Does acyclovir expire?
The printed date covers the sealed pack. Once acyclovir is opened, mixed or diluted, its label sets a second and usually much shorter limit — quoted below, per product.
Shortest limit on any acyclovir label: 24 hours
“Once diluted for administration, each dose should be used within 24 hours.”
That applies to the product it is printed on, not to every form of acyclovir — check which one you have against the list below.
What the labels say
“Once diluted for administration, each dose should be used within 24 hours.”
On the label for Acyclovir Sodium · DailyMed
How the label says to keep acyclovir
Storage is the other half of the question: the stability behind any date assumes these conditions, and a medicine kept outside them ages faster than the calendar says.
- “Store at 20° to 25°C (68° to 77°F).”
- “Protect from moisture.”
- “Store at 20° to 25°C (68° to 77°F) [See USP Controlled Room Temperature] and protect from light and moisture.”
- “Store at 20° to 25°C (68° to 77°F); excursions permitted between 15° to 30°C (59° to 86°F).”
- “Store between 15º and 25ºC.”
- “Protect from light and moisture.”
- “Store at 20° to 25°C (68° to 77°F) [See USP Controlled Room Temperature].”
- “16 HOW SUPPLIED/STORAGE AND HANDLING Each gram of Acyclovir Cream contains 50 mg (equivalent to 5% w/w) of acyclovir in an aqueous cream base.”
Frequently asked questions
Does acyclovir expire?
Two different clocks apply and only one of them is the printed date. The date on a sealed pack is the manufacturer's guarantee for the unopened product. Once it is opened, mixed or diluted, the label imposes its own limit — as tight as 24 hours on some acyclovir products, and that is the number quoted on this page.
Can I still use acyclovir after the date on the box?
This page cannot tell you that, and nor can any page. The FDA's own shelf-life programme found 88% of tested lots stayed within specification at least a year past expiry — and concluded in the same breath that lot-to-lot variation means this can only be confirmed by testing each lot. What you can check at home is the in-use limit above and whether the product has been stored as the label requires. Ask a pharmacist about a specific pack; they will also dispose of what you no longer need.
Why do different acyclovir products have different limits?
Because they are different formulations. A suspension that gets mixed with water, a pen that gets carried at room temperature, and a sealed tablet do not behave alike, so each manufacturer's label sets its own limit and each is shown here with the product it belongs to. We never merge them into one number for the molecule.
More on acyclovir
Quoted from FDA labels for reference, not medical advice, and not a suggestion to use anything past its limit. If you are unsure whether a pack is still good, a pharmacist can tell you and can dispose of it safely.