What is the recommended dosage of Tamiflu (oseltamivir) for treating influenza in adults and children with typical immune systems and no severe underlying medical conditions?

Tamiflu (Oseltamivir) Dosing for Influenza

For adults and adolescents ≥13 years with typical immune systems, the standard treatment dose is 75 mg orally twice daily for 5 days, initiated within 48 hours of symptom onset. 1

Adult and Adolescent Dosing (≥13 years)

Treatment Dosing

• 75 mg twice daily for 5 days (or 12.5 mL of oral suspension twice daily if using liquid formulation) 2, 1
• Must be initiated within 48 hours of symptom onset for maximum effectiveness 2, 1
• Can be taken with or without food, though taking with meals reduces nausea and vomiting 2, 1

Prophylaxis Dosing

• 75 mg once daily for at least 10 days following close contact with an infected individual 2, 1
• Can be extended up to 6 weeks during community outbreaks 1
• Must be initiated within 48 hours of exposure to infected individual 2

Pediatric Dosing (1-12 years)

Weight-Based Treatment (twice daily for 5 days)

• ≤15 kg (≤33 lb): 30 mg twice daily 2, 1
• >15-23 kg (>33-51 lb): 45 mg twice daily 2, 1
• >23-40 kg (>51-88 lb): 60 mg twice daily 2, 1
• >40 kg (>88 lb): 75 mg twice daily 2, 1

Weight-Based Prophylaxis (once daily for 10 days)

• Same weight-based doses as treatment, but administered once daily instead of twice daily 2, 1

Infant Dosing (<12 months)

Treatment Dosing

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

Prophylaxis Dosing

• Infants 3-11 months: 3 mg/kg once daily for 10 days 2
• Prophylaxis not recommended for infants <3 months unless situation is judged critical due to limited safety data 2

Preterm Infant Dosing (based on postmenstrual age)

• <38 weeks postmenstrual age: 1.0 mg/kg twice daily 2, 3
• 38-40 weeks postmenstrual age: 1.5 mg/kg twice daily 2, 3
• >40 weeks postmenstrual age: 3.0 mg/kg twice daily 2, 3

Renal Impairment Adjustments

For patients with creatinine clearance 10-30 mL/min, dose reduction is mandatory to prevent toxicity. 2

Treatment Dosing with Renal Impairment

• 75 mg once daily (instead of twice daily) for 5 days 2, 1

Prophylaxis Dosing with Renal Impairment

• 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 total doses) 2, 1

Special Considerations

• No dose adjustment needed for age alone in elderly patients (≥65 years) with normal renal function 2
• Not recommended for end-stage renal disease patients not on dialysis 1

Formulation Options

Available Forms

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

Oral Suspension Volume Conversions

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

Administration Tips

• Capsules can be opened and mixed with liquid if patient cannot swallow whole 2
• If commercial suspension unavailable, pharmacies can compound suspension based on package insert instructions 2

Critical Timing Considerations

The 48-hour window from symptom onset is crucial—efficacy decreases significantly after this timeframe. 2, 1

• Earlier initiation within the 48-hour window is associated with faster symptom resolution 4
• For prophylaxis, must be started within 48 hours of exposure to infected individual 2, 1
• Do not delay treatment waiting for laboratory confirmation in high-risk patients 2

Common Pitfalls to Avoid

Dosing Errors

• Do not confuse prophylaxis dosing (once daily) with treatment dosing (twice daily)—this is a common prescribing error 5
• Do not use adult doses in children without weight-based adjustment 2
• Do not forget to adjust for renal impairment in elderly patients, as renal function declines with age 6

Timing Errors

• Do not withhold treatment due to mild illness or fever alone 2
• Do not delay initiation waiting for laboratory confirmation in suspected influenza 2

Drug Interactions

• Avoid live attenuated influenza vaccine (LAIV) within 48 hours before oseltamivir use 2
• Do not use oseltamivir for 14 days after LAIV vaccination, as it may interfere with vaccine efficacy 2, 5

Adverse Effects and Tolerability

Common Side Effects

• Nausea and vomiting occur in approximately 5-15% of patients 2, 4
• Gastrointestinal effects are mild, transient, and less likely when taken with food 6, 2, 4
• Other adverse events include headache, diarrhea, and skin reactions 2

Improving Tolerability

• Administration with meals significantly improves gastrointestinal tolerability 2, 3, 1
• Gastrointestinal side effects rarely result in treatment discontinuation 4, 7

Special Populations

Pregnancy

• Oseltamivir can be used during pregnancy with no contraindication 2

Chronic Medical Conditions

• Patients with asthma, chronic pulmonary disease, cardiovascular disease, diabetes, and immunodeficiency can receive oseltamivir 2
• These conditions are not contraindications to treatment 2

Immunocompromised Patients

• Prophylaxis may be continued for up to 12 weeks during community outbreaks 1