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Thyroid Replacement Therapy

The 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 gland produces hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types called thyroxine Thyroxine The major hormone derived from the thyroid gland. Thyroxine is synthesized via the iodination of tyrosines (monoiodotyrosine) and the coupling of iodotyrosines (diiodotyrosine) in the thyroglobulin. Thyroxine is released from thyroglobulin by proteolysis and secreted into the blood. Thyroid Hormones (T4) and triiodothyronine Triiodothyronine A T3 thyroid hormone normally synthesized and secreted by the thyroid gland in much smaller quantities than thyroxine (T4). Most T3 is derived from peripheral monodeiodination of T4 at the 5' position of the outer ring of the iodothyronine nucleus. The hormone finally delivered and used by the tissues is mainly t3. Thyroid Hormones (T3), which play important roles in processes such as metabolism, tissue growth, development, and in other regulatory pathways. When an individual’s 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 does not produce enough hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types to maintain these processes, they are given synthetic or nonsynthetic forms of T3 and T4. These medications include levothyroxine, liothyronine, and desiccated 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 extract. Correct dosing and intake of these hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types is important. Overdosing can cause symptoms of hyperthyroidism Hyperthyroidism Hypersecretion of thyroid hormones from the thyroid gland. Elevated levels of thyroid hormones increase basal metabolic rate. Thyrotoxicosis and Hyperthyroidism, and underdosing may not fully resolve the symptoms of hypothyroidism Hypothyroidism Hypothyroidism is a condition characterized by a deficiency of thyroid hormones. Iodine deficiency is the most common cause worldwide, but Hashimoto's disease (autoimmune thyroiditis) is the leading cause in non-iodine-deficient regions. Hypothyroidism. It is important to be aware of various drug and food interactions that can either decrease or increase the effect of these medications.

Last updated: Sep 1, 2022

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Overview

Pathophysiology of hypothyroidism Hypothyroidism Hypothyroidism is a condition characterized by a deficiency of thyroid hormones. Iodine deficiency is the most common cause worldwide, but Hashimoto’s disease (autoimmune thyroiditis) is the leading cause in non-iodine-deficient regions. Hypothyroidism

  • Medical condition defined by deficiency of 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 hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types
    • Thyroxine Thyroxine The major hormone derived from the thyroid gland. Thyroxine is synthesized via the iodination of tyrosines (monoiodotyrosine) and the coupling of iodotyrosines (diiodotyrosine) in the thyroglobulin. Thyroxine is released from thyroglobulin by proteolysis and secreted into the blood. Thyroid Hormones (T4)
    • Triiodothyronine Triiodothyronine A T3 thyroid hormone normally synthesized and secreted by the thyroid gland in much smaller quantities than thyroxine (T4). Most T3 is derived from peripheral monodeiodination of T4 at the 5′ position of the outer ring of the iodothyronine nucleus. The hormone finally delivered and used by the tissues is mainly t3. Thyroid Hormones (T3
  • These hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types play an integral role in various functions:
  • Clinically, a deficiency in these hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types can lead to abnormal changes in:
    • Energy levels
    • Weight
    • Thermoregulation Thermoregulation Body temperature can be divided into external temperature, which involves the skin, and core temperature, which involves the CNS and viscera. While external temperature can be variable, the core temperature is maintained within a narrow range of 36.5-37.5ºC (97.7-99.5ºF). Body Temperature Regulation
    • HR
    • Bowel movements
    • Mood

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 replacement medications

The 3 drugs used for treatment of hypothyroidism Hypothyroidism Hypothyroidism is a condition characterized by a deficiency of thyroid hormones. Iodine deficiency is the most common cause worldwide, but Hashimoto’s disease (autoimmune thyroiditis) is the leading cause in non-iodine-deficient regions. Hypothyroidism are:

  • Levothyroxine (L-T4)
  • Liothyronine (L-T3)
  • Desiccated 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 extract

Levothyroxine

Pharmacodynamics Pharmacodynamics Pharmacodynamics is the science that studies the biochemical and physiologic effects of a drug and its organ-specific mechanism of action, including effects on the cellular level. Pharmacokinetics is “what the body does to the drug,” whereas pharmacodynamics is “what the drug does to the body.” Pharmacokinetics and Pharmacodynamics

