have no common mechanism of action.
    • Includes: 
      • Digoxin Digoxin A cardiotonic glycoside obtained mainly from digitalis lanata; it consists of three sugars and the aglycone digoxigenin. Digoxin has positive inotropic and negative chronotropic activity. It is used to control ventricular rate in atrial fibrillation and in the management of congestive heart failure with atrial fibrillation. Its use in congestive heart failure and sinus rhythm is less certain. The margin between toxic and therapeutic doses is small. Cardiac Glycosides 
      • Adenosine 
      • Magnesium sulfate Magnesium Sulfate A small colorless crystal used as an anticonvulsant, a cathartic, and an electrolyte replenisher in the treatment of pre-eclampsia and eclampsia. It causes direct inhibition of action potentials in myometrial muscle cells. Excitation and contraction are uncoupled, which decreases the frequency and force of contractions. Laxatives
      • Atropine Atropine An alkaloid, originally from atropa belladonna, but found in other plants, mainly solanaceae. Hyoscyamine is the 3(s)-endo isomer of atropine. Anticholinergic Drugs

Digoxin

Mechanism of action

  • ↑ Vagal tone and direct action on the atrioventricular node Atrioventricular node A small nodular mass of specialized muscle fibers located in the interatrial septum near the opening of the coronary sinus. It gives rise to the atrioventricular bundle of the conduction system of the heart. Heart: Anatomy ( AVN Avn Hip Fractures): 
    • ↑ Refractory period → ↓ conduction velocity in the AVN Avn Hip Fractures
    • ↓ Sinoatrial (SA) node automaticity
    • Effect: ↓ ventricular rate in the setting of rapid supraventricular arrhythmias
  • Reversibly inhibits the Na/K-ATPase of myocytes Myocytes Mature contractile cells, commonly known as myocytes, that form one of three kinds of muscle. The three types of muscle cells are skeletal, cardiac, and smooth. They are derived from embryonic (precursor) muscle cells called myoblasts. Muscle Tissue: Histology, resulting in:
    • ↑ Intracellular Na → ↓ Na-calcium ( Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)) antiporter Antiporter Membrane transporters that co-transport two or more dissimilar molecules in the opposite direction across a membrane. Usually the transport of one ion or molecule is against its electrochemical gradient and is ‘powered’ by the movement of another ion or molecule with its electrochemical gradient. The Cell: Cell Membrane exchange → ↓ Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts) efflux 
    • ↑ intracellular Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts) → ↑ Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts) binding to contractile proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis → ↑ myocardial contractility 
  • May cause characteristic changes to a resting ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG) (“digitalis effect”): 
Ecg typical “scooped” st-depression resulting from digoxin use

Typical “scooped” ST-segment depression resulting from digoxin Digoxin A cardiotonic glycoside obtained mainly from digitalis lanata; it consists of three sugars and the aglycone digoxigenin. Digoxin has positive inotropic and negative chronotropic activity. It is used to control ventricular rate in atrial fibrillation and in the management of congestive heart failure with atrial fibrillation. Its use in congestive heart failure and sinus rhythm is less certain. The margin between toxic and therapeutic doses is small. Cardiac Glycosides use

Image: “Typical for digoxin Digoxin A cardiotonic glycoside obtained mainly from digitalis lanata; it consists of three sugars and the aglycone digoxigenin. Digoxin has positive inotropic and negative chronotropic activity. It is used to control ventricular rate in atrial fibrillation and in the management of congestive heart failure with atrial fibrillation. Its use in congestive heart failure and sinus rhythm is less certain. The margin between toxic and therapeutic doses is small. Cardiac Glycosides intoxication is the oddly shaped ST-depression” by I.A.C. van der Bilt, MD. License: CC BY-NC-SA 3.0

Pharmacokinetics

  • Absorption Absorption Absorption involves the uptake of nutrient molecules and their transfer from the lumen of the GI tract across the enterocytes and into the interstitial space, where they can be taken up in the venous or lymphatic circulation. Digestion and Absorption
    • Routes of administration: 
      • Oral 
      • IV
    • Passive, nonsaturable absorption Absorption Absorption involves the uptake of nutrient molecules and their transfer from the lumen of the GI tract across the enterocytes and into the interstitial space, where they can be taken up in the venous or lymphatic circulation. Digestion and Absorption in the proximal small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy
    • Food delays absorption Absorption Absorption involves the uptake of nutrient molecules and their transfer from the lumen of the GI tract across the enterocytes and into the interstitial space, where they can be taken up in the venous or lymphatic circulation. Digestion and Absorption.
  • Distribution:
    • Higher concentrations in:
      • Heart
      • Liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy
      • Kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys: Anatomy
      • Skeletal muscle
    • Crosses the blood-brain barrier Blood-brain barrier Specialized non-fenestrated tightly-joined endothelial cells with tight junctions that form a transport barrier for certain substances between the cerebral capillaries and the brain tissue. Systemic and Special Circulations and placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity
  • Metabolism and excretion: 
    • Minimal hepatic metabolism:
      • Approximately 16% of an absorbed dose is metabolized to active metabolites.
      • Does not interact with the cytochrome P450 Cytochrome P450 A superfamily of hundreds of closely related hemeproteins found throughout the phylogenetic spectrum, from animals, plants, fungi, to bacteria. They include numerous complex monooxygenases (mixed function oxygenases). In animals, these p450 enzymes serve two major functions: (1) biosynthesis of steroids, fatty acids, and bile acids; (2) metabolism of endogenous and a wide variety of exogenous substrates, such as toxins and drugs (biotransformation). They are classified, according to their sequence similarities rather than functions, into cyp gene families (>40% homology) and subfamilies (>59% homology). For example, enzymes from the cyp1, cyp2, and cyp3 gene families are responsible for most drug metabolism. Drug-induced Liver Injury system
    • Predominantly excreted in the urine Urine Liquid by-product of excretion produced in the kidneys, temporarily stored in the bladder until discharge through the urethra. Bowen Disease and Erythroplasia of Queyrat (50%–70% as an unchanged drug)

