oseltamivir
Brand: Tamiflu
Prototype Drug
Drug Class: antiviral
Drug Family: antiviral
Subclass: neuraminidase inhibitor
Organ Systems: infectious-disease
Mechanism of Action
Prodrug converted by hepatic esterases to oseltamivir carboxylate, which competitively inhibits influenza A and B neuraminidase; neuraminidase is required for viral budding and release from infected cells, limiting viral spread.
influenza neuraminidase
Indications
- influenza A and B treatment (within 48 hours of symptom onset)
- influenza prophylaxis (post-exposure and seasonal)
- treatment of serious influenza in hospitalized patients (regardless of symptom duration)
- H5N1 avian influenza (treatment and prophylaxis)
Contraindications
- known hypersensitivity to oseltamivir
Adverse Effects
Common
- nausea
- vomiting (take with food to minimize)
- headache
- diarrhea
Serious
- neuropsychiatric events (confusion, hallucinations, self-injury — reported mainly in pediatric patients in Japan; causality uncertain)
- bronchospasm (rare)
- serious skin reactions
Pharmacokinetics (ADME)
| Absorption | ~75% oral bioavailability as oseltamivir carboxylate; food does not affect bioavailability |
| Distribution | Oseltamivir carboxylate: protein binding 3%; widely distributed |
| Metabolism | Prodrug hydrolyzed by hepatic esterases (primarily CES1) to active carboxylate |
| Excretion | Renal; dose adjustment for CrCl <30 mL/min |
| Half-life | 6–10 hours (carboxylate) |
| Onset | 1–2 hours |
| Peak | 3–4 hours |
| Duration | 12 hours (q12h dosing x5 days for treatment) |
| Protein Binding | 3% |
| Vd | ~23 L |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| probenecid | reduces renal tubular secretion of oseltamivir carboxylate; doubles levels | minor |
| influenza live attenuated vaccine (LAIV) | oseltamivir may reduce LAIV efficacy — separate by 48 hours before and 2 weeks after LAIV | moderate |
Nursing Considerations
- Administer within 48 hours of symptom onset for maximum benefit; treatment beyond 48 hours may still be beneficial in severe illness, hospitalized patients, or immunocompromised hosts
- Take with food to reduce GI side effects; suspension can be prepared from capsules if needed for patients who cannot swallow capsules
- Renal dose adjustment: for CrCl 10–30 mL/min, reduce to 75 mg once daily (treatment) or 30 mg once daily (prophylaxis); for CrCl <10 or ESRD on dialysis, specific dosing protocols apply
- For post-exposure prophylaxis: 75 mg once daily x10 days; for seasonal prophylaxis: 75 mg once daily for up to 6 weeks during outbreak period
Clinical Pearls
- Oseltamivir reduces duration of influenza by approximately 1 day and reduces risk of complications (pneumonia, hospitalization) — benefits are most pronounced in high-risk patients (elderly, immunocompromised, pregnant) even when started late
- Oseltamivir resistance in influenza A (H275Y mutation in neuraminidase) has been documented in seasonal H1N1 strains and in immunocompromised patients on prolonged therapy — peramivir IV or inhaled zanamivir may be alternatives
Safety Profile
Pregnancy use-with-caution
Lactation use-with-caution
Renal Adjustment Required
Hepatic Adjustment Not required
TDM Not required
Concordance Terms
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