18.03.2 Drugs used to Treat the Herpesvirus

The main drug used to treat the DNA virus, herpesvirus is aciclovir. Aciclovir is a prodrug. It is converted by viral enzymes to aciclovir triphosphate, which inhibits viral DNA polymerase. Thus, aciclovir acts by inhibiting the replication of viral DNA. As it needs the viral enzyme to be converted to the active form, the selective toxicity of aciclovir is due to it being selectively ‘activated” in infected cells.

Aciclovir is very good against herpes simplex (which causes cold sores, conjunctivitis, mouth ulcers, genital infections, encephalitis). Herpes simplex is more susceptible to aciclovir than other herpesviruses such as varicella zoster (which causes chickenpox, shingles).

Aciclovir can be used orally, but only has about a 20% bioavailability. Aciclovir can also be used intravenously or topically. Fortunately, the unwanted effects with aciclovir are minimal, espscially when it is used topically (eg for cold sores).