Indications

  • Arrhythmia (for HR control when other therapies are ineffective or contraindicated)
    • Atrial fibrillation Atrial fibrillation Atrial fibrillation (AF or Afib) is a supraventricular tachyarrhythmia and the most common kind of arrhythmia. It is caused by rapid, uncontrolled atrial contractions and uncoordinated ventricular responses. Atrial Fibrillation ( AFib Afib Atrial fibrillation (AF or Afib) is a supraventricular tachyarrhythmia and the most common kind of arrhythmia. It is caused by rapid, uncontrolled atrial contractions and uncoordinated ventricular responses. Atrial Fibrillation) or atrial flutter Atrial flutter Atrial flutter is a regular supraventricular tachycardia characterized by an atrial heart rate between 240/min and 340/min (typically 300/min), atrioventricular (AV) node conduction block, and a “sawtooth” pattern on an electrocardiogram (ECG). Atrial Flutter (AFL)
    • Supraventricular tachycardia Tachycardia Abnormally rapid heartbeat, usually with a heart rate above 100 beats per minute for adults. Tachycardia accompanied by disturbance in the cardiac depolarization (cardiac arrhythmia) is called tachyarrhythmia. Sepsis in Children ( SVT SVT Supraventricular tachycardias are related disorders in which the elevation in heart rate is driven by pathophysiology in the atria. This group falls under the larger umbrella of tachyarrhythmias and includes paroxysmal supraventricular tachycardias (PSVTs), ventricular pre-excitation syndromes (i.e. Wolff-Parkinson-White syndrome), atrial flutter, multifocal atrial tachycardia, and atrial fibrillation. Supraventricular Tachycardias)
  • Systolic heart failure Heart Failure A heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (ventricular dysfunction), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as myocardial infarction. Total Anomalous Pulmonary Venous Return (TAPVR)

Adverse effects

  • Cardiac Cardiac Total Anomalous Pulmonary Venous Return (TAPVR) conduction abnormalities and arrhythmia
    • Paroxysmal atrial tachycardia Paroxysmal atrial tachycardia Tachyarrhythmias (PAT)
    • Premature Premature Childbirth before 37 weeks of pregnancy (259 days from the first day of the mother’s last menstrual period, or 245 days after fertilization). Necrotizing Enterocolitis atrial or ventricular contractions
    • AV block AV block Atrioventricular (AV) block is a bradyarrhythmia caused by delay, or interruption, in the electrical conduction between the atria and the ventricles. Atrioventricular block occurs due to either anatomic or functional impairment, and is classified into 3 types. Atrioventricular block (AV block)
    • Ventricular arrhythmias
  • Other:
    • Nausea Nausea An unpleasant sensation in the stomach usually accompanied by the urge to vomit. Common causes are early pregnancy, sea and motion sickness, emotional stress, intense pain, food poisoning, and various enteroviruses. Antiemetics and vomiting Vomiting The forcible expulsion of the contents of the stomach through the mouth. Hypokalemia
    • Skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions rash Rash Rocky Mountain Spotted Fever
    • Blurred vision Vision Ophthalmic Exam
    • Lethargy Lethargy A general state of sluggishness, listless, or uninterested, with being tired, and having difficulty concentrating and doing simple tasks. It may be related to depression or drug addiction. Hyponatremia

Contraindications Contraindications A condition or factor associated with a recipient that makes the use of a drug, procedure, or physical agent improper or inadvisable. Contraindications may be absolute (life threatening) or relative (higher risk of complications in which benefits may outweigh risks). Noninvasive Ventilation

