Most Common Side Effects of Famciclovir
Famciclovir, used to treat herpes zoster (shingles) and genital herpes, commonly causes headache (up to 18% of patients), nausea (up to 9%), and diarrhea (up to 7%). Other frequent effects include abdominal pain, fatigue, dizziness, and vomiting, each affecting 2-4% of users in clinical trials.[1][2]
How Side Effects Differ by Condition Treated
In shingles treatment, headache tops the list at 17.6%, followed by nausea (7.7%) and diarrhea (4.5%). For genital herpes suppression, rates drop slightly: headache (13%), nausea (4.8%), and diarrhea (4%). These vary by dose and duration, with higher incidences in short-term high-dose regimens.[1][2]
Serious but Less Common Risks
Rarely, famciclovir leads to severe reactions like thrombocytopenia (low platelets), hallucinations, or seizures, especially in those with kidney issues. Allergic responses including rash, itching, or swelling occur in under 1%. Monitor kidney function, as the drug metabolizes to penciclovir, which relies on renal clearance.[1][3]
Who Experiences Side Effects Most
Elderly patients or those with reduced kidney function report higher rates of nausea and dizziness. Women note slightly more gastrointestinal issues than men. Most effects are mild and resolve after stopping treatment.[2]
Famciclovir vs. Acyclovir and Valacyclovir
Famciclovir has a similar profile to valacyclovir (headache, nausea primary) but fewer dosing requirements. Acyclovir causes more nausea (15-20%) and less headache. All three share risks like renal toxicity at high doses.[1][3]
[1]: Famciclovir Prescribing Information (FDA)
[2]: Famciclovir Clinical Trial Data (Drugs.com)
[3]: MedlinePlus - Famciclovir