Acyclovir Auxilto Cream Mechanism of Action

Pharmacotherapeutic group: 13.1.4 - Medicines used to treat skin conditions. Anti-infective agents for topical application to the skin. Antiviral agents. ATC code: D06BB03.
Pharmacology: Pharmacodynamics: Acyclovir is an antiviral agent with high in vitro activity against the Herpes simplex (HSV) type I and II and Varicella-zoster viruses. Toxicity to mammalian host cells is low. After penetrating the cells infected by the Herpes simplex virus, acyclovir is phosphorylated to the active compound acyclovir triphosphate. The first step in this process is dependent on the presence of thymidine kinase, an enzyme encoded by the virus. Acyclovir triphosphate acts simultaneously as a substrate and an inhibitor of the viral DNA polymerase, preventing further synthesis of viral DNA without affecting normal cellular processes.
Acyclovir toxicity for non-infected mammalian host cells is low, since acyclovir cannot be used by mammalian thymidine kinase as a substrate.
Clinical studies with acyclovir cream have demonstrated statistically significant efficacy in healing of lesions and pain relief, compared to placebo. Healing time was 22% shorter in patients treated with acyclovir cream, compared to patients treated with placebo (average duration decreased by up to 0.5 days). Time to pain disappearance was reduced by approximately 20% (average duration decreased by up to 0.4 days). Approximately 60% of patients started treatment at an early stage (prodrome or erythema), with the remaining 40% starting treatment at a later stage (papular or vesicular stage).
Pharmacokinetics: Acyclovir absorption through the skin appears to be minimal following topical application to intact skin. The results of a study in several patients with localised infections by the Varicella-zoster virus have demonstrated that absorption through the skin is minimal when acyclovir cream is applied to the affected areas. Acyclovir distribution following topical application has not yet been determined. In vitro, acyclovir appears to be preferentially distributed to cells infected with the virus. Acyclovir metabolism following absorption through the skin has not been completely established. In a study involving topical application of acyclovir in patients with localised infections caused by the Varicella-zoster virus, 9.4% or less of the total daily dose of acyclovir was excreted unchanged in the urine.