  • Use should be avoided:
    • AV block AV block Atrioventricular (AV) block is a bradyarrhythmia caused by delay, or interruption, in the electrical conduction between the atria and the ventricles. Atrioventricular block occurs due to either anatomic or functional impairment, and is classified into 3 types. Atrioventricular block (AV block)
    • Wolff-Parkinson-White (WPW) syndrome
    • Ventricular fibrillation Ventricular fibrillation Ventricular fibrillation (VF or V-fib) is a type of ventricular tachyarrhythmia (> 300/min) often preceded by ventricular tachycardia. In this arrhythmia, the ventricle beats rapidly and sporadically. The ventricular contraction is uncoordinated, leading to a decrease in cardiac output and immediate hemodynamic collapse. Ventricular Fibrillation (V-fib) ( V-fib V-fib Ventricular fibrillation (VF or V-fib) is a type of ventricular tachyarrhythmia (> 300/min) often preceded by ventricular tachycardia. In this arrhythmia, the ventricle beats rapidly and sporadically. The ventricular contraction is uncoordinated, leading to a decrease in cardiac output and immediate hemodynamic collapse. Ventricular Fibrillation (V-fib))
    • Electrolyte abnormalities:
      • Hypokalemia Hypokalemia Hypokalemia is defined as plasma potassium (K+) concentration < 3.5 mEq/L. Homeostatic mechanisms maintain plasma concentration between 3.5-5.2 mEq/L despite marked variation in dietary intake. Hypokalemia can be due to renal losses, GI losses, transcellular shifts, or poor dietary intake. Hypokalemia
      • Hypomagnesemia Hypomagnesemia A nutritional condition produced by a deficiency of magnesium in the diet, characterized by anorexia, nausea, vomiting, lethargy, and weakness. Symptoms are paresthesias, muscle cramps, irritability, decreased attention span, and mental confusion, possibly requiring months to appear. Deficiency of body magnesium can exist even when serum values are normal. In addition, magnesium deficiency may be organ-selective, since certain tissues become deficient before others. Electrolytes
      • Hypercalcemia Hypercalcemia Hypercalcemia (serum calcium > 10.5 mg/dL) can result from various conditions, the majority of which are due to hyperparathyroidism and malignancy. Other causes include disorders leading to vitamin D elevation, granulomatous diseases, and the use of certain pharmacological agents. Symptoms vary depending on calcium levels and the onset of hypercalcemia. Hypercalcemia 
  • Use with caution:
    • Renal failure Renal failure Conditions in which the kidneys perform below the normal level in the ability to remove wastes, concentrate urine, and maintain electrolyte balance; blood pressure; and calcium metabolism. Renal insufficiency can be classified by the degree of kidney damage (as measured by the level of proteinuria) and reduction in glomerular filtration rate. Crush Syndrome
    • Elderly patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship 
    • Thyroid Thyroid The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland: Anatomy disease 
    • Acute coronary syndrome (ACS): may ↑ myocardial oxygen demand Myocardial oxygen demand Stable and Unstable Angina ischemia Ischemia A hypoperfusion of the blood through an organ or tissue caused by a pathologic constriction or obstruction of its blood vessels, or an absence of blood circulation. Ischemic Cell Damage
    • Hypertrophic cardiomyopathy Cardiomyopathy Cardiomyopathy refers to a group of myocardial diseases associated with structural changes of the heart muscles (myocardium) and impaired systolic and/or diastolic function in the absence of other heart disorders (coronary artery disease, hypertension, valvular disease, and congenital heart disease). Cardiomyopathy: Overview and Types ( HCM HCM Hypertrophic cardiomyopathy (HCM) is the most commonly inherited cardiomyopathy, which is characterized by an asymmetric increase in thickness (hypertrophy) of the left ventricular wall, diastolic dysfunction, and often left ventricular outflow tract obstruction. Hypertrophic Cardiomyopathy) with left ventricular outflow tract obstruction Left ventricular outflow tract obstruction Hypertrophic Cardiomyopathy
    • 2nd- or 3rd-degree heart block: unless a functioning pacemaker Pacemaker A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external). Bradyarrhythmias is placed

Drug interactions

  • ↑ AV blocking/bradycardic effect:
  • ↑ Risk of toxicity Toxicity Dosage Calculation due to:
    • Digoxin Digoxin A cardiotonic glycoside obtained mainly from digitalis lanata; it consists of three sugars and the aglycone digoxigenin. Digoxin has positive inotropic and negative chronotropic activity. It is used to control ventricular rate in atrial fibrillation and in the management of congestive heart failure with atrial fibrillation. Its use in congestive heart failure and sinus rhythm is less certain. The margin between toxic and therapeutic doses is small. Cardiac Glycosides concentration:
      • Amiodarone Amiodarone An antianginal and class III antiarrhythmic drug. It increases the duration of ventricular and atrial muscle action by inhibiting potassium channels and voltage-gated sodium channels. There is a resulting decrease in heart rate and in vascular resistance. Pulmonary Fibrosis
      • Quinidine Quinidine An optical isomer of quinine, extracted from the bark of the cinchona tree and similar plant species. This alkaloid dampens the excitability of cardiac and skeletal muscles by blocking sodium and potassium currents across cellular membranes. It prolongs cellular action potentials, and decreases automaticity. Quinidine also blocks muscarinic and alpha-adrenergic neurotransmission. Class 1 Antiarrhythmic Drugs (Sodium Channel Blockers)
      • Spironolactone Spironolactone A potassium sparing diuretic that acts by antagonism of aldosterone in the distal renal tubules. It is used mainly in the treatment of refractory edema in patients with congestive heart failure, nephrotic syndrome, or hepatic cirrhosis. Its effects on the endocrine system are utilized in the treatments of hirsutism and acne but they can lead to adverse effects. Potassium-sparing Diuretics
    • Hypokalemia Hypokalemia Hypokalemia is defined as plasma potassium (K+) concentration < 3.5 mEq/L. Homeostatic mechanisms maintain plasma concentration between 3.5-5.2 mEq/L despite marked variation in dietary intake. Hypokalemia can be due to renal losses, GI losses, transcellular shifts, or poor dietary intake. Hypokalemia and/or hypomagnesemia Hypomagnesemia A nutritional condition produced by a deficiency of magnesium in the diet, characterized by anorexia, nausea, vomiting, lethargy, and weakness. Symptoms are paresthesias, muscle cramps, irritability, decreased attention span, and mental confusion, possibly requiring months to appear. Deficiency of body magnesium can exist even when serum values are normal. In addition, magnesium deficiency may be organ-selective, since certain tissues become deficient before others. Electrolytes:

Adenosine

Chemistry

Adenosine is a naturally occurring purine nucleoside base.

