What is the recommended dose of the medication?

Oseltamivir (Tamiflu) Dosing Recommendations

Standard Adult and Adolescent Dosing (≥13 years)

For treatment of influenza, the recommended dose is 75 mg orally twice daily for 5 days, and for prophylaxis, 75 mg once daily for 10 days. 1, 2

• Treatment should be initiated within 48 hours of symptom onset for maximum effectiveness 1, 2
• Administration with meals may improve gastrointestinal tolerability, as nausea and vomiting occur in approximately 10-15% of patients 1, 2
• The 5-day treatment course shortens illness duration by approximately 24-36 hours compared to placebo 2

Pediatric Weight-Based Dosing (≥12 months)

Children require weight-based dosing administered twice daily for treatment (5 days) or once daily for prophylaxis (10 days): 1, 2

• ≤15 kg (≤33 lb): 30 mg per dose
• >15-23 kg (>33-51 lb): 45 mg per dose
• >23-40 kg (>51-88 lb): 60 mg per dose
• >40 kg (>88 lb): 75 mg per dose

Infant Dosing (<12 months)

Term infants require age-based mg/kg dosing, not the categorical weight bands used for older children: 1, 2

• Term infants 9-11 months: 3.5 mg/kg per dose twice daily for treatment 1, 2
• Term infants 0-8 months: 3.0 mg/kg per dose twice daily for treatment 1, 2
• Prophylaxis (3-11 months): 3.0 mg/kg once daily for 10 days 2
• Prophylaxis is NOT recommended for infants <3 months unless the situation is judged critical due to limited safety data 1, 2

Critical Pitfall: Preterm Infant Dosing

Preterm infants require substantially lower doses based on postmenstrual age (PMA = gestational age + chronological age), NOT weight alone, because immature renal function leads to toxic drug accumulation: 1, 2

• <38 weeks PMA: 1.0 mg/kg twice daily
• 38-40 weeks PMA: 1.5 mg/kg twice daily
• >40 weeks PMA: 3.0 mg/kg twice daily
• For extremely preterm infants (<28 weeks), consult a pediatric infectious disease specialist before initiating therapy 1, 2

Renal Impairment Dose Adjustments

Dose reduction is mandatory when creatinine clearance falls below 60 mL/min, as oseltamivir carboxylate concentrations increase proportionally with declining renal function: 1, 2

For Creatinine Clearance 10-30 mL/min:

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

For Creatinine Clearance <10 mL/min:

• Limited data available; hemodialysis contributes minimally to drug clearance 1
• Oseltamivir is not recommended for end-stage renal disease patients not on dialysis 2

Elderly Patients (≥65 years)

Age alone does not require dose reduction—renal function is the determining factor: 2

• Standard dose (75 mg twice daily for treatment, 75 mg once daily for prophylaxis) remains appropriate with normal renal function 2
• Assess creatinine clearance in all elderly patients, as renal function declines with age 1
• Apply renal impairment dose adjustments when CrCl <60 mL/min 2

Formulation and Administration

Oseltamivir is available as capsules (30 mg, 45 mg, 75 mg) and oral suspension (6 mg/mL when reconstituted): 1, 2

Oral Suspension Volumes (6 mg/mL concentration):

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

Critical Administration Points:

• Use a calibrated 3-5 mL oral syringe for infants—the syringe supplied with commercial product is unsuitable for small volumes 2
• If commercial suspension is unavailable, pharmacies can compound a 6 mg/mL suspension per package insert instructions 1, 2
• Capsules can be opened and contents mixed with liquid for patients unable to swallow whole 2
• Never use household spoons for measurement 2

Treatment Duration and Completion

The full 5-day treatment course must be completed even if symptoms improve earlier: 2

• Completing the full course ensures adequate viral suppression and helps prevent resistance 2
• Do not stop therapy 24-48 hours after symptom resolution—that recommendation applied only to older drugs (amantadine/rimantadine), not neuraminidase inhibitors 2

Drug Interactions and Contraindications

Avoid live attenuated influenza vaccine (LAIV) within 48 hours before oseltamivir use, and do not use oseltamivir for 14 days after LAIV vaccination: 2

• No absolute contraindications exist for oseltamivir use in pregnancy, chronic medical conditions (asthma, cardiovascular disease, diabetes, immunodeficiency), or mild febrile illness 2
• Oseltamivir is FDA-approved for children as young as 2 weeks of age 1, 2

Common Adverse Effects

Gastrointestinal effects (nausea, vomiting, diarrhea) occur in 10-15% of patients but are generally mild, transient, and manageable: 2

• Taking oseltamivir with food significantly reduces nausea and vomiting severity 2
• Only approximately 1% of patients discontinue therapy due to gastrointestinal side effects 2
• In pediatric trials, 14.3% experienced vomiting compared to 8.5% with placebo 2