  • Levothyroxine is a synthetic levo-isomer of T4
  • The prohormone T4 is converted to T3 (active) or reverse T3 (inactive) in the 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 and other peripheral tissues via deiodination. 
  • ↑ T4 and T3 levels lead to:
    • Normalization of hormone effects on metabolic, growth, and development functions 
    • Pituitary Pituitary A small, unpaired gland situated in the sella turcica. It is connected to the hypothalamus by a short stalk which is called the infundibulum. Hormones: Overview and Types overproduction of thyroid-stimulating hormone Thyroid-stimulating hormone A glycoprotein hormone secreted by the adenohypophysis. Thyrotropin stimulates thyroid gland by increasing the iodide transport, synthesis and release of thyroid hormones (thyroxine and triiodothyronine). Thyroid Hormones (TSH)

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
    • 40%‒80% absorbed from GI tract; can be erratic 
    • Food can ↓ 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: Approximately 99% of T4 and T3 binds to plasma Plasma The residual portion of blood that is left after removal of blood cells by centrifugation without prior blood coagulation. Transfusion Products 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 (thyroxine-binding globulin ( TBG TBG A thyroid hormone transport protein found in serum. It binds about 75% of circulating thyroxine and 70% of circulating triiodothyronine. Thyroid Hormones)). 
  • Metabolism:
    • Deiodination in the 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 and other peripheral tissues (including 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) to the active form, T3
    • Renal and hepatic impairment can ↓ conversion to T3.
  • Excretion:
    • Urine (primarily)
    • Feces

Indications

  • Hypothyroidism Hypothyroidism Hypothyroidism is a condition characterized by a deficiency of thyroid hormones. Iodine deficiency is the most common cause worldwide, but Hashimoto’s disease (autoimmune thyroiditis) is the leading cause in non-iodine-deficient regions. Hypothyroidism (primary, secondary, and tertiary)
    • Levothyroxine is the drug of choice.
    • Goal is to mimic normal endogenous T4 production
    • Has a longer 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 than L-T3
    • Less chance of hypermetabolic side effects
  • Myxedema Myxedema A condition characterized by a dry, waxy type of swelling (edema) with abnormal deposits of mucopolysaccharides in the skin and other tissues. It is caused by a deficiency of thyroid hormones. The skin becomes puffy around the eyes and on the cheeks. The face is dull and expressionless with thickened nose and lips. Edema coma Coma Coma is defined as a deep state of unarousable unresponsiveness, characterized by a score of 3 points on the GCS. A comatose state can be caused by a multitude of conditions, making the precise epidemiology and prognosis of coma difficult to determine. Coma (in combination with L-T3)
  • TSH suppression Suppression Defense Mechanisms in thyrotropin-dependent 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 cancers (papillary and follicular)

Adverse effects

  • Hypermetabolic state Hypermetabolic State Neurological Examination:
    • Can occur with:
      • Overtreatment 
      • Elderly individuals
      • Initiation of therapy
    • Signs and symptoms:
      • Palpitations Palpitations Ebstein’s Anomaly
      • 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 (including 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)
      • Widened pulse pressure
      • Sweating
      • Weight loss Weight loss Decrease in existing body weight. Bariatric Surgery
      • Diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea 
      • Agitation Agitation A feeling of restlessness associated with increased motor activity. This may occur as a manifestation of nervous system drug toxicity or other conditions. St. Louis Encephalitis Virus and restlessness
  • Allergy Allergy An abnormal adaptive immune response that may or may not involve antigen-specific IgE Type I Hypersensitivity Reaction to the dye or filler:
    • Swelling Swelling Inflammation
    • 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
  • Untreated adrenal insufficiency Adrenal Insufficiency Conditions in which the production of adrenal corticosteroids falls below the requirement of the body. Adrenal insufficiency can be caused by defects in the adrenal glands, the pituitary gland, or the hypothalamus. Adrenal Insufficiency and Addison’s Disease: Levothyroxine can precipitate acute adrenal crisis Adrenal crisis Adrenal crisis is the acute decompensation of adrenal function that can be triggered by another disease, surgery, stress, or increased glucocorticoid inactivation. Adrenal Insufficiency and Addison’s Disease.

