What is the dosage and use of Oseltamivir for influenza?

Oseltamivir Dosage and Use for Influenza

Oseltamivir is dosed at 75 mg orally twice daily for 5 days for treatment of influenza in adults and adolescents ≥13 years, and 75 mg once daily for 10 days for prophylaxis, with treatment ideally initiated within 48 hours of symptom onset for maximum benefit. 1, 2, 3

Treatment Dosing

Adults and Adolescents (≥13 years)

• 75 mg orally twice daily for 5 days is the standard treatment dose 1, 2, 3
• Treatment should be initiated within 48 hours of symptom onset for optimal efficacy, reducing illness duration by approximately 1-1.5 days 2, 4, 5
• Do not withhold treatment in hospitalized or high-risk patients even if presenting beyond 48 hours, as mortality benefit persists with later initiation 2
• Treatment within 12 hours of symptom onset provides an additional 74.6 hours of benefit compared to treatment at 48 hours 5

Pediatric Patients (≥12 months to 12 years)

Weight-based dosing twice daily for 5 days: 1, 2, 3

• ≤15 kg: 30 mg twice daily

• 15-23 kg: 45 mg twice daily

• 23-40 kg: 60 mg twice daily

• 40 kg: 75 mg twice daily

Infants (<12 months)

• 9-11 months: 3.5 mg/kg per dose twice daily for 5 days 2, 6, 3
• Term infants 0-8 months: 3 mg/kg per dose twice daily for 5 days 1, 2, 6, 3
• Infants <3 months: 3 mg/kg per dose twice daily for 5 days 1

Preterm Infants (Postmenstrual Age-Based Dosing)

Dosing based on gestational age + chronological age, twice daily for 5 days: 1, 2, 6

• <38 weeks postmenstrual age: 1.0 mg/kg twice daily
• 38-40 weeks postmenstrual age: 1.5 mg/kg twice daily

• 40 weeks postmenstrual age: 3.0 mg/kg twice daily

Prophylaxis Dosing

Adults and Adolescents (≥13 years)

• 75 mg orally once daily for post-exposure prophylaxis (10 days) or seasonal prophylaxis (up to 6 weeks) 1, 2, 7, 3
• Initiate within 48 hours following close contact with an infected individual 2, 7, 3
• In immunocompromised patients, prophylaxis may be continued for up to 12 weeks 3

Pediatric Patients (≥1 year to 12 years)

Same weight-based doses as treatment, but once daily instead of twice daily for 10 days: 1, 2, 7, 3

• ≤15 kg: 30 mg once daily

• 15-23 kg: 45 mg once daily

• 23-40 kg: 60 mg once daily

• 40 kg: 75 mg once daily

Infants (3-11 months)

• 3 mg/kg once daily for 10 days 1, 2, 7
• Prophylaxis is NOT recommended for infants <3 months unless the situation is judged critical due to limited safety data 1, 2, 7

Renal Impairment Adjustments

Creatinine Clearance 10-30 mL/min

• Treatment: 75 mg once daily (instead of twice daily) for 5 days 1, 2, 6
• Prophylaxis: Either 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 total doses) 1, 2, 6, 7

End-Stage Renal Disease

• Oseltamivir is NOT recommended for patients with end-stage renal disease not undergoing dialysis 3

Formulation and Administration

Available Forms

• Capsules: 30 mg, 45 mg, 75 mg 1, 2, 6, 3
• Oral suspension: 6 mg/mL when reconstituted 1, 2, 6, 3

Suspension Dosing Volumes

• 30 mg dose = 5 mL 2, 6
• 45 mg dose = 7.5 mL 2, 6
• 60 mg dose = 10 mL 2, 6
• 75 mg dose = 12.5 mL 1, 2, 6

Administration Tips

• May be taken with or without food, but taking with food improves gastrointestinal tolerability and reduces nausea 2, 3, 4, 5
• Capsules can be opened and contents mixed with liquid if patient cannot swallow capsules whole 2
• If commercial suspension unavailable, pharmacies can compound suspension from capsules to achieve 6 mg/mL concentration 2

Special Populations

Pregnancy

• Same dosing as non-pregnant adults: 75 mg twice daily for 5 days 2
• Pregnancy substantially increases risk of severe influenza complications, and benefit-risk profile strongly favors treatment 2
• Oseltamivir is preferred over zanamivir in pregnancy 2
• Breastfeeding is not a contraindication to oseltamivir use 2

Immunocompromised Patients

• Treatment should be given regardless of time since symptom onset 2
• May require extended treatment duration beyond 5 days if illness is prolonged 1
• Prophylaxis may be continued for up to 12 weeks during community outbreaks 3

Drug Interactions and Contraindications

Live Attenuated Influenza Vaccine (LAIV)

• Avoid oseltamivir within 48 hours before LAIV vaccination 2, 6
• Do not use oseltamivir for 14 days after LAIV vaccination, as it may interfere with vaccine efficacy 2, 6, 7

Underlying Conditions

• Asthma, chronic pulmonary disease, cardiovascular disease, diabetes, and immunodeficiency are NOT contraindications to oseltamivir use 2
• Oseltamivir is approved for use in children as young as 2 weeks of age 1, 2

Adverse Effects

Common Side Effects

• Nausea and vomiting are the most common adverse events, occurring in approximately 10-15% of patients 2, 4, 5, 8
• Gastrointestinal effects are typically mild and transient, resolving within 1-2 days 2, 5
• Headache and other minor symptoms may occur 2

Minimizing Side Effects

• Taking oseltamivir with food significantly reduces nausea and vomiting 2, 3, 4, 5

Clinical Efficacy

Treatment Benefits

• Reduces illness duration by 1-1.5 days when initiated within 48 hours 2, 4
• Decreases severity of illness by up to 38% 4
• Reduces incidence of secondary complications including otitis media, bronchitis, pneumonia, and sinusitis 4, 5
• Significantly reduces mortality in hospitalized and high-risk patients even when initiated beyond 48 hours 2

Prophylaxis Benefits

• Provides >70% protective efficacy for seasonal prophylaxis in unvaccinated adults 4, 8
• Demonstrates 92% protective efficacy when used adjunctively in previously vaccinated high-risk elderly patients 4
• Reduces household transmission risk when initiated within 48 hours of index case symptom onset 4

Common Prescribing Pitfalls

Critical Errors to Avoid

• Do not confuse prophylaxis dosing (once daily) with treatment dosing (twice daily) - this is a frequent prescribing error 7
• Do not delay treatment while waiting for laboratory confirmation in high-risk patients, as rapid antigen tests have poor sensitivity 2
• Do not withhold treatment based on mild illness or fever alone 2
• Do not use oseltamivir if LAIV was administered within the past 2 weeks 7

Resistance Considerations

• Currently circulating influenza A (H3N2) and 2009 H1N1 viruses are resistant to adamantanes (amantadine, rimantadine), making neuraminidase inhibitors like oseltamivir the preferred agents 1
• Sporadic oseltamivir-resistant strains have been identified but remain rare with limited public health impact 1
• Resistant mutants demonstrate reduced transmissibility and pathogenicity 5