Mechanism of action

Cardiac Cardiac Total Anomalous Pulmonary Venous Return (TAPVR) nodal cells:

Vascular smooth muscle cells:

  • Adenosine type 2 Type 2 Spinal Muscular Atrophy receptors Receptors Receptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell. Receptors → G-protein activation → adenylyl cyclase stimulation 
  • CAMP cAMP An adenine nucleotide containing one phosphate group which is esterified to both the 3′- and 5′-positions of the sugar moiety. It is a second messenger and a key intracellular regulator, functioning as a mediator of activity for a number of hormones, including epinephrine, glucagon, and acth. Phosphodiesterase Inhibitors protein kinase Protein kinase A family of enzymes that catalyze the conversion of ATP and a protein to adp and a phosphoprotein. Interferons activation → stimulates K channels Channels The Cell: Cell Membrane hyperpolarization Hyperpolarization Membrane Potential
  • Vascular smooth muscle relaxation → vasodilation Vasodilation The physiological widening of blood vessels by relaxing the underlying vascular smooth muscle. Pulmonary Hypertension Drugs

Pharmacokinetics Pharmacokinetics Pharmacokinetics is the science that analyzes how the human body interacts with a drug. Pharmacokinetics examines how the drug is absorbed, distributed, metabolized, and excreted by the body. Pharmacokinetics and Pharmacodynamics

  • Absorption Absorption Absorption involves the uptake of nutrient molecules and their transfer from the lumen of the GI tract across the enterocytes and into the interstitial space, where they can be taken up in the venous or lymphatic circulation. Digestion and Absorption:
    • Route of administration: IV
    • Immediate onset
  • Metabolism and excretion: 
    • Half-life Half-Life The time it takes for a substance (drug, radioactive nuclide, or other) to lose half of its pharmacologic, physiologic, or radiologic activity. Pharmacokinetics and Pharmacodynamics: < 10 seconds
    • Rapid cellular uptake by vascular endothelium Endothelium A layer of epithelium that lines the heart, blood vessels (vascular endothelium), lymph vessels (lymphatic endothelium), and the serous cavities of the body. Arteries: Histology and erythrocytes Erythrocytes Erythrocytes, or red blood cells (RBCs), are the most abundant cells in the blood. While erythrocytes in the fetus are initially produced in the yolk sac then the liver, the bone marrow eventually becomes the main site of production. Erythrocytes: Histology
    • Metabolized intracellularly to: 
      • AMP
      • Inosine → uric acid Uric acid An oxidation product, via xanthine oxidase, of oxypurines such as xanthine and hypoxanthine. It is the final oxidation product of purine catabolism in humans and primates, whereas in most other mammals urate oxidase further oxidizes it to allantoin. Nephrolithiasis → excreted by kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys: Anatomy

Indications

  • Arrhythmias:
    • Used in cardioversion Cardioversion Atrial Fibrillation of paroxysmal SVT SVT Supraventricular tachycardias are related disorders in which the elevation in heart rate is driven by pathophysiology in the atria. This group falls under the larger umbrella of tachyarrhythmias and includes paroxysmal supraventricular tachycardias (PSVTs), ventricular pre-excitation syndromes (i.e. Wolff-Parkinson-White syndrome), atrial flutter, multifocal atrial tachycardia, and atrial fibrillation. Supraventricular Tachycardias (PSVT) to normal sinus rhythm Normal sinus rhythm Electrocardiogram (ECG)
    • Transient AV blockade can aid in diagnosis of a tachyarrhythmia Tachyarrhythmia A tachyarrhythmia is a rapid heart rhythm, regular or irregular, with a rate > 100 beats/min. Tachyarrhythmia may or may not be accompanied by symptoms of hemodynamic change. Tachyarrhythmias caused by AFib Afib Atrial fibrillation (AF or Afib) is a supraventricular tachyarrhythmia and the most common kind of arrhythmia. It is caused by rapid, uncontrolled atrial contractions and uncoordinated ventricular responses. Atrial Fibrillation or AFL.
    • Not effective for converting AFib Afib Atrial fibrillation (AF or Afib) is a supraventricular tachyarrhythmia and the most common kind of arrhythmia. It is caused by rapid, uncontrolled atrial contractions and uncoordinated ventricular responses. Atrial Fibrillation or AFL
  • Diagnostic aid in myocardial perfusion scintigraphy Scintigraphy Sjögren’s Syndrome:
    • Causes vasodilation Vasodilation The physiological widening of blood vessels by relaxing the underlying vascular smooth muscle. Pulmonary Hypertension Drugs of the coronary arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology → ↑ blood flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure in the normal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology but not in stenotic coronary arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology 
    • ↓ Thallium-201 uptake in stenotic arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology → allows visualization of areas with insufficient blood flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure
The use of adenosine in tachyarrhythmias 5 antiarrythmics

The use of adenosine in tachyarrhythmias:
A: Adenosine can be used to convert supraventricular tachycardias (SVTs), such as atrioventricular node Atrioventricular node A small nodular mass of specialized muscle fibers located in the interatrial septum near the opening of the coronary sinus. It gives rise to the atrioventricular bundle of the conduction system of the heart. Heart: Anatomy ( AVN Avn Hip Fractures) reentry tachycardia Tachycardia Abnormally rapid heartbeat, usually with a heart rate above 100 beats per minute for adults. Tachycardia accompanied by disturbance in the cardiac depolarization (cardiac arrhythmia) is called tachyarrhythmia. Sepsis in Children. Transient blockade of the AVN Avn Hip Fractures (noted by the long pause) terminates the reentry circuit, allowing for the resumption of normal sinus rhythm Normal sinus rhythm Electrocardiogram (ECG).
B: Sometimes, the underlying rhythm is not certain. Transient AVN Avn Hip Fractures blockade may allow for rhythm identification Identification Defense Mechanisms in these cases. This is demonstrated by the uncovering of “sawtooth” flutter waves due to atrial flutter Atrial flutter Atrial flutter is a regular supraventricular tachycardia characterized by an atrial heart rate between 240/min and 340/min (typically 300/min), atrioventricular (AV) node conduction block, and a “sawtooth” pattern on an electrocardiogram (ECG). Atrial Flutter (AFL).

Image by Lecturio.

