Antivirals for Hepatitis B

Chemistry and Pharmacodynamics

Chemical structure

Antivirals for hepatitis B Hepatitis B Hepatitis B virus (HBV) is a partially double-stranded DNA virus, which belongs to the Orthohepadnavirus genus and the Hepadnaviridae family. Most individuals with acute HBV infection are asymptomatic or have mild, self-limiting symptoms. Chronic infection can be asymptomatic or create hepatic inflammation, leading to liver cirrhosis and hepatocellular carcinoma (HCC). Hepatitis B Virus have structures similar to those of nucleotides Nucleotides The monomeric units from which DNA or RNA polymers are constructed. They consist of a purine or pyrimidine base, a pentose sugar, and a phosphate group. Nucleic Acids and nucleosides Nucleosides Purine or pyrimidine bases attached to a ribose or deoxyribose. Nucleic Acids, thus they are classified as nucleoside/nucleotide analogs (also known as nucleoside/ nucleotide reverse transcriptase inhibitors Nucleotide Reverse Transcriptase Inhibitors Anti-HIV Drugs (NRTIs)).

• Nucleotide (nucleic acid + sugar + phosphate group Phosphate group Nucleic Acids) analogs of adenosine Adenosine A nucleoside that is composed of adenine and d-ribose. Adenosine or adenosine derivatives play many important biological roles in addition to being components of DNA and RNA. Adenosine itself is a neurotransmitter. Class 5 Antiarrhythmic Drugs:
  • Adefovir
  • Tenofovir Tenofovir An adenine analog reverse transcriptase inhibitor with antiviral activity against HIV-1 and hepatitis b. It is used to treat HIV infections and chronic hepatitis b, in combination with other antiviral agents, due to the emergence of antiviral drug resistance when it is used alone. Anti-HIV Drugs
• Nucleoside (nucleic acid + sugar) analogs of:
  • Cytidine → lamivudine Lamivudine A reverse transcriptase inhibitor and zalcitabine analog in which a sulfur atom replaces the 3′ carbon of the pentose ring. It is used to treat HIV disease. Anti-HIV Drugs
  • Guanosine → entecavir Entecavir Anti-HIV Drugs
  • Thymidine → telbivudine

Mechanism of action

• Disrupt viral DNA replication DNA replication The entire DNA of a cell is replicated during the S (synthesis) phase of the cell cycle. The principle of replication is based on complementary nucleotide base pairing: adenine forms hydrogen bonds with thymine (or uracil in RNA) and guanine forms hydrogen bonds with cytosine. DNA Replication
• Competitively inhibit viral RNA-dependent DNA polymerase RNA-dependent DNA polymerase An enzyme that synthesizes DNA on an RNA template. It is encoded by the pol gene of retroviruses and by certain retrovirus-like elements. Virology (also known as reverse transcriptase Reverse transcriptase A reverse transcriptase encoded by the pol gene of HIV. It is a heterodimer of 66 kda and 51 kda subunits that are derived from a common precursor protein. The heterodimer also includes an RNAse h activity that plays an essential role the viral replication process. HIV Infection and AIDS)
• Drug is intracellularly phosphorylated → incorporated into viral DNA DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA Types and Structure
• DNA DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA Types and Structure polymerization is blocked → chain termination

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

• Absorbed orally
• Tenofovir Tenofovir An adenine analog reverse transcriptase inhibitor with antiviral activity against HIV-1 and hepatitis b. It is used to treat HIV infections and chronic hepatitis b, in combination with other antiviral agents, due to the emergence of antiviral drug resistance when it is used alone. Anti-HIV Drugs:↑ 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 with high-fat meals
• Entecavir Entecavir Anti-HIV Drugs: delayed 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 with food

Distribution and metabolism

• Generally low protein binding
• Minor metabolism
• Intracellularly phosphorylated to active forms

Excretion

All of these medications are excreted by the 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

Chronic hepatitis B Hepatitis B Hepatitis B virus (HBV) is a partially double-stranded DNA virus, which belongs to the Orthohepadnavirus genus and the Hepadnaviridae family. Most individuals with acute HBV infection are asymptomatic or have mild, self-limiting symptoms. Chronic infection can be asymptomatic or create hepatic inflammation, leading to liver cirrhosis and hepatocellular carcinoma (HCC). Hepatitis B Virus

Indications for treatment:

