Antiherpetic agents

Antivirals

Aciclovir

Valacyclovir

• Guanosine analogue (nucleoside analogue)

• HSV/VZV-coded thymidine kinase monophosphorylates the guanosine analogue to an active intermediate → phosphorylation by cellular kinases → acyclovir triphosphate (ACV-TP)

• The phosphorylated drug is incorporated into the replicating viral DNA strand → inhibition of viral DNA polymerase via chain termination

• Selective action in infected cells only with minimal effect on host cells → fewer side effects

• Active infection (not effective against latent infections )

  • Herpes simplex

    • Systemic: HSV encephalitis, and genital herpes

    • Topical: early genital and mucocutaneous herpes

  • Varicella zoster: (e.g., active shingles) treated with systemic acyclovir, especially in immunocompromised adults

  • EBV (weak activity)

• Prophylaxis in immunodeficient and immunocompetent individuals with recurring or severe infections

• No effect on CMV (lacks thymidine kinase needed to activate the guanosine analogue)

• Acyclovir

  • Obstructive crystal-induced nephropathy

  • Acute kidney injury

  • Both can be prevented by adequate hydration and dosage adjustment

• Thrombotic thrombocytopenic purpura

• Gastrointestinal symptoms (e.g., nausea)

• ↑ Transaminases

• Mutation of viral thymidine kinase