Famciclovir

1 medicine

Famciclovir is an antiviral that treats cold sores, genital herpes and shingles. People with reduced kidney function need a lower dose, because the drug builds up in the body and can affect the nervous system.

Famvir

Famciclovir

250/500mg

Famvir is a antivirals medication containing Famciclovir, available as 250/500mg tablets.

from $2.34 / tablet View

Key facts

  • Famciclovir is an antiviral tablet used for cold sores, genital herpes and shingles (herpes zoster). It works by stopping the herpes virus from copying its DNA.
  • Start it as soon as symptoms appear, ideally within 48 to 72 hours of a shingles rash or a genital herpes outbreak, for the best effect.
  • Your kidneys clear famciclovir from the body, so anyone with reduced kidney function needs a lower dose to avoid a buildup.
  • Seek urgent care for a widespread rash with fever, or shingles affecting the eye or the tip of the nose.

What famciclovir treats

Famciclovir treats infections caused by herpes simplex virus and varicella-zoster virus. It shortens outbreaks and speeds healing in cold sores (herpes labialis), genital herpes, and shingles, and can be taken regularly to reduce how often genital herpes recurs. It does not cure the underlying infection; the virus stays dormant in nerve tissue between outbreaks.

How famciclovir works

Once absorbed, famciclovir is converted in the body to penciclovir, its active form. Cells infected with herpes virus convert penciclovir further into a form that blocks the viral enzyme responsible for copying viral DNA. This stops the virus multiplying inside infected cells, so your immune system can clear the outbreak faster and fewer new lesions form.

Before you take it

  • Tell your prescriber if you have kidney disease. Your dose needs to be reduced, and severe kidney impairment may rule the drug out.
  • Mention pregnancy or breastfeeding; famciclovir is used only if the expected benefit outweighs the risk.
  • Confirm you don't have an allergy to famciclovir or penciclovir before starting.
  • Drink enough fluids while taking it, particularly if your kidney function is already reduced.

Side effects

Common effects include headache, nausea, diarrhea and dizziness, and usually pass as treatment finishes.

Stop and seek urgent medical care for any of these:

  • A severe skin rash, blistering, or peeling skin.
  • Signs of a serious allergic reaction: swelling of the face or throat, or difficulty breathing.
  • Confusion, hallucinations or unsteady movements, which can occur at high doses in people with kidney problems.

Safety essentials

  • Dose adjustment for kidney function is not optional. An unadjusted dose in someone with impaired kidneys can build up and cause toxicity affecting the nervous system.
  • Famciclovir does not prevent transmission of genital herpes to a partner; use condoms and avoid contact during an active outbreak.
  • Complete the full course even if symptoms improve early, so the outbreak is properly controlled.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.