Adverse effects

  • Common short-lived symptoms:
    • Flushing
    • Diaphoresis
    • Dizziness Dizziness An imprecise term which may refer to a sense of spatial disorientation, motion of the environment, or lightheadedness. Lateral Medullary Syndrome (Wallenberg Syndrome)
    • Chest pain Chest Pain Chest pain is one of the most common and challenging complaints that may present in an inpatient and outpatient setting. The differential diagnosis of chest pain is large and includes cardiac, gastrointestinal, pulmonary, musculoskeletal, and psychiatric etiologies. Chest Pain 
    • Nausea Nausea An unpleasant sensation in the stomach usually accompanied by the urge to vomit. Common causes are early pregnancy, sea and motion sickness, emotional stress, intense pain, food poisoning, and various enteroviruses. Antiemetics
    • Anxiety Anxiety Feelings or emotions of dread, apprehension, and impending disaster but not disabling as with anxiety disorders. Generalized Anxiety Disorder 
    • Feeling of impending doom 
  • Cardiovascular events:
    • Hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension
    • Transient or new arrhythmias:
      • AFib Afib Atrial fibrillation (AF or Afib) is a supraventricular tachyarrhythmia and the most common kind of arrhythmia. It is caused by rapid, uncontrolled atrial contractions and uncoordinated ventricular responses. Atrial Fibrillation/AFL
      • High-degree heart block
    • Cardiac Cardiac Total Anomalous Pulmonary Venous Return (TAPVR) arrest
    • Myocardial ischemia Ischemia A hypoperfusion of the blood through an organ or tissue caused by a pathologic constriction or obstruction of its blood vessels, or an absence of blood circulation. Ischemic Cell Damage
    • Cerebrovascular accident Cerebrovascular accident An ischemic stroke (also known as cerebrovascular accident) is an acute neurologic injury that occurs as a result of brain ischemia; this condition may be due to cerebral blood vessel occlusion by thrombosis or embolism, or rarely due to systemic hypoperfusion. Ischemic Stroke
  • Pulmonary events:
    • Dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea 
    • Bronchospasm Bronchospasm Asthma Drugs

Contraindications Contraindications A condition or factor associated with a recipient that makes the use of a drug, procedure, or physical agent improper or inadvisable. Contraindications may be absolute (life threatening) or relative (higher risk of complications in which benefits may outweigh risks). Noninvasive Ventilation

  • Hypersensitivity to adenosine
  • Clinically active bronchospasm Bronchospasm Asthma Drugs
  • 2nd- or 3rd-degree AV block AV block Atrioventricular (AV) block is a bradyarrhythmia caused by delay, or interruption, in the electrical conduction between the atria and the ventricles. Atrioventricular block occurs due to either anatomic or functional impairment, and is classified into 3 types. Atrioventricular block (AV block)
  • Sick sinus syndrome Sick Sinus Syndrome Sick sinus syndrome (SSS), also known as sinus node dysfunction, is characterized by degeneration of the sinoatrial (SA) node, the heart’s primary pacemaker. Patients with SSS may be asymptomatic or may present with tachycardia or bradycardia. Sick Sinus Syndrome ( SSS SSS Sick sinus syndrome (SSS), also known as sinus node dysfunction, is characterized by degeneration of the sinoatrial (SA) node, the heart’s primary pacemaker. Patients with SSS may be asymptomatic or may present with tachycardia or bradycardia. Sick Sinus Syndrome)
  • Symptomatic bradycardia Bradycardia Bradyarrhythmia is a rhythm in which the heart rate is less than 60/min. Bradyarrhythmia can be physiologic, without symptoms or hemodynamic change. Pathologic bradyarrhythmia results in reduced cardiac output and hemodynamic instability causing syncope, dizziness, or dyspnea. Bradyarrhythmias
  • WPW with preexcitation AFib Afib Atrial fibrillation (AF or Afib) is a supraventricular tachyarrhythmia and the most common kind of arrhythmia. It is caused by rapid, uncontrolled atrial contractions and uncoordinated ventricular responses. Atrial Fibrillation/AFL → can cause degeneration to V-fib V-fib Ventricular fibrillation (VF or V-fib) is a type of ventricular tachyarrhythmia (> 300/min) often preceded by ventricular tachycardia. In this arrhythmia, the ventricle beats rapidly and sporadically. The ventricular contraction is uncoordinated, leading to a decrease in cardiac output and immediate hemodynamic collapse. Ventricular Fibrillation (V-fib)

Drug interactions

  • ↓ Efficacy of adenosine (adenosine receptor Receptor Receptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell. Receptors antagonists):
    • Caffeine Caffeine A methylxanthine naturally occurring in some beverages and also used as a pharmacological agent. Caffeine’s most notable pharmacological effect is as a central nervous system stimulant, increasing alertness and producing agitation. Several cellular actions of caffeine have been observed, but it is not entirely clear how each contributes to its pharmacological profile. Among the most important are inhibition of cyclic nucleotide phosphodiesterases, antagonism of adenosine receptors, and modulation of intracellular calcium handling. Stimulants
    • Theophylline Theophylline A methyl xanthine derivative from tea with diuretic, smooth muscle relaxant, bronchial dilation, cardiac and central nervous system stimulant activities. Theophylline inhibits the 3. Asthma Drugs
  • ↑ Effect of adenosine ( AVN Avn Hip Fractures blockade and/or adverse effects):
    • Carbamazepine Carbamazepine A dibenzazepine that acts as a sodium channel blocker. It is used as an anticonvulsant for the treatment of grand mal and psychomotor or focal seizures. It may also be used in the management of bipolar disorder, and has analgesic properties. First-Generation Anticonvulsant Drugs
    • Dipyridamole Dipyridamole A phosphodiesterase inhibitor that blocks uptake and metabolism of adenosine by erythrocytes and vascular endothelial cells. Dipyridamole also potentiates the antiaggregating action of prostacyclin. Phosphodiesterase Inhibitors
    • Nicotine Nicotine Nicotine is highly toxic alkaloid. It is the prototypical agonist at nicotinic cholinergic receptors where it dramatically stimulates neurons and ultimately blocks synaptic transmission. Nicotine is also important medically because of its presence in tobacco smoke. Stimulants
    • Digoxin Digoxin A cardiotonic glycoside obtained mainly from digitalis lanata; it consists of three sugars and the aglycone digoxigenin. Digoxin has positive inotropic and negative chronotropic activity. It is used to control ventricular rate in atrial fibrillation and in the management of congestive heart failure with atrial fibrillation. Its use in congestive heart failure and sinus rhythm is less certain. The margin between toxic and therapeutic doses is small. Cardiac Glycosides
    • Verapamil Verapamil A calcium channel blocker that is a class IV anti-arrhythmia agent. Pulmonary Hypertension Drugs

