Famciclovir (Famvir) has the same mechanisms of action as acyclovir. It is a pro-drug of penciclovir and is a functional equivalent to acyclovir and valacyclovir. It has a relatively long intracellular half-life of seven to 10 hours. The main advantage of famciclovir is that it is used only three times a day (instead of the five times a day dosage of acyclovir), and it has been shown to decrease the duration and severity of post-herpetic neuralgia. It is active against herpes simplex and varicella. It can be taken without regard to meals, and is metabolized by the kidneys. This is true for all the oral antivirals, therefore, in patients with kidney disease, consultation with the patient's kidney doctor or a pharmacist is mandatory to prescribe the proper dosage in the setting of compromised renal function.
Persons who are on drugs which suppress the immune system are more susceptible to infections than healthy individuals. Chicken pox and measles , for example, can have a more serious or even fatal course in non-immune children or adults on corticosteroids. In such children or adults who have not had these diseases particular care should be taken to avoid exposure. How the dose, route and duration of corticosteroid administration affects the risk of developing a disseminated infection is not known. The contribution of the underlying disease and/or prior corticosteroid treatment to the risk is also not known. If exposed, to chicken pox, prophylaxis with varicella zoster immune globulin (VZIG) may be indicated. If exposed to measles, prophylaxis with pooled intramuscular immunoglobulin (IG) may be indicated. (See the respective package inserts for complete VZIG and IG prescribing information.) If chicken pox develops, treatment with antiviral agents may be considered. Similarly, corticosteroids should be used with great care in patients with known or suspected Strongyloides (threadworm) infestation. In such patients, corticosteroid-induced immunosuppression may lead to Strongyloides hyperinfection and dissemination with widespread larval migration, often accompanied by severe enterocolitis and potentially fatal gram-negative septicemia .