Precautions

  • Pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care
    • Associated with ↑ metabolic needs
    • Normal physiologic ↑ in TBG TBG A thyroid hormone transport protein found in serum. It binds about 75% of circulating thyroxine and 70% of circulating triiodothyronine. Thyroid Hormones and TSH → ↑ 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 hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types
    • Pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care: Mothers require ↑ in L-T4 dosage Dosage Dosage Calculation.
    • Remember to change back to prepregnancy dose postpartum.
  • Elderly individuals or those with cardiovascular disease:
    • 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 hormone therapy has inotropic and chronotropic effects on the heart, which can result in angina.
    • Older individuals (> 60 years) and those with cardiovascular disease should be started on a lower dose.
    • This low dose can be slowly titrated upward (“start low, go slow”).
  • Individuals with diabetes mellitus Diabetes mellitus Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia and dysfunction of the regulation of glucose metabolism by insulin. Type 1 DM is diagnosed mostly in children and young adults as the result of autoimmune destruction of β cells in the pancreas and the resulting lack of insulin. Type 2 DM has a significant association with obesity and is characterized by insulin resistance. Diabetes Mellitus may need to have the dosage Dosage Dosage Calculation of their antidiabetes medication adjusted with administration of L-T4.

Drug and food interactions

  • Foods that interfere with 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 (medication should be taken on empty stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy):
    • High-fiber foods
    • Calcium-containing foods
    • Grapefruit
    • Coffee Coffee A beverage made from ground coffee beans (seeds) infused in hot water. It generally contains caffeine and theophylline unless it is decaffeinated. Constipation
  • Drugs that interfere with 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:
    • Calcium Calcium A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes. Electrolytes carbonate
    • Iron Iron A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen. Trace Elements supplements
    • Bile Bile An emulsifying agent produced in the liver and secreted into the duodenum. Its composition includes bile acids and salts; cholesterol; and electrolytes. It aids digestion of fats in the duodenum. Gallbladder and Biliary Tract: Anatomy acid sequestrants 
    • Aluminum-containing antacids
  • Severe drug interactions:
    • Ketamine Ketamine A cyclohexanone derivative used for induction of anesthesia. Its mechanism of action is not well understood, but ketamine can block NMDA receptors (n-methyl-d-aspartate receptors) and may interact with sigma receptors. Intravenous Anesthetics: hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension and 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
    • Tricyclic antidepressants Tricyclic antidepressants Tricyclic antidepressants (TCAs) are a class of medications used in the management of mood disorders, primarily depression. These agents, named after their 3-ring chemical structure, act via reuptake inhibition of neurotransmitters (particularly norepinephrine and serotonin) in the brain. Tricyclic Antidepressants ( TCAs TCAs Tricyclic antidepressants (TCAs) are a class of medications used in the management of mood disorders, primarily depression. These agents, named after their 3-ring chemical structure, act via reuptake inhibition of neurotransmitters (particularly norepinephrine and serotonin) in the brain. Tricyclic Antidepressants): ↑ arrhythmogenic effect

