Generic Name

Tamiflu

Mechanism

• Inhibits influenza neuraminidase, the viral surface enzyme required for the release of newly formed virions from infected epithelial cells.
• By blocking neuraminidase, it prevents viral spread within the respiratory tract, reducing viral load and symptom duration.
• Non‑competitive and irreversible binding, allowing effective suppression even at low drug concentrations.

Pharmacokinetics

• Absorption: Oral tablets or liquid are well absorbed; bioavailability ≈ 80 % with a peak plasma level at ~4 h.
• Distribution: Widely distributed; blood‑brain barrier penetration is minimal.
• Metabolism: In the liver, oseltamivir is rapidly dephosphorylated to the active carboxylate metabolite.
• Elimination: Primarily renally excreted; in patients with normal renal function, the half‑life is ~10 h (reflecting total drug, ~13 h for the active metabolite).
• Renal adjustment: Dose reduction in creatinine clearance < 30 mL/min; avoid in severe renal failure.

Indications

• Treatment of uncomplicated influenza A or B in adults, children, and infants older than 7 days within 48 h of symptom onset.
• Post‑exposure prophylaxis for close contacts and at‑risk populations during influenza outbreaks (e.g., hospitalized patients, nursing home residents).

Contraindications

• Allergic reaction to oseltamivir or its excipients (e.g., tartaric acid, polysorbate 80).
• Severe renal impairment (CrCl < 10 mL/min) – contraindicated.
• Pregnancy: Category C; use only if the benefits outweigh potential risks.
• Lactation: Limited data; discuss risk versus benefit.
• Neuropsychiatric events: Rare but reported—especially in adolescents; monitor for mood changes, agitation, or hallucinations.

Dosing

• Adults (≥ 18 y)
• *Treatment*: 75 mg orally twice daily for 5 days.
• *Prophylaxis*: 75 mg orally once daily for 10 days (pre‑exposure) or 75 mg once daily for 5 days (post‑exposure).
• Pediatric (7 days–18 y)
• *Treatment*: 3.0 mg/kg orally twice daily for 5 days.
• *Prophylaxis*: 3.0 mg/kg orally once daily for 10 days (pre‑exposure) or 3.0 mg/kg once daily for 5 days (post‑exposure).
• Infants (7 days–12 m)
• 1.5 mg/kg orally twice daily for 5 days (treatment) or 1.5 mg/kg once daily for 10 days (prophylaxis).
• Liquid formulation (for children) can be given by syringe; tablets can be split into ¼ or ½ doses.
• Take with food to improve absorption and reduce nausea.

Adverse Effects

• Common (≤ 5 %)
• Nausea & vomiting
• Diarrhea
• Headache
• Mild fatigue
• Serious (≤ 1 %)
• Neuropsychiatric events (especially in adolescents) – mood swings, bizarre behavior.
• Severe allergic reactions (anaphylaxis).
• Rare cases of increased mortality in severe influenza infections when delayed treatment.

Monitoring

• Renal function: Serum creatinine and creatinine clearance at baseline, then weekly during therapy if CrCl < 60 mL/min.
• Liver enzymes: ALT, AST prior to initiation and if unexplained hepatitis develops.
• Clinical response: Fever resolution, cough improvement, and overall symptom score.
• Adverse effects: Assess for GI upset and neuropsychiatric changes early in therapy.

Clinical Pearls

• Time is critical: The therapeutic benefit of Tamiflu diminishes sharply after 48 h of symptom onset; never delay initiation.
• Prophylaxis dosing: For outbreak control, a daily 75 mg dose for 10 days is effective; keep contacts for the full period to prevent resurgence.
• Pediatric weight‑based dosing: Use the mg/kg regimens, not tablet count. Liquid formulations are necessary for infants and children with poor tablet swallowing.
• Renal adjustment: Even mild renal impairment (CrCl 30–49 mL/min) warrants a dose reduction to 67 mg BID in adults; verify new dosing every week if kidney function changes.
• Resistance watch: While low in standard use, neuraminidase mutations occur in immunocompromised hosts on prolonged therapy; consider viral resistance testing if the clinical picture worsens.
• Safety in pregnancy: No teratogenic data; routine use is allowed when benefits outweigh theoretical risks.

Tamiflu remains a cornerstone of influenza therapeutics when administered promptly, and these concise data help clinicians and students navigate its optimal use.