What is the recommended dose of Tamiflu (Oseltamivir) for patients with normal renal function and impaired renal function, across different age groups and weights?

Tamiflu (Oseltamivir) Dosing Guidelines

Standard Adult Dosing (≥13 years, Normal Renal Function)

For treatment of influenza, adults and adolescents ≥13 years should receive 75 mg twice daily for 5 days, initiated within 48 hours of symptom onset. 1, 2

• For prophylaxis following exposure: 75 mg once daily for 10 days (must start within 48 hours of contact) 1, 2
• During community outbreak: 75 mg once daily for up to 6 weeks 2
• Take with food to reduce nausea and vomiting, which occur in approximately 10% of patients but are typically mild and transient 3, 4

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Pediatric Dosing (≥1 year, Normal Renal Function)

Weight-based dosing is essential for children 1-12 years: 1, 3, 2

Treatment (twice daily for 5 days):

• ≤15 kg (≤33 lb): 30 mg twice daily 1, 3
• >15-23 kg (>33-51 lb): 45 mg twice daily 1, 3
• >23-40 kg (>51-88 lb): 60 mg twice daily 1, 3
• >40 kg (>88 lb): 75 mg twice daily 1, 3

Prophylaxis (once daily for 10 days):

• Same weight-based doses as treatment, but given once daily instead of twice daily 3, 5

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Infant Dosing (<1 year, Normal Renal Function)

Term Infants (≥37 weeks gestation at birth):

• 9-11 months: 3.5 mg/kg per dose twice daily for 5 days 1, 3
• 0-8 months: 3.0 mg/kg per dose twice daily for 5 days 1, 3
• Prophylaxis (3-11 months): 3.0 mg/kg once daily for 10 days 3, 5
• Prophylaxis NOT recommended for infants <3 months unless situation is critical due to limited safety data 3, 5

Preterm Infants (Critical Distinction):

Never use term infant dosing for preterm infants—they require substantially lower doses based on postmenstrual age (gestational age + chronological age) due to immature renal function: 1, 3, 5

• <38 weeks postmenstrual age: 1.0 mg/kg twice daily 1, 3
• 38-40 weeks postmenstrual age: 1.5 mg/kg twice daily 1, 3
• >40 weeks postmenstrual age: 3.0 mg/kg twice daily 1, 3
• For extremely preterm infants (<28 weeks), consult pediatric infectious diseases 1

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Renal Impairment Dosing Adjustments

Dose reductions are mandatory when creatinine clearance falls below 60 mL/min—age is less important than renal function in older adults: 3, 2

Adults with Renal Impairment:

CrCl >30-60 mL/min: 2

• Treatment: 30 mg twice daily for 5 days
• Prophylaxis: 30 mg once daily

CrCl 10-30 mL/min: 1, 3, 2

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

End-Stage Renal Disease (ESRD) on hemodialysis: 2

• Treatment: 30 mg immediately, then 30 mg after every hemodialysis cycle (not to exceed 5 days)
• Prophylaxis: 30 mg immediately, then 30 mg after alternate hemodialysis cycles

ESRD on CAPD: 2

• Treatment: Single 30 mg dose immediately
• Prophylaxis: 30 mg immediately, then 30 mg once weekly

Pediatric Patients with Renal Impairment (CrCl 10-30 mL/min):

Reduce the child's weight-based dose to once daily (instead of twice daily) for treatment. 5 For prophylaxis, give half the standard once-daily dose daily, or the full once-daily dose every other day for 10 days. 5

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Formulations and Administration

Oseltamivir is available as: 1, 3

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

Suspension Volume Conversions:

• 30 mg dose = 5 mL 3
• 45 mg dose = 7.5 mL 3
• 60 mg dose = 10 mL 3
• 75 mg dose = 12.5 mL 3

If commercial suspension unavailable, pharmacies can compound suspension per package insert instructions (final concentration 6 mg/mL). 1, 3

Capsules can be opened and contents mixed with liquid for patients unable to swallow whole capsules. 3

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Critical Clinical Pearls

Timing is Everything:

• Treatment must be initiated within 48 hours of symptom onset for maximum effectiveness 3, 6
• Prophylaxis must be started within 48 hours of exposure 6
• Do not wait for laboratory confirmation in patients with influenza-like illness during local influenza activity—start empiric treatment immediately 6

Drug Interaction Warning:

• Avoid live attenuated influenza vaccine (LAIV) within 48 hours before oseltamivir use 3, 6
• Do not use oseltamivir for 14 days after LAIV vaccination as it may interfere with vaccine efficacy 3, 6

Common Pitfalls to Avoid:

• Never use weight-based dosing for children ≥1 year (30,45,60,75 mg unit doses) in infants <1 year—these doses are too high 5
• Never confuse term and preterm infant dosing—preterm infants require dramatically lower doses 3, 5
• Do not confuse GFR with creatinine clearance when calculating renal dosing 5
• In older adults, focus on renal function, not age—standard 75 mg twice daily is appropriate if CrCl >60 mL/min 3

Tolerability:

• Nausea occurs in ~10% and vomiting in ~9% of adults (vs 6% and 3% with placebo) 3
• In children, vomiting occurs in 14.3% (vs 8.5% with placebo) 3
• Only ~1% discontinue due to GI side effects 3
• Taking with food significantly reduces severity of nausea and vomiting 3, 4