Famciclovir

How it works

It is converted to penciclovir, which is phosphorylated by viral thymidine kinase and then host kinases to a triphosphate that inhibits viral DNA polymerase and DNA replication.

Prescribing in practice

• Treatment of herpes zoster is most effective when started as early as possible after rash onset, so prompt initiation is the priority.
• Dose adjustment is required in renal impairment because penciclovir is renally cleared.
• It does not eradicate latent virus, so recurrences can still occur after treatment.

Monitoring

Routine laboratory monitoring is not usually required, but assess renal function in those at risk and review clinical response.

Counselling the patient

• Start treatment as soon as possible after symptoms or rash begin.
• Maintain good fluid intake, particularly if you have kidney problems.
• This treats outbreaks but does not cure the underlying infection, which may recur.

Evidence & guidelines

Famciclovir is an established oral option for herpes zoster and herpes simplex in UK clinical guidance, comparable to other guanine-analogue antivirals.