Two medicines, side by side
Acyclovir vs entecavir
Acyclovir is labeled for herpes and shingles; entecavir for hepatitis b. Their labels share no use, so they are not alternatives to each other. Drugs@FDA records approvals of acyclovir since 1982 and of entecavir since 2005. Pharmacies paid $0.0962 per acyclovir 400 mg tablet and $0.219 per entecavir 0.5 mg tablet (NADAC, October 7, 2026); the strengths differ, so the two prices are not like for like. In FDA's classes, acyclovir is a herpes zoster virus nucleoside analog dna polymerase inhibitor and entecavir a hepatitis b virus nucleoside analog reverse transcriptase inhibitor.
Check it at the source: the acyclovir FDA label on DailyMed (effective July 24, 2026); the entecavir FDA label on DailyMed (effective November 6, 2019).
Highlights of the acyclovir record
Acyclovir (Zovirax) · label of July 24, 2026
Used for
From the label: indicationsHerpes Zoster Infections: Acyclovir tablets are indicated for the acute treatment of herpes zoster (shingles). Genital Herpes: Acyclovir tablets are indicated for the treatment of initial episodes and the management of recurrent episodes of genital herpes. Chickenpox: Acyclovir tablets are indicated for the treatment of chickenpox (varicella).
On the market
- Earliest approval on file
- March 29, 1982
- Generic labelers
- 66 labelers
- Pharmacy cost
- $0.0962 per tablet
Supply and safety
- Shortage
- No current entry
- Recalls
- 12
Highlights of the entecavir record
Entecavir (Baraclude) · label of November 6, 2019
SEVERE ACUTE EXACERBATIONS OF HEPATITIS B, PATIENTS CO-INFECTED WITH HIV AND HBV, and LACTIC ACIDOSIS AND HEPATOMEGALY Severe acute exacerbations of hepatitis B have been reported in patients who have discontinued anti-hepatitis B therapy, including entecavir. Hepatic function should be monitored closely with both clinical and laboratory follow-up for at least several months in patients who discontinue anti-hepatitis B therapy.
Used for
From the label: indicationsBARACLUDE ® (entecavir) is indicated for the treatment of chronic hepatitis B virus infection in adults and pediatric patients 2 years of age and older with evidence of active viral replication and either evidence of persistent elevations in serum aminotransferases (ALT or AST) or histologically active disease. […]
On the market
- Earliest approval on file
- March 29, 2005
- Generic labelers
- 15 labelers
- Pharmacy cost
- $0.219 per tablet
Supply and safety
- Shortage
- No current entry
- Recalls
- 5
Source: FDA drug labels via openFDA (Acyclovir label of July 24, 2026, Entecavir label of November 6, 2019); NDC Directory, Drugs@FDA, NADAC, FDA shortages and recalls (October 8, 2026)
How do acyclovir and entecavir differ on the record?
In FDA's classes, acyclovir is a herpes zoster virus nucleoside analog dna polymerase inhibitor and entecavir a hepatitis b virus nucleoside analog reverse transcriptase inhibitor.
Half-life, in each label's words: Acyclovir, “Mean half-life after oral doses of 300 mg/m 2 and 600 mg/m 2 in pediatric patients aged 7 months to 7 years was 2.6 …”; Entecavir, “After reaching peak concentration, entecavir plasma concentrations decreased in a bi-exponential manner with a terminal …”
Only the entecavir label carries a boxed warning.
Generics: acyclovir since 1997; entecavir since 2014 (Drugs@FDA).
| Acyclovir | Entecavir | |
|---|---|---|
| Labeled for | Herpes and shingles | Hepatitis B |
| Pharmacologic class | Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitor, Herpes Zoster Virus Nucleoside Analog DNA Polymerase Inhibitor, Herpesvirus Nucleoside Analog DNA Polymerase Inhibitor | Hepatitis B Virus Nucleoside Analog Reverse Transcriptase Inhibitor |
| How it works (label) | n/a | Entecavir is an antiviral drug against hepatitis B virus [see Microbiology (12.4) ]. |
| Half-life (label) | Mean half-life after oral doses of 300 mg/m 2 and 600 mg/m 2 in pediatric patients aged 7 months to 7 years was 2.6 hours (range 1.59 to 3.74 hours). | After reaching peak concentration, entecavir plasma concentrations decreased in a bi-exponential manner with a terminal elimination half-life of approximately 128–149 hours. |
| Earliest approval on file (Drugs@FDA) | March 29, 1982 | March 29, 2005 |
| First generic approved | April 22, 1997 | August 26, 2014 |
| Generic labelers (NDC) | 66 labelers | 15 labelers |
| Pharmacy cost (NADAC, each one's most listed form; strengths differ) | $0.0962 per tablet (Acyclovir 400 mg tablet) | $0.219 per tablet (Entecavir 0.5 mg tablet) |
| 12-month price change | +5% | -17% |
| Boxed warning | No | Yes |
| Shortage now | No current entry | No current entry |
| Recalls recorded | 12 | 5 |
| FAERS reports (a report is not proof of cause; counts follow how widely a medicine is used) | 114,717 | 11,608 |
| DEA schedule | none | none |
Source: Drugs@FDA, FDA NDC Directory, CMS NADAC of October 7, 2026, FDA shortages and recalls, FAERS via openFDA (FDA files October 8, 2026)
What next?
- Alternatives to acyclovir
- every medicine labeled for the same conditions