Practical information on using guanine analogues

The guanine analogues aciclovir, famciclovir and valaciclovir are active against herpes simplex and varicella-zoster viruses. Aciclovir is poorly and erratically absorbed after oral administration, and even less so after topical administration. Valaciclovir, a prodrug of aciclovir, and famciclovir are well absorbed after oral administration; they are dosed less frequently than aciclovir.

In Australia, valaciclovir is not licensed for use in children younger than 12 years; however, it is licensed internationally for use in younger children (older than 2 years). Famciclovir is not used in children.

Ganciclovir is used intravenously for the treatment of cytomegalovirus (CMV) infection. It causes bone marrow suppression, which is dose dependent. For immediately sight-threatening CMV retinitis, ganciclovir may be used intravitreally in combination with systemic antiviral therapy.

Valganciclovir, a prodrug of ganciclovir, is well absorbed when taken orally; it is then hydrolysed to ganciclovir. Oral valganciclovir has been shown to be equally effective to intravenous ganciclovir in some settings, but has not been studied in all situations. Valganciclovir is also used for CMV prophylaxis in immunocompromised adults without HIV infection.

For information on monitoring plasma concentrations of guanine analogues, see Monitoring antiviral blood concentrations.