Drugs that may alter levothyroxine efficacy

Table: Drugs that may alter levothyroxine efficacy
Mechanism Drugs Levothyroxine adjustment
Drugs that ↑ hepatic conversion of T4 to T3
  • Phenobarbital Phenobarbital A barbituric acid derivative that acts as a nonselective central nervous system depressant. It potentiates gamma-aminobutyric acid action on gaba-a receptors, and modulates chloride currents through receptor channels. It also inhibits glutamate induced depolarizations. First-Generation Anticonvulsant Drugs
  • Phenytoin Phenytoin An anticonvulsant that is used to treat a wide variety of seizures. The mechanism of therapeutic action is not clear, although several cellular actions have been described including effects on ion channels, active transport, and general membrane stabilization. Phenytoin has been proposed for several other therapeutic uses, but its use has been limited by its many adverse effects and interactions with other drugs. First-Generation Anticonvulsant Drugs
  • 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
  • Rifampin Rifampin A semisynthetic antibiotic produced from streptomyces mediterranei. It has a broad antibacterial spectrum, including activity against several forms of Mycobacterium. In susceptible organisms it inhibits dna-dependent RNA polymerase activity by forming a stable complex with the enzyme. It thus suppresses the initiation of RNA synthesis. Rifampin is bactericidal, and acts on both intracellular and extracellular organisms. Epiglottitis
  • Sertraline Sertraline A selective serotonin uptake inhibitor that is used in the treatment of depression. Serotonin Reuptake Inhibitors and Similar Antidepressants
  • Imatinib Imatinib A tyrosine kinase inhibitor and antineoplastic agent that inhibits the bcr-abl kinase created by chromosome rearrangements in chronic myeloid leukemia and acute lymphoblastic leukemia, as well as pdg-derived tyrosine kinases that are overexpressed in gastrointestinal stromal tumors. Targeted and Other Nontraditional Antineoplastic Therapy
Dosage Dosage Dosage Calculation may be necessary
Drugs that ↑ serum TBG TBG A thyroid hormone transport protein found in serum. It binds about 75% of circulating thyroxine and 70% of circulating triiodothyronine. Thyroid Hormones concentration
  • Estrogen Estrogen Compounds that interact with estrogen receptors in target tissues to bring about the effects similar to those of estradiol. Estrogens stimulate the female reproductive organs, and the development of secondary female sex characteristics. Estrogenic chemicals include natural, synthetic, steroidal, or non-steroidal compounds. Ovaries: Anatomy
  • Tamoxifen Tamoxifen One of the selective estrogen receptor modulators with tissue-specific activities. Tamoxifen acts as an anti-estrogen (inhibiting agent) in the mammary tissue, but as an estrogen (stimulating agent) in cholesterol metabolism, bone density, and cell proliferation in the endometrium. Antiestrogens
  • Raloxifene Raloxifene A second generation selective estrogen receptor modulator (SERM) used to prevent osteoporosis in postmenopausal women. It has estrogen agonist effects on bone and cholesterol metabolism but behaves as a complete estrogen antagonist on mammary gland and uterine tissue. Other Antiresorptive Drugs
  • Clofibrate
  • Opioids Opioids Opiates are drugs that are derived from the sap of the opium poppy. Opiates have been used since antiquity for the relief of acute severe pain. Opioids are synthetic opiates with properties that are substantially similar to those of opiates. Opioid Analgesics
  • Fluorouracil Fluorouracil A pyrimidine analog that is an antineoplastic antimetabolite. It interferes with DNA synthesis by blocking the thymidylate synthetase conversion of deoxyuridylic acid to thymidylic acid. Bowen Disease and Erythroplasia of Queyrat
  • Capecitabine Capecitabine A deoxycytidine derivative and fluorouracil prodrug that is used as an antineoplastic antimetabolite in the treatment of colon cancer; breast cancer and gastric cancer. Antimetabolite Chemotherapy
Dosage Dosage Dosage Calculation may be necessary
Drugs that ↓ serum TBG TBG A thyroid hormone transport protein found in serum. It binds about 75% of circulating thyroxine and 70% of circulating triiodothyronine. Thyroid Hormones concentration
  • Glucocorticoids Glucocorticoids Glucocorticoids are a class within the corticosteroid family. Glucocorticoids are chemically and functionally similar to endogenous cortisol. There are a wide array of indications, which primarily benefit from the antiinflammatory and immunosuppressive effects of this class of drugs. Glucocorticoids
  • Androgens Androgens Androgens are naturally occurring steroid hormones responsible for development and maintenance of the male sex characteristics, including penile, scrotal, and clitoral growth, development of sexual hair, deepening of the voice, and musculoskeletal growth. Androgens and Antiandrogens
Dosage Dosage Dosage Calculation may be necessary

Liothyronine

Pharmacodynamics Pharmacodynamics Pharmacodynamics is the science that studies the biochemical and physiologic effects of a drug and its organ-specific mechanism of action, including effects on the cellular level. Pharmacokinetics is “what the body does to the drug,” whereas pharmacodynamics is “what the drug does to the body.” Pharmacokinetics and Pharmacodynamics

  • Liothyronine is the synthetic form of active T3
  • Effects are stronger and faster than those of L-T4.

