Antiviral — Hepatitis B (Nucleoside Analogue) Pregnancy: Category C — consider continuing in pregnant women with high viral load to prevent vertical transmission. Switch to tenofovir disoproxil (preferred in pregnancy) if not already on it. Discuss risks/benefits with specialist.

Entecavir

Brand names: Baraclude

Adult dose

Dose: 0.5 mg once daily (treatment-naïve); 1 mg once daily (lamivudine-resistant or decompensated cirrhosis)

Route: Oral

Frequency: Once daily (on empty stomach — 2 hours before or after food)

Max: 1 mg/day

HBeAg-positive or -negative chronic HBV. Naïve patients: 0.5 mg daily. Lamivudine-resistant or decompensated cirrhosis: 1 mg daily. Take 2 hours before or 2 hours after food — food reduces bioavailability. Duration: often lifelong if cirrhotic; at least 12 months post-HBeAg seroconversion in non-cirrhotic. Source: BNF 90; EASL HBV Guidelines 2017.

Paediatric dose

Dose: Weight-based dosing (solution 0.05 mg/mL): 10–11 kg: 0.15 mg; 11–14 kg: 0.2 mg; 14–17 kg: 0.25 mg; 17–20 kg: 0.3 mg; 20–23 kg: 0.35 mg; 23–26 kg: 0.4 mg; 26–30 kg: 0.45 mg; >30 kg: 0.5 mg mg/kg

Route: Oral

Frequency: Once daily

Max: 0.5 mg/day

Licensed from 2 years of age, ≥10 kg, chronic HBV. Oral solution available. Source: BNF for Children 2024; EASL.

Dose adjustments

Renal

eGFR 30–49 mL/min: 0.25 mg daily (naïve) or 0.5 mg daily (resistant). eGFR 10–29 mL/min: 0.15 mg daily (naïve) or 0.3 mg daily (resistant). eGFR <10 mL/min or haemodialysis: 0.05 mg daily (naïve) or 0.1 mg daily (resistant) — administer after dialysis session.

Hepatic

No dose adjustment required for hepatic impairment — not CYP metabolised. Decompensated cirrhosis: use 1 mg dose (not 0.5 mg).

Paediatric weight-based calculator

Patient weight (kg)

Licensed from 2 years of age, ≥10 kg, chronic HBV. Oral solution available. Source: BNF for Children 2024; EASL.

Clinical pearls

Highest genetic barrier to resistance of all oral HBV antivirals: resistance rate <1% at 5 years in naïve patients (vs lamivudine >70% at 5 years). First-line preferred alongside tenofovir. EASL 2017 HBV guidelines recommend entecavir or tenofovir as monotherapy first-line.
HIV co-infection — critical safety rule: entecavir has intrinsic anti-HIV activity at HBV therapeutic doses. If used without fully suppressive HIV ART, can select the M184V mutation conferring high-level lamivudine/emtricitabine resistance in HIV — potentially compromising future HIV treatment options. Always use entecavir in HIV co-infection only when patient is on fully suppressive ART.
HBV flares on stopping: abrupt discontinuation causes viral rebound and hepatic decompensation — potentially fatal in cirrhotics. Never stop without specialist hepatologist review. Monitor LFTs and HBV DNA for 6 months after stopping.
Take on empty stomach: food reduces bioavailability by ~50%. Advise patients to take 2 hours before or 2 hours after meals consistently.
Lactic acidosis: rare but life-threatening class effect. Warn patients to report unexplained fatigue, myalgia, weakness, abdominal pain, or dyspnoea. Stop immediately if metabolic acidosis suspected. Source: BNF 90; EASL HBV Clinical Practice Guidelines 2017.

Contraindications

Hypersensitivity to entecavir
HIV co-infection NOT on fully suppressive ART: risk of selecting M184V mutation causing HIV resistance — CRITICAL

Side effects

Headache, fatigue, dizziness (mild — generally well tolerated)
Nausea, vomiting, diarrhoea
Elevated ALT (may be flare at treatment initiation or cessation)
Lactic acidosis and hepatomegaly with steatosis (rare — class effect of nucleoside analogues)
Alopecia (rare)

Interactions

HIV antiretrovirals (especially lamivudine, emtricitabine): HIV co-infection without ART — entecavir has anti-HIV activity at HBV doses and can select M184V mutation causing lamivudine/emtricitabine resistance in HIV — NEVER use as sole HBV treatment in HIV co-infection without fully suppressive ART
Renal toxins: additive nephrotoxicity risk — monitor eGFR

Monitoring

HBV DNA (at baseline, 12 weeks, then every 6 months — aim for undetectable)
HBeAg/anti-HBe serology (every 6 months — seroconversion may allow treatment discontinuation in non-cirrhotic)
Liver function tests (ALT, AST) every 3 months for first year, then 6-monthly
eGFR (at baseline and every 6 months — adjust dose if declining)
HBsAg annually (rare but HBsAg loss = functional cure)

Reference: BNFc; BNF 90; BNF for Children 2024; EASL Clinical Practice Guidelines HBV 2017; Chang et al. NEJM 2006 (entecavir phase III). Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways