acyclovir vs entecavir
PlainMeds reviewed this comparison against our methodology in August 2026. It places FDA and CMS record fields side by side, without recommending either medication.
Side-by-side comparison of acyclovir and entecavir. Data from FDA drug databases (Orange Book, NDC Directory, recalls, shortages) covering 20,000+ approved drugs, plus CMS pricing; see our methodology.
Acyclovir is an antiviral medicine. It is used to treat infections caused by certain viruses.
Entecavir is a medicine used to treat chronic hepatitis B infection. It helps to lower the amount of the virus in your body.
Acyclovir is used to treat shingles, which is caused by herpes zoster. It also treats genital herpes, both the first time you have it and when it comes back. Acyclovir can also treat chickenpox.
Entecavir treats chronic hepatitis B virus (HBV) infection. It is for adults and children 2 years and older who have active virus and liver damage. The medicine can help reduce liver damage caused by the hepatitis B virus.
Acyclovir stops the virus from growing and spreading. It does this by interfering with the virus's ability to make copies of itself. This helps your body fight off the infection.
Entecavir belongs to a class of drugs called nucleoside analogs. It works by blocking an enzyme that the hepatitis B virus needs to multiply. This helps to lower the amount of virus in your body and improve your liver health.
- • Malaise (feeling unwell)
- • Nausea
- • Diarrhea
- • Headache
- • Tiredness
- • Dizziness
- • Nausea
- Fatigue 7,612
- Diarrhoea 7,064
- Pneumonia 5,471
- Nausea 5,328
- Pyrexia 4,719
- Death 539
- Drug Resistance 401
- Diarrhoea 363
- Fatigue 353
- Pyrexia 348
Acyclovir can cause nervous system problems, especially in older adults or people with kidney problems. Tell your doctor if you have kidney problems before taking this medicine.
Entecavir has the following warnings: * Stopping entecavir can cause a severe return of hepatitis B. Your liver function should be checked for several months after stopping. * If you have both HIV and hepatitis B, entecavir may make your HIV medicine less effective. Entecavir is not recommended if you have HIV and are not taking HIV medicine. * Entecavir can cause lactic acidosis (a buildup of acid in the blood) and severe liver problems. These can be fatal.
Tell your doctor if you are pregnant or plan to become pregnant. It is not known if acyclovir will harm an unborn baby. Talk to your doctor about the risks and benefits of taking acyclovir while breastfeeding.
Tell your doctor if you are pregnant or plan to become pregnant. There is a pregnancy registry to track outcomes in women who take entecavir during pregnancy. Talk to your doctor about the risks and benefits of taking entecavir while pregnant.
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How to Read This acyclovir vs entecavir Comparison
acyclovir is classified in the Antiviral (Nucleoside Analog) drug class, while entecavir sits within the Nucleoside Analog (HBV) class. Drugs from different classes work through distinct mechanisms, so a head-to-head comparison illustrates trade-offs rather than equivalence. Both drugs are prescription-only, so a licensed provider must authorize use.
Adverse event totals above are pulled from the FDA's Adverse Event Reporting System (FAERS). For these top-ranked reactions alone, acyclovir has 30,194 submissions while entecavir has 2,004. Those figures reflect cumulative reporting volume, not per-patient risk, so older, widely dispensed drugs typically look worse on count alone. No direct interaction between these two drugs is listed in our FDA-derived dataset, though co-prescription still warrants pharmacist review. Serious warnings, pregnancy guidance, and contraindications can differ even when indications overlap.
A table cannot represent individual circumstances. Data here is sourced from FDA Structured Product Labels (SPL) and FAERS, both of which update as manufacturers and clinicians submit new information. This registry does not provide medical, treatment, substitution, or medication-change directions for acyclovir or entecavir.
Registry boundary: This comparison displays source-record fields and does not provide individualized medical direction.