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 (approximately 95%)
  • Distribution: approximately 99% bound to 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, such as TBG TBG A thyroid hormone transport protein found in serum. It binds about 75% of circulating thyroxine and 70% of circulating triiodothyronine. Thyroid Hormones
  • Excretion:
    • Urine (primarily)
    • Feces

Indications

  • Hypothyroidism Hypothyroidism Hypothyroidism is a condition characterized by a deficiency of thyroid hormones. Iodine deficiency is the most common cause worldwide, but Hashimoto’s disease (autoimmune thyroiditis) is the leading cause in non-iodine-deficient regions. Hypothyroidism
    • Not typically used alone owing to short 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
    • Used in individuals who continue to have symptoms despite L-T4 therapy
  • Myxedema Myxedema A condition characterized by a dry, waxy type of swelling (edema) with abnormal deposits of mucopolysaccharides in the skin and other tissues. It is caused by a deficiency of thyroid hormones. The skin becomes puffy around the eyes and on the cheeks. The face is dull and expressionless with thickened nose and lips. Edema coma Coma Coma is defined as a deep state of unarousable unresponsiveness, characterized by a score of 3 points on the GCS. A comatose state can be caused by a multitude of conditions, making the precise epidemiology and prognosis of coma difficult to determine. Coma (in conjunction with L-T4)
  • Nontoxic goiter Nontoxic Goiter Goiter

Adverse effects, precautions, and drug interactions

Adverse effects, precautions, and drug interactions are similar to those for L-T4.

Desiccated Thyroid

Pharmacodynamics Pharmacodynamics Pharmacodynamics is the science that studies the biochemical and physiologic effects of a drug and its organ-specific mechanism of action, including effects on the cellular level. Pharmacokinetics is “what the body does to the drug,” whereas pharmacodynamics is “what the drug does to the body.” Pharmacokinetics and Pharmacodynamics

  • Nonsynthetic 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 hormone extracted from the 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 of domesticated animals Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, animalia was one of the kingdoms. Under the modern three domain model, animalia represents one of the many groups in the domain eukaryota. Cell Types: Eukaryotic versus Prokaryotic (e.g., pigs, sheep, cows) 
  • Contains both T3 and T4 in a ratio that does not naturally occur in human beings

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: 40%–80% 
  • Distribution: protein-bound (similar to L-T3 and L-T4)
  • Metabolism: T4 component is converted to T3
  • Excretion:
    • Urine (primarily)
    • Feces

Indications

Desiccated 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 is a rarely used treatment for hypothyroidism Hypothyroidism Hypothyroidism is a condition characterized by a deficiency of thyroid hormones. Iodine deficiency is the most common cause worldwide, but Hashimoto’s disease (autoimmune thyroiditis) is the leading cause in non-iodine-deficient regions. Hypothyroidism.

  • May be considered for individuals who want a natural treatment
  • Not FDA-approved

Adverse effects

  • Side effects are similar to those for the synthetic 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 medications
  • Manufacturing and quality Quality Activities and programs intended to assure or improve the quality of care in either a defined medical setting or a program. The concept includes the assessment or evaluation of the quality of care; identification of problems or shortcomings in the delivery of care; designing activities to overcome these deficiencies; and follow-up monitoring to ensure effectiveness of corrective steps. Quality Measurement and Improvement control issues are common because of variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables hormone concentrations.

References

  1. T.A. (2013). A review of the pharmacokinetics of levothyroxine for the treatment of hypothyroidism. Touch Endocrinol. https://www.touchendocrinology.com/thyroid/journal-articles/a-review-of-the-pharmacokinetics-of-levothyroxine-for-the-treatment-of-hypothyroidism/
  2. Synthroid, Levoxyl (levothyroxine) dosing, indications, interactions, adverse effects, and more. (2021). MedScape. Retrieved August 3, 2021, from https://reference.medscape.com/drug/synthroid-levoxyl-levothyroxine-342732#11
  3. DrugBank Online. (2021). Levothyroxine: uses, interactions, mechanism of action. https://go.drugbank.com/drugs/DB00451
  4. American Thyroid Association. (2020). Thyroid hormone treatment. http://www.thyroid.org/thyroid-hormone-treatment/
  5. Ross, D.S. (2021). Treatment of primary hypothyroidism in adults. UpToDate. Retrieved July 31, 2021, from https://www.uptodate.com/contents/treatment-of-primary-hypothyroidism-in-adults
  6. Dong, B.J., Greenspan, F.S. (2012). Thyroid & antithyroid drugs. In: Katzung, B.G., Masters, S.B., Trevor, A.J. (Eds.), Basic & Clinical Pharmacology, 12th ed. McGraw-Hill Lange, pp. 681–696. https://pharmacomedicale.org/images/cnpm/CNPM_2016/katzung-pharmacology.pdf

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