How long does Acyclovir Topical stay in your system?
Last updated September 7, 2026.
**Topical acyclovir barely enters your bloodstream, and the small amount that does is cleared within about a day of your last application.** Acyclovir cream and ointment are designed to act in the skin, so measured blood levels after topical use are low or undetectable. Any absorbed drug leaves through your kidneys, with a blood half-life of roughly 2 to 3 hours in adults with normal kidney function, which means about 12 to 15 hours to clear nearly all of it. Reduced kidney function slows that clearance, though the amounts involved with skin use remain very small. The medicine you apply stays on the surface until it soaks in or washes off, usually within a few hours. Wash your hands before and after each application, and finish the full course even if the sore starts to fade.
What to do
- Follow the dosing schedule: Cold sore cream is usually applied 5 times a day for 4 days, and the ointment 6 times a day for 7 days, so set reminders rather than guessing.
- Use a barrier: Apply with a cotton swab or finger cot when you can, and wash your hands before and after to avoid spreading virus to your eyes or others.
- Do not use it in your eyes: Skin products are not made for the eye, and eye pain, light sensitivity, or blurred vision needs same-day medical care.
- Tell your clinician about kidney problems: Reduced kidney function slows how fast acyclovir leaves your body, which matters more if you also take oral or IV antiviral doses.
- Know what topical cannot do: Cream and ointment shorten a local outbreak slightly but do not clear the virus from your body or prevent future episodes.
- Ask about pills for frequent outbreaks: If sores keep coming back or cover a wide area, oral antivirals are usually more effective than a topical product.
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