[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Hepatitis B antivirals](https://durgical.com/en/pharmacology/classes/hepatitis-b-antivirals/) › Entecavir [Pharmacology](https://durgical.com/en/pharmacology/) · [Hepatitis B antivirals](https://durgical.com/en/pharmacology/classes/hepatitis-b-antivirals/) # Entecavir An oral first-line antiviral for chronic hepatitis B. It strongly suppresses the virus; stopping it can cause a severe hepatitis flare. Updated 2026-11-01 - Class: [Hepatitis B antivirals](https://durgical.com/en/pharmacology/classes/hepatitis-b-antivirals/) - Enzyme: Hepatitis B virus polymerase (reverse transcriptase) - ATC code: J05AF10 - WHO Model List of Essential Medicines ✂**Hepatitis B virus polymerase (reverse transcriptase)**Entecavir ⓘ The figure shows entecavir triphosphate in HIV-1 reverse transcriptase (Q151M variant) bound to DNA, a related enzyme; no HBV polymerase structure with entecavir is available. **Target in 3D:** Hepatitis B virus polymerase (reverse transcriptase). PDB structure 5XN1 (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/5XN1) · Drag to rotate · pinch to zoom ## Mechanism of action Entecavir is a guanosine analogue. Cellular kinases convert it to entecavir triphosphate, which competes with dGTP and blocks all three activities of the HBV polymerase: base priming, reverse transcription of the negative DNA strand from pregenomic RNA, and synthesis of the positive DNA strand. Viral DNA in the blood falls sharply, but the cccDNA in liver cell nuclei remains. - Cellular kinases make entecavir triphosphate - Competes with dGTP at the HBV polymerase - Blocks priming, reverse transcription and positive-strand synthesis - HBV DNA falls; cccDNA in the nucleus remains ## Pharmacokinetics **Absorption** Oral, on an empty stomach (food reduces absorption) **Metabolism** Not a substrate, inhibitor or inducer of CYP450 enzymes **Elimination** Mostly unchanged in the urine (filtration and tubular secretion) **Half-life** Terminal 128 to 149 hours; effective accumulation half-life about 24 hours ## Indications - Chronic hepatitis B with active viral replication and raised transaminases or active liver disease, in adults and children from 2 years [Viral hepatitis →](https://durgical.com/en/conditions/viral-hepatitis/) ## Adverse effects ### Common - Headache - Fatigue - Dizziness - Nausea ### Serious (rare, important) - Severe acute hepatitis flare after stopping - Lactic acidosis and severe hepatomegaly with steatosis - HIV resistance if used in someone with untreated HIV ## Contraindications - None listed on the label apart from hypersensitivity ## Key interactions **Drugs that reduce kidney function or compete for tubular secretion** May raise entecavir levels or those of the other drug **Lamivudine-resistant HBV (rtM204I/V with or without rtL180M)** Lower susceptibility to entecavir; resistance appears more easily ## What is monitored - HBV DNA and liver tests during treatment - Liver tests for at least several months after stopping - HIV test before starting - Kidney function, especially in older people and transplant recipients ## Administration and safety - Oral, on an empty stomach: at least 2 hours after a meal and 2 hours before the next - Tablets and oral solution are interchangeable ## Nursing care - Teach not to stop the medicine without medical advice, because hepatitis can flare - Teach the empty-stomach timing - Teach to report jaundice, dark urine, abdominal pain, unusual tiredness or fast breathing - Remind that it does not prevent transmission; household contacts and sexual partners are vaccinated ## Pregnancy and breastfeeding Human data are insufficient to judge the risk; animal studies at usual exposures showed no harm. ## Memory aid EnteCAVir: «on an empty CAVity» (empty stomach) and never stopped without a plan. ## Test yourself Think of the answer, then tap the question to see it. ## Which three HBV polymerase activities does entecavir block? Priming, reverse transcription of the negative strand and synthesis of the positive DNA strand. ## How is entecavir taken in relation to meals? On an empty stomach, at least 2 hours after and 2 hours before a meal. ## Why is HIV status checked before starting entecavir? In someone with HIV who is not on full antiretroviral therapy, it can select HIV resistance. ## What may happen when entecavir is stopped? A severe acute hepatitis flare; liver tests are followed for months. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/entecavir/) ## Related drugs - [Lamivudine](https://durgical.com/en/pharmacology/lamivudine/) - [Tenofovir disoproxil](https://durgical.com/en/pharmacology/tenofovir-disoproxil/) ## Related conditions - [Viral hepatitis](https://durgical.com/en/conditions/viral-hepatitis/) [← Back to the class: Hepatitis B antivirals](https://durgical.com/en/pharmacology/classes/hepatitis-b-antivirals/) Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given. Sources: [DailyMed - ENTECAVIR tablet](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=92a5bebd-6408-463d-933c-bab8338a677e) (DailyMed (U.S. National Library of Medicine), 2026); [Hepatitis B](https://www.who.int/news-room/fact-sheets/detail/hepatitis-b) (World Health Organization, 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=J05AF10) (WHO Collaborating Centre for Drug Statistics Methodology, 2026); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/) (World Health Organization, 2025). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/entecavir/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/entecavir/