Oseltamivir phosphate is a prodrug of oseltamivir carboxylate, a potent and selective inhibitor of influenza virus neuraminidase (sialidase). It is an antiviral medication used for the treatment and prophylaxis of influenza A and B virus infections. In the Indian context, it is a critical drug for managing seasonal influenza outbreaks and is included in national guidelines for pandemic preparedness.
Adult: Treatment: 75 mg orally twice daily for 5 days. Prophylaxis: 75 mg orally once daily for at least 10 days (up to 6 weeks during community outbreak).
Note: Can be taken with or without food. Taking with food may minimize gastrointestinal upset. Capsule should be swallowed whole with water. For patients unable to swallow capsules, an oral suspension can be prepared from the capsule contents or a commercially available powder for suspension can be used.
Oseltamivir phosphate is an orally administered ethyl ester prodrug. It is hydrolyzed in the liver to the active metabolite, oseltamivir carboxylate. This active form is a competitive inhibitor of influenza virus neuraminidase, an enzyme essential for viral replication. Neuraminidase cleaves sialic acid residues on the surface of infected cells and the viral envelope, facilitating the release of progeny virions and their spread within the respiratory tract.
Pregnancy: Category C: Animal studies showed fetal toxicity at high doses. Use during pregnancy only if the potential benefit justifies the potential risk to the fetus. Recommended for treatment of pregnant women with suspected or confirmed influenza due to higher risk of severe illness.
Driving: May cause dizziness, headache, or fatigue. Patients should be cautioned about driving or operating machinery if affected.
| Probenecid | Inhibits renal tubular secretion of oseltamivir carboxylate, doubling its plasma AUC. Not recommended for co-administration. | Moderate |
| Live Attenuated Influenza Vaccine (LAIV) | Oseltamivir may inhibit viral replication of the vaccine virus, potentially reducing efficacy. LAIV should be deferred until >48 hours after last oseltamivir dose, or oseltamivir should be deferred for >2 weeks after LAIV administration. | Moderate |
| Clopidogrel | Theoretical competition for esterase activation, but no clinically significant interaction established. | Minor |