Oseltamivir

Neuraminidase inhibitors

ATC code: J05AH02 (Oseltamivir)

Mechanism of action

Prodrug. Converted in the liver to oseltamivir carboxylate, which selectively inhibits influenza A and B neuraminidase. Neuraminidase cleaves sialic acid residues on infected cell surfaces, and without it viral particles cannot bud off. The drug blocks this step and reduces viral spread.

Indications

Influenza

First line

First-line antiviral for influenza in adults and children. RCTs show that starting treatment within 48 hours of symptom onset shortens illness by 1–2 days and reduces complication risk. In hospitalized patients and high-risk groups – pregnant, elderly, immunocompromised – treatment is started even beyond 48 hours.

COVID-19

Not recommended

Not effective against COVID-19. Oseltamivir inhibits neuraminidase, which SARS-CoV-2 lacks. The virus uses spike protein and ACE2 receptor for cell entry – an entirely different mechanism. Early oseltamivir prescriptions during COVID were driven by diagnostic uncertainty when influenza had not been ruled out.

Practical notes

Timing and administration

Take twice daily for 5 days. Taking with food reduces nausea but does not affect bioavailability. Start as early as possible – ideally within 48 hours. In children, the dose is weight-based. For post-exposure prophylaxis – 75 mg once daily for 10 days.

Common myths

Myth: 'oseltamivir doesn't work, Cochrane proved it'. Fact: the 2014 Cochrane review did find limited impact on complications, but the original RCTs were not powered for that endpoint. Meta-analyses of observational data show reduced mortality in hospitalized patients. CDC, IDSA, and WHO still recommend oseltamivir for influenza treatment.

Safety

Contraindications

Hypersensitivity to oseltamivir

Serious adverse effects

Neuropsychiatric events in adolescents – delirium, abnormal behavior, hallucinations (rare, predominantly in Japanese cohorts)
Anaphylaxis and severe skin reactions (Stevens-Johnson syndrome – isolated cases)

Common adverse effects

Nausea
Vomiting
Headache

PregnancyFDA C

FDA category C. However, CDC and ACOG recommend oseltamivir for pregnant women with confirmed or suspected influenza. The benefit from reducing influenza complications during pregnancy outweighs the theoretical risk.