What side effects can acyclovir cause?
Acyclovir can cause side effects in some people. Commonly reported effects include nausea, diarrhea, headache, and feeling tired. Some people also report dizziness and rash.
What are the more serious acyclovir side effects to watch for?
Seek urgent medical help if you develop signs of a serious allergic reaction, such as swelling of the face or throat, trouble breathing, or hives. Also get prompt care if you have severe or persistent vomiting, confusion, or marked changes in urination.
Does the risk of side effects change with the dose or how it’s taken?
Yes. Side effects can be more likely or more intense with higher doses and with intravenous (IV) use compared with tablets or topical forms. Kidney-related problems are a key concern especially with IV acyclovir and in people who already have kidney impairment or dehydration.
Who is more likely to get side effects from acyclovir?
Risk is higher in people with reduced kidney function, older adults, and people who are dehydrated. Drug–drug interactions can also matter, especially if acyclovir is taken with other medications that affect kidney function.
What should patients do if they miss a dose?
For oral acyclovir, take the missed dose when you remember unless it’s close to the next scheduled dose. Do not take a double dose.
When should patients stop acyclovir and contact a clinician?
Contact a clinician promptly if you notice new rash, persistent vomiting, severe headache, confusion, or major changes in urination. Stop only if you have symptoms of a serious allergic reaction or if a clinician tells you to.
Are there safer alternatives if acyclovir isn’t tolerated?
Clinicians sometimes switch to other antiviral options depending on the condition being treated (for example, valacyclovir or famciclovir for many herpes infections). The best choice depends on kidney function, the specific infection, and your treatment history.
Sources
I don’t have any provided source material in this chat to cite specific side-effect details for acyclovir. If you share a link or text you’re using (or tell me the formulation: oral tablets, topical cream, or IV), I can produce a sourced, tightly accurate side-effect description from it.