• Without cirrhosis Cirrhosis Cirrhosis is a late stage of hepatic parenchymal necrosis and scarring (fibrosis) most commonly due to hepatitis C infection and alcoholic liver disease. Patients may present with jaundice, ascites, and hepatosplenomegaly. Cirrhosis can also cause complications such as hepatic encephalopathy, portal hypertension, portal vein thrombosis, and hepatorenal syndrome. Cirrhosis:
  • High viral load Viral load The quantity of measurable virus in a body fluid. Change in viral load, measured in plasma, is sometimes used as a surrogate marker in disease progression. HIV Infection and AIDS
  • Transaminitis Transaminitis Tick-borne Encephalitis Virus
• With cirrhosis Cirrhosis Cirrhosis is a late stage of hepatic parenchymal necrosis and scarring (fibrosis) most commonly due to hepatitis C infection and alcoholic liver disease. Patients may present with jaundice, ascites, and hepatosplenomegaly. Cirrhosis can also cause complications such as hepatic encephalopathy, portal hypertension, portal vein thrombosis, and hepatorenal syndrome. Cirrhosis:
  • Decompensation or acute liver failure Liver failure Severe inability of the liver to perform its normal metabolic functions, as evidenced by severe jaundice and abnormal serum levels of ammonia; bilirubin; alkaline phosphatase; aspartate aminotransferase; lactate dehydrogenases; and albumin/globulin ratio. Autoimmune Hepatitis
  • Compensated with a high viral load Viral load The quantity of measurable virus in a body fluid. Change in viral load, measured in plasma, is sometimes used as a surrogate marker in disease progression. HIV Infection and AIDS
  • Consider in compensated cirrhosis Cirrhosis Cirrhosis is a late stage of hepatic parenchymal necrosis and scarring (fibrosis) most commonly due to hepatitis C infection and alcoholic liver disease. Patients may present with jaundice, ascites, and hepatosplenomegaly. Cirrhosis can also cause complications such as hepatic encephalopathy, portal hypertension, portal vein thrombosis, and hepatorenal syndrome. Cirrhosis with elevated transaminases Transaminases A subclass of enzymes of the transferase class that catalyze the transfer of an amino group from a donor (generally an amino acid) to an acceptor (generally a 2-keto acid). Most of these enzymes are pyridoxyl phosphate proteins. Autoimmune Hepatitis
• Also indicated for concurrent:
  • Hepatocellular carcinoma Hepatocellular carcinoma Hepatocellular carcinoma (HCC) typically arises in a chronically diseased or cirrhotic liver and is the most common primary liver cancer. Diagnosis may include ultrasound, CT, MRI, biopsy (if inconclusive imaging), and/or biomarkers. Hepatocellular Carcinoma (HCC) and Liver Metastases
  • Hepatitis C Hepatitis C Hepatitis C is an infection of the liver caused by the hepatitis C virus (HCV). The infection can be transmitted through infectious blood or body fluids and may be transmitted during childbirth or through IV drug use or sexual intercourse. Hepatitis C virus can cause both acute and chronic hepatitis, ranging from a mild to a serious, lifelong illness including liver cirrhosis and hepatocellular carcinoma (HCC). Hepatitis C Virus infection
  • Need for immunosuppressive therapy

Differences among medications:

• Adefovir:
  • Helpful in lamivudine-resistant infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease
  • Preferably used in combination with another agent
• Tenofovir Tenofovir An adenine analog reverse transcriptase inhibitor with antiviral activity against HIV-1 and hepatitis b. It is used to treat HIV infections and chronic hepatitis b, in combination with other antiviral agents, due to the emergence of antiviral drug resistance when it is used alone. Anti-HIV Drugs: 
  • May be used as 1st-line for treatment-naive individuals
  • Effective as monotherapy
  • Helpful in lamivudine-resistant infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease
• Lamivudine Lamivudine A reverse transcriptase inhibitor and zalcitabine analog in which a sulfur atom replaces the 3′ carbon of the pentose ring. It is used to treat HIV disease. Anti-HIV Drugs:
  • Cheap
  • No longer 1st-line owing to high rates of resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing
  • An option for individuals with concurrent HIV HIV Anti-HIV Drugs
• Entecavir Entecavir Anti-HIV Drugs:
  • May be used as 1st-line for treatment-naive individuals
  • Effective as monotherapy
  • Low resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing rates; however, some cross resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing with lamivudine-resistant infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease
• Telbivudine:
  • Not available in the United States
  • High resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing rates
  • Unfavorable side-effect profile

