Aciclovir

Acyclovir is an antiviral medication used to treat infections caused by herpesviruses, principally herpes simplex virus types 1 and 2 (HSV-1, HSV-2) and varicella-zoster virus (VZV). It is available in oral tablets, topical cream, and intravenous formulations, and is used for both treatment and suppression of recurrent infections in some settings.

Acyclovir is a guanosine analogue that requires phosphorylation by viral thymidine kinase to become active. The active triphosphate form inhibits viral DNA polymerase and acts as a chain terminator when incorporated into viral DNA, limiting viral replication. This selective activation in infected cells helps limit effects on uninfected cells.

Pharmacokinetics and formulation notes: oral bioavailability is relatively low, typically around 10-20 percent, and the drug is more effectively delivered via prodrug forms such as valacyclovir. It is distributed widely in body tissues and fluids and is eliminated primarily by the kidneys through both glomerular filtration and tubular secretion, with a typical half-life of about 2–3 hours in individuals with normal renal function. Dose adjustments are needed in renal impairment.

Clinical use: oral acyclovir is commonly used for initial and recurrent HSV infections, including genital herpes, and for VZV infections such as shingles. Intravenous acyclovir is reserved for severe disease, immunocompromised patients, or serious infections like disseminated HSV or VZV. Topical acyclovir is sometimes used for mucocutaneous HSV lesions.

Safety and resistance: common side effects include nausea, diarrhea, and headache; intravenous therapy can cause phlebitis and nephrotoxicity at high doses. Resistance can occur with thymidine kinase mutations, especially in immunocompromised individuals. Acyclovir is generally considered safe in pregnancy when indicated.

History: Acyclovir was developed in the 1970s and has become a standard treatment for herpesvirus infections.