Magnesium (Mg) Sulfate

Mechanism of action

Pharmacokinetics Pharmacokinetics Pharmacokinetics is the science that analyzes how the human body interacts with a drug. Pharmacokinetics examines how the drug is absorbed, distributed, metabolized, and excreted by the body. Pharmacokinetics and Pharmacodynamics

Magnesium Magnesium A metallic element that has the atomic symbol mg, atomic number 12, and atomic weight 24. 31. It is important for the activity of many enzymes, especially those involved in oxidative phosphorylation. Electrolytes supplementation for arrhythmias is usually administered IV as Mg sulfate.

  • Onset of action: immediate
  • Duration of action: 30 minutes
  • Excretion: renal

Indications

Magnesium Magnesium A metallic element that has the atomic symbol mg, atomic number 12, and atomic weight 24. 31. It is important for the activity of many enzymes, especially those involved in oxidative phosphorylation. Electrolytes is used as an antiarrhythmic for:

  • QT prolongation and torsades de pointes Torsades de pointes A malignant form of polymorphic ventricular tachycardia that is characterized by heart rate between 200 and 250 beats per minute, and QRS complexes with changing amplitude and twisting of the points. The term also describes the syndrome of tachycardia with prolonged ventricular repolarization, long qt intervals exceeding 500 milliseconds or bradycardia. Torsades de pointes may be self-limited or may progress to ventricular fibrillation. Ventricular Tachycardia
  • Digoxin toxicity Digoxin Toxicity Cardiac Glycosides
  • Other hypomagnesemia-induced arrhythmias 
    • SVT SVT Supraventricular tachycardias are related disorders in which the elevation in heart rate is driven by pathophysiology in the atria. This group falls under the larger umbrella of tachyarrhythmias and includes paroxysmal supraventricular tachycardias (PSVTs), ventricular pre-excitation syndromes (i.e. Wolff-Parkinson-White syndrome), atrial flutter, multifocal atrial tachycardia, and atrial fibrillation. Supraventricular Tachycardias 
    • AFib Afib Atrial fibrillation (AF or Afib) is a supraventricular tachyarrhythmia and the most common kind of arrhythmia. It is caused by rapid, uncontrolled atrial contractions and uncoordinated ventricular responses. Atrial Fibrillation/AFL
    • Ventricular tachycardia Tachycardia Abnormally rapid heartbeat, usually with a heart rate above 100 beats per minute for adults. Tachycardia accompanied by disturbance in the cardiac depolarization (cardiac arrhythmia) is called tachyarrhythmia. Sepsis in Children/ V-fib V-fib Ventricular fibrillation (VF or V-fib) is a type of ventricular tachyarrhythmia (> 300/min) often preceded by ventricular tachycardia. In this arrhythmia, the ventricle beats rapidly and sporadically. The ventricular contraction is uncoordinated, leading to a decrease in cardiac output and immediate hemodynamic collapse. Ventricular Fibrillation (V-fib)

Adverse effects

  • Facial flushing
  • Hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension
  • Diminished reflexes
  • Respiratory depression
  • Asystole Asystole No discernible electrical activity, flatline on electrocardiogram (P waves and QRS complexes are not present). Cardiac Arrest

Warnings and precautions

Magnesium Magnesium A metallic element that has the atomic symbol mg, atomic number 12, and atomic weight 24. 31. It is important for the activity of many enzymes, especially those involved in oxidative phosphorylation. Electrolytes should be used with caution in patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with:

  • Neuromuscular disorders, especially myasthenia gravis Myasthenia Gravis Myasthenia gravis (MG) is an autoimmune neuromuscular disorder characterized by weakness and fatigability of skeletal muscles caused by dysfunction/destruction of acetylcholine receptors at the neuromuscular junction. MG presents with fatigue, ptosis, diplopia, dysphagia, respiratory difficulties, and progressive weakness in the limbs, leading to difficulty in movement. Myasthenia Gravis (MG) → worsened symptoms
  • Renal impairment → hypermagnesemia Hypermagnesemia Electrolytes

Drug interactions

  • Gabapentin Gabapentin A cyclohexane-gamma-aminobutyric acid derivative that is used for the treatment of partial seizures; neuralgia; and restless legs syndrome. Second-Generation Anticonvulsant Drugs: ↑ depressive effect 
  • Neuromuscular blocking agents: ↑ neuromuscular blocking effect
  • Dihydropyridine Dihydropyridine Pyridine moieties which are partially saturated by the addition of two hydrogen atoms in any position. Class 4 Antiarrhythmic Drugs (Calcium Channel Blockers) CCBs CCBs Calcium channel blockers (CCBS) are a class of medications that inhibit voltage-dependent L-type calcium channels of cardiac and vascular smooth muscle cells. The inhibition of these channels produces vasodilation and myocardial depression. There are 2 major classes of CCBS: dihydropyridines and non-dihydropyridines. Class 4 Antiarrhythmic Drugs (Calcium Channel Blockers): ↑ risk of hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension or muscle weakness