HIV HIV Anti-HIV Drugs

• Most agents also active against HIV HIV Anti-HIV Drugs (exception: telbivudine)
• Of this group of medications, lamivudine Lamivudine A reverse transcriptase inhibitor and zalcitabine analog in which a sulfur atom replaces the 3′ carbon of the pentose ring. It is used to treat HIV disease. Anti-HIV Drugs is most likely to be used:
  • Can be used for treatment or prophylaxis Prophylaxis Cephalosporins
  • Used in some combination antiretroviral therapy Antiretroviral therapy Antiretroviral therapy (ART) targets the replication cycle of the human immunodeficiency virus (HIV) and is classified based on the viral enzyme or mechanism that is inhibited. The goal of therapy is to suppress viral replication to reach the outcome of undetected viral load. Anti-HIV Drugs

Adverse Effects and Contraindications

Adverse effects

• Nervous system Nervous system The nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system. Nervous System: Anatomy, Structure, and Classification:
  • Headache Headache The symptom of pain in the cranial region. It may be an isolated benign occurrence or manifestation of a wide variety of headache disorders. Brain Abscess
  • Fatigue Fatigue The state of weariness following a period of exertion, mental or physical, characterized by a decreased capacity for work and reduced efficiency to respond to stimuli. Fibromyalgia
  • Peripheral neuropathy Neuropathy Leprosy (telbivudine)
• GI symptoms:
  • 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
  • Abdominal pain Abdominal Pain Acute Abdomen
  • 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
• Musculoskeletal (particularly telbivudine):
  • Arthralgia Arthralgia Pain in the joint. Rheumatic Fever
  • Myalgia Myalgia Painful sensation in the muscles. Ion Channel Myopathy
  • Myopathy Myopathy Dermatomyositis
• Hepatic:
  • Lactic acidosis Lactic Acidosis Oxazolidinones (due to mitochondrial toxicity Toxicity Dosage Calculation)
  • Hepatomegaly with steatosis Steatosis Nonalcoholic Fatty Liver Disease
  • Hepatitis flare with discontinuation
• Other:
  • Cytopenias Cytopenias IPEX Syndrome
  • Nephrotoxicity Nephrotoxicity Glycopeptides (adefovir)

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 with caution in 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
• Entecavir Entecavir Anti-HIV Drugs should not be used in lamivudine-resistant infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease.

Drug interactions

• Telbivudine: ↑ toxicity Toxicity Dosage Calculation of interferon alfa Interferon Alfa Antivirals for Hepatitis C
• Medications that ↑ concentrations of tenofovir Tenofovir An adenine analog reverse transcriptase inhibitor with antiviral activity against HIV-1 and hepatitis b. It is used to treat HIV infections and chronic hepatitis b, in combination with other antiviral agents, due to the emergence of antiviral drug resistance when it is used alone. Anti-HIV Drugs:
  • Antivirals (e.g., acyclovir Acyclovir A guanosine analog that acts as an antimetabolite. Viruses are especially susceptible. Used especially against herpes. Herpes Zoster (Shingles), ganciclovir Ganciclovir An acyclovir analog that is a potent inhibitor of the herpesvirus family including cytomegalovirus. Ganciclovir is used to treat complications from aids-associated cytomegalovirus infections. Antivirals for Herpes Virus, cidofovir Cidofovir An acyclic nucleoside phosphonate that acts as a competitive inhibitor of viral DNA polymerases. It is used in the treatment of retinitis caused by cytomegalovirus infections and may also be useful for treating herpesvirus infections. Antivirals for Herpes Virus)
  • Aminoglycosides Aminoglycosides Aminoglycosides are a class of antibiotics including gentamicin, tobramycin, amikacin, neomycin, plazomicin, and streptomycin. The class binds the 30S ribosomal subunit to inhibit bacterial protein synthesis. Unlike other medications with a similar mechanism of action, aminoglycosides are bactericidal. Aminoglycosides

Mechanisms of Resistance

• Resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing tends to occur over time with long-term therapy.
• Resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing to NRTI therapy can occur via:
  • Genetic mutations Genetic Mutations Carcinogenesis in viral DNA DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA Types and Structure polymerase → conformational change → ↓ incorporation of drug into DNA DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA Types and Structure
  • Mutations allowing for a compensatory ↑ in viral replication
• This resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing is due to hepatitis B Hepatitis B Hepatitis B virus (HBV) is a partially double-stranded DNA virus, which belongs to the Orthohepadnavirus genus and the Hepadnaviridae family. Most individuals with acute HBV infection are asymptomatic or have mild, self-limiting symptoms. Chronic infection can be asymptomatic or create hepatic inflammation, leading to liver cirrhosis and hepatocellular carcinoma (HCC). Hepatitis B Virus’s:
  • ↑ Rate of replication
  • Lack of proofreading function
• Note: Many times, a nucleoside analog can be used for nucleotide analog resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing (and vice versa).