What viruses does famciclovir target?
Famciclovir treats herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2), which cause oral and genital herpes. It also works against varicella-zoster virus (VZV), responsible for chickenpox and shingles.[1]
How does famciclovir work against these viruses?
Famciclovir converts to penciclovir inside infected cells. Penciclovir blocks viral DNA polymerase, halting replication of HSV-1, HSV-2, and VZV. It requires viral thymidine kinase for activation, so it spares healthy cells.[1][2]
Which herpes viruses does it cover specifically?
- HSV-1: Cold sores, oral herpes.
- HSV-2: Genital herpes outbreaks.
- VZV: Shingles (herpes zoster) and chickenpox prevention in certain cases.
It does not treat other herpesviruses like cytomegalovirus (CMV) or Epstein-Barr virus (EBV).[1]
Does it work against other virus families?
No. Famciclovir has no activity against non-herpesviruses such as influenza, HIV, hepatitis B/C, or respiratory syncytial virus (RSV). It's specific to alphaherpesviruses (HSV) and varicella-zoster.[2]
When is famciclovir used for each virus?
| Virus | Common Uses |
|-------|-------------|
| HSV-1/HSV-2 | Acute outbreaks, suppression therapy for recurrent genital herpes, treatment of herpes labialis.[1] |
| VZV | Shingles rash and pain (zoster), acute chickenpox in immunocompromised patients.[1][3] |
Dosing varies: 250-500 mg three times daily for herpes zoster; 125-250 mg twice daily for suppression.[3]
What if someone has a different herpesvirus like CMV?
Famciclovir fails against CMV, HHV-6, or HHV-8. Alternatives include ganciclovir or valganciclovir for CMV.[2]
Limitations and resistance concerns
Resistance occurs in immunocompromised patients via thymidine kinase mutations, especially with prolonged use. Cross-resistance exists with acyclovir. Test susceptibility if treatment fails.[1][2]
Sources:
[1] FDA Label for Famvir (famciclovir)
[2] Medscape - Famciclovir Overview
[3] Drugs.com - Famciclovir Uses