Viruses hijack host cells, so drugs must interrupt that process carefully. An antiviral is a medication designed to inhibit the replication or spread of viruses inside the body.

Available agents target specific viruses or viral families—herpesviruses, influenza, HIV, hepatitis B and C, and others. Mechanisms include blocking entry, inhibiting viral enzymes, or preventing release of new particles. Because viruses mutate rapidly, resistance can emerge and combination therapy is sometimes required.

Antivirals work best when started early in infection or used prophylactically in high-risk patients. They do not replace vaccination where effective vaccines exist. Research continues to expand the short list of viruses for which reliable drugs are available.

• Medication that inhibits viral replication or spread
• Usually virus-specific or family-specific
• Most effective when given early or preventively
• Resistance can develop, sometimes requiring combinations