Famciclovir — what it treats and how to use it

Famciclovir is an antiviral most people hear about for shingles and genital herpes. It won’t cure herpes viruses, but it shortens outbreaks, eases pain, and helps sores heal faster. If you notice tingling, redness, or a rash starting, early treatment usually works best.

How famciclovir works and when to start

Famciclovir converts in your body to penciclovir, which stops the virus from copying itself. For shingles, start treatment within 72 hours of the rash for the biggest benefit. For genital herpes, take the medicine as soon as you feel the prodrome (that first tingle) or right after lesions appear. The earlier you start, the shorter and milder the outbreak tends to be.

Common adult regimens you might see: shingles often uses 500 mg three times daily for 7 days; episodic genital herpes has short-course options (for example, 125 mg twice daily for several days or other single-day high-dose regimens depending on the prescriber); suppressive therapy may use lower twice-daily doses. Your doctor will pick the dose based on the infection, your medical history, and kidney function.

Side effects, interactions, and safety tips

Most people tolerate famciclovir well. Typical side effects are headache, nausea, diarrhea, and tiredness. Serious problems are rare but can include allergic reactions or confusion, especially if your kidneys aren’t working well. Because famciclovir is cleared by the kidneys, dose adjustments are common for reduced kidney function — tell your provider if you have kidney disease.

Drug interactions are limited but real. Drugs that affect kidney clearance (or that raise penciclovir levels) can change how famciclovir behaves. Your pharmacist can check interactions for you. If you take other antivirals, antiretrovirals, or medicines that stress the kidneys, mention them before starting treatment.

Practical tips: take famciclovir exactly as prescribed, with or without food. Stay hydrated and rest during outbreaks. Avoid sex while lesions are present and until healed to lower transmission risk. Don’t stop a prescribed suppressive plan without talking to your doctor. If you get frequent or severe outbreaks, ask about long-term options and safety checks.

If you’re pregnant, breastfeeding, or have serious health issues, discuss risks and benefits with your provider — they’ll recommend the safest approach. If new or severe symptoms appear after starting famciclovir, call your healthcare team right away.

Want more on closely related meds like valacyclovir or acyclovir? Check with your clinic or pharmacist — some patients respond better to one antiviral than another, and small differences can matter for side effects, dosing, and convenience.