Atropine

Mechanism of action

  • Competitive antagonist of acetylcholine Acetylcholine A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. Receptors and Neurotransmitters of the CNS at muscarinic receptors Receptors Receptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell. Receptors → blocks vagal effect on the heart 
  • This leads to:

Pharmacokinetics Pharmacokinetics Pharmacokinetics is the science that analyzes how the human body interacts with a drug. Pharmacokinetics examines how the drug is absorbed, distributed, metabolized, and excreted by the body. Pharmacokinetics and Pharmacodynamics

  • Absorption Absorption Absorption involves the uptake of nutrient molecules and their transfer from the lumen of the GI tract across the enterocytes and into the interstitial space, where they can be taken up in the venous or lymphatic circulation. Digestion and Absorption:
    • Rapid
    • Well absorbed
    • Onset of action:
      • IV: almost immediate
      • IM: 15–30 minutes
  • Distribution:
    • Widely throughout the body
    • Crosses the blood-brain barrier Blood-brain barrier Specialized non-fenestrated tightly-joined endothelial cells with tight junctions that form a transport barrier for certain substances between the cerebral capillaries and the brain tissue. Systemic and Special Circulations
    • Protein binding: 14%–44%
  • Metabolism: hepatic via enzymatic hydrolysis Hydrolysis The process of cleaving a chemical compound by the addition of a molecule of water. Proteins and Peptides
  • Excretion: urine Urine Liquid by-product of excretion produced in the kidneys, temporarily stored in the bladder until discharge through the urethra. Bowen Disease and Erythroplasia of Queyrat

Indications

  • Arrhythmia: 
    • Symptomatic or unstable bradyarrhythmias Bradyarrhythmias Bradyarrhythmia is a rhythm in which the heart rate is less than 60/min. Bradyarrhythmia can be physiologic, without symptoms or hemodynamic change. Pathologic bradyarrhythmia results in reduced cardiac output and hemodynamic instability causing syncope, dizziness, or dyspnea. Bradyarrhythmias
    • Not usually effective for:
      • 2nd-degree AV block AV block Atrioventricular (AV) block is a bradyarrhythmia caused by delay, or interruption, in the electrical conduction between the atria and the ventricles. Atrioventricular block occurs due to either anatomic or functional impairment, and is classified into 3 types. Atrioventricular block (AV block), Mobitz type 2 Type 2 Spinal Muscular Atrophy
      • 3rd-degree AV block AV block Atrioventricular (AV) block is a bradyarrhythmia caused by delay, or interruption, in the electrical conduction between the atria and the ventricles. Atrioventricular block occurs due to either anatomic or functional impairment, and is classified into 3 types. Atrioventricular block (AV block)
  • Other indications:
    • Muscarine-containing mushroom poisoning
    • Organophosphate poisoning
    • ↓ Salivation and respiratory secretions

Adverse effects

  • Anticholinergic Anticholinergic Anticholinergic drugs block the effect of the neurotransmitter acetylcholine at the muscarinic receptors in the central and peripheral nervous systems. Anticholinergic agents inhibit the parasympathetic nervous system, resulting in effects on the smooth muscle in the respiratory tract, vascular system, urinary tract, GI tract, and pupils of the eyes. Anticholinergic Drugs effects:
    • Tachycardia Tachycardia Abnormally rapid heartbeat, usually with a heart rate above 100 beats per minute for adults. Tachycardia accompanied by disturbance in the cardiac depolarization (cardiac arrhythmia) is called tachyarrhythmia. Sepsis in Children
    • Pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil’s size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Pupil: Physiology and Abnormalities dilation and blurred vision Vision Ophthalmic Exam
    • Dry mouth
    • Constipation Constipation Constipation is common and may be due to a variety of causes. Constipation is generally defined as bowel movement frequency < 3 times per week. Patients who are constipated often strain to pass hard stools. The condition is classified as primary (also known as idiopathic or functional constipation) or secondary, and as acute or chronic. Constipation
    • Urinary retention Urinary retention Inability to empty the urinary bladder with voiding (urination). Delirium
    • Anhidrosis
    • Hallucinations Hallucinations Subjectively experienced sensations in the absence of an appropriate stimulus, but which are regarded by the individual as real. They may be of organic origin or associated with mental disorders. Schizophrenia and behavioral changes
  • Hypersensitivity, including anaphylactic reactions Anaphylactic reactions An acute hypersensitivity reaction due to exposure to a previously encountered antigen. The reaction may include rapidly progressing urticaria, respiratory distress, vascular collapse, systemic shock, and death. Vaccination

Contraindications Contraindications A condition or factor associated with a recipient that makes the use of a drug, procedure, or physical agent improper or inadvisable. Contraindications may be absolute (life threatening) or relative (higher risk of complications in which benefits may outweigh risks). Noninvasive Ventilation

  • Narrow-angle glaucoma Glaucoma Glaucoma is an optic neuropathy characterized by typical visual field defects and optic nerve atrophy seen as optic disc cupping on examination. The acute form of glaucoma is a medical emergency. Glaucoma is often, but not always, caused by increased intraocular pressure (IOP). Glaucoma: may precipitate acute glaucoma Acute glaucoma An ocular disease, occurring in many forms, having as its primary characteristics an unstable or a sustained increase in the intraocular pressure which the eye cannot withstand without damage to its structure or impairment of its function. The consequences of the increased pressure may be manifested in a variety of symptoms, depending upon type and severity, such as excavation of the optic disk, hardness of the eyeball, corneal anesthesia, reduced visual acuity, seeing of colored halos around lights, disturbed dark adaptation, visual field defects, and headaches. Osmotic Diuretics
  • MG: may precipitate a myasthenic crisis

