Entecavir

Guanosine nucleoside analogue, anti-HBV agent

ATC code: J05AF10 (Entecavir)

Brand names

Baraclude

Mechanism of action

Phosphorylated intracellularly to the active triphosphate. Competes with endogenous deoxyguanosine triphosphate for incorporation into nascent viral DNA. Suppresses three key HBV reverse transcriptase activities: priming, reverse transcription of pregenomic RNA and DNA-dependent DNA synthesis. Selectivity for HBV is high, anti-HIV activity is minimal (risk of HIV resistance selection in coinfected patients – monotherapy contraindicated). High barrier to resistance: monoresistance is rare in the first 5 years of therapy.

Indications

Chronic hepatitis B

First line

First-line therapy for chronic hepatitis B in adults with compensated or decompensated liver disease, naïve to nucleos(t)ide analogues. 2017 and the Spanish AEEH 2020 consensus position entecavir (0.5 mg/day) and tenofovir as equivalent first-line options in patients without lamivudine resistance. In lamivudine-resistant disease – switch to tenofovir rather than escalate entecavir. Therapy targets undetectable HBV-DNA and ALT normalisation; HBsAg seroconversion is rare.

Sources

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Official sources

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AEMPS / CIMA

Spanish Medicines Information Centre (CIMA)

Label dated: 08/13/2025

FDA / DailyMed

FDA — DailyMed Drug Labels

Label dated: 05/13/2026

Safety

Contraindications

Hypersensitivity to entecavir
Monotherapy in HIV-coinfected patients without effective ART (risk of selecting HIV resistance)

Serious adverse effects

Severe hepatitis B flare on abrupt discontinuation
Lactic acidosis and severe hepatomegaly with steatosis (NRTI class effect)
Anaphylactoid reactions (rare)

Common adverse effects

Headache
Fatigue
Nausea
Diarrhoea
Insomnia
Dizziness

PregnancyFDA C

FDA Category C. Pregnancy data are limited. Animal studies show teratogenicity at high doses. AEEH 2020 recommends switching pregnant patients from entecavir to tenofovir (Category B, larger pregnancy experience). When vertical HBV transmission risk is high (HBV-DNA above 200,000 IU/mL) – third-trimester antiviral therapy plus neonatal vaccination and HBIG.

Breastfeeding

Limited data. Hale L3. Excreted in animal milk; human data are scarce. EASL 2017 considers switching breastfeeding patients from entecavir to tenofovir (L2) or discontinuing breastfeeding. Decision individualised according to HBV activity.

Calculate RID

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

Frequently asked

What is Entecavir used for?

Entecavir is evaluated for the following indications with varying evidence strength: Chronic hepatitis B (evidence tier A). See the full indication matrix with dosing and citations above on this page.

What are the side effects of Entecavir?

Common side effects of Entecavir (≥ 1 in 100): Headache, Fatigue, Nausea, Diarrhoea, Insomnia, Dizziness. See the Safety section for uncommon and serious reactions.

Is Entecavir safe during pregnancy?

FDA category C. FDA Category C. Pregnancy data are limited. Animal studies show teratogenicity at high doses. AEEH 2020 recommends switching pregnant patients from entecavir to tenofovir (Category B, larger pregnancy experience). When vertical HBV transmission risk is high (HBV-DNA above 200,000 IU/mL) – third-trimester antiviral therapy plus neonatal vaccination and HBIG.

Is Entecavir compatible with breastfeeding?

Who should not take Entecavir?

Entecavir is contraindicated in: Hypersensitivity to entecavir; Monotherapy in HIV-coinfected patients without effective ART (risk of selecting HIV resistance). Full list in the Safety section.

Mechanism of action

Indications

Chronic hepatitis B

First line

Sources

Safety

Contraindications

Hypersensitivity to entecavir
Monotherapy in HIV-coinfected patients without effective ART (risk of selecting HIV resistance)

Serious adverse effects

Severe hepatitis B flare on abrupt discontinuation
Lactic acidosis and severe hepatomegaly with steatosis (NRTI class effect)
Anaphylactoid reactions (rare)

Common adverse effects

Headache
Fatigue
Nausea
Diarrhoea
Insomnia
Dizziness

PregnancyFDA C

Breastfeeding

Calculate RID

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

Frequently asked

What is Entecavir used for?

What are the side effects of Entecavir?

Common side effects of Entecavir (≥ 1 in 100): Headache, Fatigue, Nausea, Diarrhoea, Insomnia, Dizziness. See the Safety section for uncommon and serious reactions.

Is Entecavir safe during pregnancy?

Is Entecavir compatible with breastfeeding?

Who should not take Entecavir?

Entecavir is contraindicated in: Hypersensitivity to entecavir; Monotherapy in HIV-coinfected patients without effective ART (risk of selecting HIV resistance). Full list in the Safety section.