Antivirals
Also known as: antiviral drugs, antiviral agents
Antivirals are medications that inhibit the replication of viruses inside host cells. Unlike antibiotics, they generally suppress viral reproduction rather than destroying the virus outright, so they work best when started early in an infection.
Viruses replicate using the host cell's own machinery, which makes selective toxicity harder to achieve than with bacteria. Antivirals solve this by targeting steps unique to the viral life cycle: attachment and entry, uncoating, genome replication by viral polymerases, integration, protein cleavage by viral proteases, and release of new particles. Most agents are virustatic — they halt replication and let the immune system clear the remaining virus — which is why immunocompromised patients respond less completely.
Several drug classes recur across therapy. Nucleoside analogs such as acyclovir and valacyclovir treat herpes simplex and varicella-zoster; acyclovir is activated by viral thymidine kinase, concentrating its effect in infected cells, while ganciclovir covers cytomegalovirus. Neuraminidase inhibitors such as oseltamivir and zanamivir shorten influenza when started within about 48 hours of symptom onset. HIV treatment combines agents from different classes — nucleoside and non-nucleoside reverse transcriptase inhibitors, protease inhibitors, and integrase inhibitors — because combination therapy suppresses viral load while limiting resistance. Direct-acting antivirals have made most chronic hepatitis C infections curable.
Class-specific monitoring matters. Acyclovir can crystallize in renal tubules, so adequate hydration and dose adjustment for renal function are standard; ganciclovir suppresses the bone marrow; protease inhibitors carry substantial drug-drug interaction risk through cytochrome P450 metabolism. Adherence is critical: skipped doses in HIV or hepatitis regimens promote resistant strains. Pharmacy staff also handle practical requirements — refrigerated storage for some suspensions, correct reconstitution of oseltamivir suspension, and inventory control for high-cost specialty antivirals.
The PTCE covers antivirals within antimicrobials by organ system, expecting you to match brand and generic names, recognize dosage forms and storage requirements, and understand inventory handling for these products. USMLE Step 1 pharmacology focuses instead on mechanism of action, activation requirements, resistance mechanisms, and characteristic adverse effects.
Key takeaways
- Antivirals interrupt specific stages of viral replication rather than killing the virus directly.
- Most are virustatic, so early initiation and an intact immune response improve outcomes.
- Major classes include nucleoside analogs, neuraminidase inhibitors, and the reverse transcriptase, protease, and integrase inhibitors used in HIV therapy.
- Adherence and combination therapy limit resistance, and several agents require renal dosing or interaction monitoring.