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Famciclovir is an oral prodrug of penciclovir used for shingles, genital herpes and cold sores; the benefit depends heavily on starting it within the first 48 hours of symptoms.
- Shortens an outbreak when started within 48 hours
- Covers shingles, genital herpes and cold sores
- Activated preferentially inside the infected cells themselves
- Longer dosing interval than aciclovir, fewer daily doses
- Worth keeping a supply ready before an outbreak
- Oral prodrug of penciclovir, no cream required
Mechanism
It is deacetylated and oxidised in gut wall and liver to penciclovir, which herpesvirus thymidine kinase phosphorylates preferentially inside infected cells before cellular kinases complete the triphosphate. That triphosphate competes with dGTP at the viral DNA polymerase; its intracellular half life is roughly ten times longer than aciclovir triphosphate, which is why the dosing interval can be longer.
Safetyrisks and cautions, not medical advice
requires dose reduction in kidney impairment and is only useful if started within the first day or two of an outbreak, so it needs a diagnosis rather than speculative use
Subjective profileweighing the evidence above
Timing decides whether this is worth anything at all; begun inside the first day or two of an outbreak it shortens matters meaningfully, and begun on day four it is an expensive placebo. That makes it one of the few drugs where already having a supply in the cupboard is the sensible pattern, which is exactly how people with diagnosed recurrent herpes are prescribed it. The diagnosis has to come first though, and shingles in particular deserves eyes on it from someone who can spot ophthalmic involvement. Kidney impairment calls for a reduced amount, and that is a calculation rather than a guess.
Where to buy
Suppliers
Vendors carrying Famciclovir, with live product details and codes. Links are affiliate links that support the wiki at no cost to you.
RUPharma🌐
Famciclovir