Entecavir is an oral antiviral medicine used to treat chronic hepatitis B infection. It belongs to a class of medicines called nucleoside analog reverse transcriptase inhibitors, and is a well-established first-line option for suppressing hepatitis B virus replication. It is a prescription-only medicine.

• Therapeutic Class: Antiviral medicine for chronic hepatitis B.

• Pharmacological Class: Nucleoside analog reverse transcriptase inhibitor (a guanosine analog).

• Drug Family: Cyclopentyl guanine nucleoside analogs.

• ATC Classification: J05AF10 (Entecavir).

Approved: Chronic hepatitis B virus (HBV) infection in adults and pediatric patients 2 years of age and older with evidence of active viral replication and either persistent elevations in liver enzymes (ALT or AST) or histologically active liver disease.

Commonly used for: Patients with chronic hepatitis B needing long-term antiviral suppression, including those new to treatment (nucleoside-naive) and those with prior lamivudine treatment history.

Off-label use (only under medical guidance): Sometimes used in specific severe acute hepatitis B flare situations under specialist guidance, though its core approved use is chronic HBV infection.

• Oral tablets: 0.5 mg and 1 mg.

• Oral solution: 0.05 mg/mL, for patients unable to take tablets, including younger children.

Entecavir is converted inside cells to its active triphosphate form, which then interferes with the hepatitis B virus's reverse transcriptase enzyme at multiple steps needed for the virus to copy its genetic material. This blocks viral replication, helping suppress hepatitis B virus levels in the blood and reduce ongoing liver damage.

• Standard dose (treatment-naive adults/adolescents 16+): 0.5 mg taken orally once daily, on an empty stomach (at least 2 hours after a meal and 2 hours before the next meal).

• Condition-wise dose (lamivudine-refractory, known resistance substitutions, or decompensated liver disease): 1 mg taken orally once daily.

• Route: Oral, once daily, on an empty stomach for optimal absorption.

• Renal impairment: Dose interval or amount is adjusted based on creatinine clearance, including in patients on hemodialysis or peritoneal dialysis.

• Missed dose: Take as soon as remembered unless close to the next dose; don't double up.

• Overdose: No specific reported cases of overdose in trials; would be managed with supportive care and monitoring if it occurred.

• Common: Headache, fatigue, dizziness, and nausea.

• Serious: Lactic acidosis and severe hepatomegaly with steatosis (a rare but serious buildup of lactic acid with fatty liver enlargement), and severe acute exacerbation of hepatitis after stopping treatment.

• Emergency symptoms: Unusual muscle pain or weakness, rapid breathing, unusual tiredness (possible signs of lactic acidosis), or worsening jaundice/abdominal symptoms after stopping the medicine.

• Recovery advice: Liver function is monitored closely for several months after stopping entecavir, since hepatitis can flare significantly upon discontinuation; the medicine should never be stopped without medical guidance.

• Pregnancy: Used only if clearly needed, under medical guidance.

• Breastfeeding: Discussed with the treating doctor given limited safety data.

• Liver disease: This is the condition being treated; no dosage adjustment is necessary based on hepatic impairment alone (dose changes for decompensated disease relate to a different dosing tier, not liver function directly).

• Kidney disease: Requires dose interval or amount adjustment based on creatinine clearance.

• Elderly: Used with routine monitoring, with attention to kidney function given the dosing adjustments required for renal impairment.

• Children: Approved from 2 years of age, with weight-based dosing for nucleoside-naive and lamivudine-experienced pediatric patients weighing at least 10 kg.

• Other drugs affecting kidney function or cleared renally: may alter entecavir levels, given its renal elimination pathway; used with monitoring.

• Other hepatitis B or HIV nucleoside/nucleotide analogs: not typically combined given overlapping mechanisms, unless specifically directed for HIV/HBV coinfection management.

• Entecavir has relatively few major drug interactions, as it is not significantly metabolised by the liver's CYP450 enzyme system.

• Liver function tests (ALT, AST) periodically during treatment.

• Hepatitis B viral load (HBV DNA) periodically to monitor treatment response.

• Kidney function tests, particularly relevant to dose adjustment.

• Close hepatic monitoring for several months after stopping treatment, given the flare risk.

Tenofovir disoproxil fumarate, Tenofovir alafenamide (other first-line antivirals for chronic hepatitis B); Lamivudine, Adefovir, Telbivudine (older options, generally less preferred due to higher resistance rates).

Generally used as a standalone antiviral for chronic hepatitis B monotherapy; combination antiviral therapy is not typically standard for hepatitis B management with entecavir, in contrast to some other viral infections.

• Hepatitis B Medicines

• Nucleoside Analog Antivirals

• Chronic Liver Disease Treatments

1. Quick Facts About Hepatitis

2. What Is The Difference Between Hepatitis A, B, C, D, E?

3. Why Not All Viral Infections Need Antibiotics

• https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=046e61c9-9298-4b2e-b76e-b26b81fecd2

• https://pubmed.ncbi.nlm.nih.gov/16956310/

The information on this page is for educational purposes only and is not a substitute for medical advice. Please consult your doctor to know if this treatment is appropriate for your condition.