Antivirals treat viral infections by acting on different stages of the viral replication cycle. Aciclovir (nucleoside analogue — activated by viral thymidine kinase, inhibits viral DNA polymerase) is the drug of choice for Herpes simplex and Varicella-zoster infections. Foscarnet (phosphonate — direct DNA polymerase inhibition) is an alternative for aciclovir-resistant strains. Neuraminidase inhibitors (oseltamivir, zanamivir) block release of new viral particles in influenza infections. Ribavirin (broad-spectrum nucleoside analogue) is used in hepatitis C in combination with direct-acting antivirals. Unlike antibacterials, they act inside host cells, often with selectivity dependent on viral enzymes. (Sources: DailyMed/FDA, EMC-UK/MHRA, Health Canada)
