Oseltamivir

• Treatment of Influenza A and B:
  For acute, uncomplicated influenza infection in patients aged 2 weeks and older, when started within 48 hours of symptom onset.
• Prevention of Influenza:
  For prophylaxis against influenza A and B in individuals aged 1 year and older after exposure to confirmed or suspected cases.
• Severe Influenza (Off-label):
  Used in hospitalized patients with complicated or severe influenza infections under clinical discretion.
• Other Clinical Uses (Off-label):
  Management of avian influenza and novel influenza strains pending susceptibility data.

• Route: Oral (capsule, suspension).
• Adults and Adolescents (≥13 years):
• Treatment: 75 mg twice daily for 5 days.
• Prophylaxis: 75 mg once daily for at least 10 days post-exposure.
• Pediatrics (1 year to 12 years):
  Dose is weight-based; typically ranges from 30 mg to 75 mg twice daily for treatment, once daily for prophylaxis, duration same as adults.
• Infants (2 weeks to <1 year):
  Dose per pediatric guidelines; oral suspension preferred.
• Elderly:
  No adjustment required solely based on age.
• Renal Impairment:
  Dose adjustment recommended for creatinine clearance ≤60 mL/min; for example, 30 mg once daily for prophylaxis, 30 mg twice daily for treatment, with further adjustments for severe impairment.
• Hepatic Impairment:
  No dose adjustment necessary.
• Duration:
  Treatment courses usually 5 days; prophylaxis extends to 10 days or longer during outbreaks.

Oseltamivir is a prodrug rapidly converted by hepatic esterases into its active metabolite, oseltamivir carboxylate. This metabolite selectively inhibits the neuraminidase enzyme on the surface of influenza viruses. Neuraminidase inhibition prevents the cleavage of sialic acid residues on host cells, thereby blocking viral release and spread from infected cells. This results in reduced viral replication and mitigated severity and duration of influenza symptoms.

• Absorption: Rapid and efficient oral absorption; peak plasma levels reached within 2–3 hours.
• Bioavailability: Approximately 80%.
• Distribution: Volume of distribution ~23–26 liters; widely distributed.
• Metabolism: Extensive hepatic conversion to active metabolite; minimal CYP450 involvement.
• Half-life: 6–10 hours for active metabolite.
• Excretion: Primarily renal elimination (>99%) of unchanged active metabolite.

• Pregnancy: FDA Category C — Animal studies reveal no clear risk; human data limited. Use only if potential benefits justify potential risks.
• Lactation: Excreted in breast milk at low concentrations; breastfeeding is generally considered safe but caution is advised.

• Antiviral agent, neuraminidase inhibitor.

• Hypersensitivity to oseltamivir or any component of the formulation.
• History of severe allergic reactions to neuraminidase inhibitors.

• Monitor for neuropsychiatric events, including delirium and abnormal behavior, especially in children and adolescents.
• Use cautiously in patients with renal impairment; dose adjustment necessary.
• Not a substitute for annual influenza vaccination.
• Initiate treatment as early as possible, ideally within 48 hours of symptom onset.
• Be alert for signs of allergic reactions.

• Common: Nausea, vomiting, abdominal pain, headache, fatigue.
• Uncommon/Serious: Neuropsychiatric events (delirium, hallucinations), hypersensitivity reactions (rash, anaphylaxis), Stevens-Johnson syndrome (rare).
• Timing: Gastrointestinal side effects generally occur early and are mild to moderate; neuropsychiatric events often reported during treatment course.

• Minimal drug interaction potential due to limited CYP450 involvement.
• Caution with probenecid, which may increase oseltamivir plasma concentration.
• Avoid concomitant use with live attenuated influenza vaccine within 2 weeks.
• No significant interaction with common medications documented.

• Continued endorsement by CDC and WHO as first-line treatment and prophylaxis for influenza.
• Updated safety warnings regarding neuropsychiatric effects, particularly in pediatric patients.
• Emphasis on early initiation of therapy to maximize efficacy.
• No major changes in dosing or indications recently.

• Store at 20°C to 25°C (68°F to 77°F).
• Protect from moisture and light.
• Capsules should remain in tightly closed containers.
• Do not freeze oral suspension; refrigerate if prescribed, and discard after recommended period.