Antivirals

Antivirals are medications used to treat viral infections by inhibiting viral replication or inactivating virions. They are generally virus- or family-specific rather than broadly active against all pathogens, and their effectiveness often depends on early administration. Antiviral therapy can be used for treatment or prevention in high-risk settings.

Most antivirals target particular stages of the viral life cycle. Nucleoside or nucleotide analogs resemble natural building blocks and terminate viral nucleic acid synthesis (for example, acyclovir for herpesviruses, sofosbuvir for hepatitis C). Polymerase inhibitors block viral RNA or DNA synthesis, while neuraminidase inhibitors reduce release of influenza viruses (oseltamivir, zanamivir). Protease inhibitors prevent maturation of viral proteins, notably in HIV therapy. Other agents include entry inhibitors and monoclonal antibodies that block infection or neutralize viruses. Some agents have broader activity against multiple RNA or DNA viruses, but many remain narrow in spectrum.

Clinically, antivirals are used for infections such as herpesviruses, HIV, hepatitis B and C, influenza, and respiratory syncytial virus, among others. They vary by route of administration, dosing, and duration, and many require timely initiation. Resistance can develop through viral mutation, reducing efficacy. Safety profiles range from well tolerated to significant hematologic, renal, or hepatic toxicity, and use may be limited in pregnancy or by drug interactions.

Ongoing development seeks more effective agents with wider spectrum, better resistance barriers, and favorable safety profiles, including new polymerase inhibitors, entry inhibitors, and longer-acting formulations.