Drug interactions

  • The following medications may enhance the anticholinergic Anticholinergic Anticholinergic drugs block the effect of the neurotransmitter acetylcholine at the muscarinic receptors in the central and peripheral nervous systems. Anticholinergic agents inhibit the parasympathetic nervous system, resulting in effects on the smooth muscle in the respiratory tract, vascular system, urinary tract, GI tract, and pupils of the eyes. Anticholinergic Drugs effects of atropine Atropine An alkaloid, originally from atropa belladonna, but found in other plants, mainly solanaceae. Hyoscyamine is the 3(s)-endo isomer of atropine. Anticholinergic Drugs:
    • Amantadine Amantadine An antiviral that is used in the prophylactic or symptomatic treatment of influenza A. It is also used as an antiparkinsonian agent, to treat extrapyramidal reactions, and for postherpetic neuralgia. The mechanisms of its effects in movement disorders are not well understood but probably reflect an increase in synthesis and release of dopamine, with perhaps some inhibition of dopamine uptake. Antivirals for Influenza
    • Botulinum toxin Botulinum toxin Toxic proteins produced from the species Clostridium botulinum. The toxins are synthesized as a single peptide chain which is processed into a mature protein consisting of a heavy chain and light chain joined via a disulfide bond. The botulinum toxin light chain is a zinc-dependent protease which is released from the heavy chain upon endocytosis into presynaptic nerve endings. Once inside the cell the botulinum toxin light chain cleaves specific snare proteins which are essential for secretion of acetylcholine by synaptic vesicles. This inhibition of acetylcholine release results in muscular paralysis. Botulism
    • Glycopyrrolate Glycopyrrolate A muscarinic antagonist used as an antispasmodic, in some disorders of the gastrointestinal tract, and to reduce salivation with some anesthetics. Anticholinergic Drugs
    • Mirabegron
  • Atropine Atropine An alkaloid, originally from atropa belladonna, but found in other plants, mainly solanaceae. Hyoscyamine is the 3(s)-endo isomer of atropine. Anticholinergic Drugs may: 
    • ↓ The absorption Absorption Absorption involves the uptake of nutrient molecules and their transfer from the lumen of the GI tract across the enterocytes and into the interstitial space, where they can be taken up in the venous or lymphatic circulation. Digestion and Absorption of nitroglycerin Nitroglycerin A volatile vasodilator which relieves angina pectoris by stimulating guanylate cyclase and lowering cytosolic calcium. It is also sometimes used for tocolysis and explosives. Nitrates
    • ↓ Therapeutic effect of acetylcholinesterase (AChE) inhibitors
    • ↑ Constipating and/or urinary retention Urinary retention Inability to empty the urinary bladder with voiding (urination). Delirium side effects of:
      • Clozapine Clozapine A tricyclic dibenzodiazepine, classified as an atypical antipsychotic agent. It binds several types of central nervous system receptors, and displays a unique pharmacological profile. Clozapine is a serotonin antagonist, with strong binding to 5-HT 2a/2c receptor subtype. It also displays strong affinity to several dopaminergic receptors, but shows only weak antagonism at the dopamine D2 receptor, a receptor commonly thought to modulate neuroleptic activity. Agranulocytosis is a major adverse effect associated with administration of this agent. Second-Generation Antipsychotics
      • Opioid agonists Opioid Agonists Antidiarrheal Drugs

References

  1. Levine, E. (2019). Classification of arrhythmic agents. Medscape. Retrieved August 12, 2021, from https://emedicine.medscape.com/article/2172024-overview
  2. Makielski, JC, & Eckhardt, LL. (2019). Cardiac excitability, mechanisms of arrhythmias, and action of antiarrhythmic drugs. UpToDate. Retrieved July 22, 2021, from https://www.uptodate.com/contents/cardiac-excitability-mechanisms-of-arrhythmia-and-action-of-antiarrhythmic-drugs
  3. Digoxin: Drug information. UpToDate. Retrieved July 22, 2021, from https://www.uptodate.com/contents/digoxin-drug-information
  4. Magnesium sulfate: Drug information. UpToDate. Retrieved July 22, 2021, from https://www.uptodate.com/contents/magnesium-sulfate-drug-information
  5. Adenosine: Drug information.  UpToDate. Retrieved July 22, 2021, from https://www.uptodate.com/contents/adenosine-drug-information
  6. Atropine: Drug information.  UpToDate. Retrieved July 22, 2021, from https://www.uptodate.com/contents/atropine-systemic-drug-information
  7. Hume, JR, & Grant, AO. (2012). Agents used in cardiac arrhythmias. In Katzung, BG, Masters, SB, & Trevor, AJ. (Eds.), Basic & clinical pharmacology (12th edition, pp. 227–250). https://pharmacomedicale.org/images/cnpm/CNPM_2016/katzung-pharmacology.pdf
  8. David, MNV, & Shetty, M. (2021). Digoxin. StatPearls. Retrieved August 26, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK556025/
  9. Singh, S, & McKintosh, R. (2021). Adenosine. StatPearls. Retrieved August 26, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK519049/
  10. Hicks, MA, & Tyagi, A. (2021). Magnesium sulfate. StatPearls. Retrieved August 26, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK554553/
  11. Voster, A. (2017). The pharmacology of amiodarone and digoxin as antiarrhythmic agents. Part I Anesthesia Refresher Course. University of Cape Town. http://www.anaesthesia.uct.ac.za/sites/default/files/image_tool/images/93/2017-29-Digoxin%20and%20Amiodarone%20%28A%20Vorster%29.pdf

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