Treatment of Influenza B
Oseltamivir 75 mg orally twice daily for 5 days is the recommended first-line treatment for Influenza B in adults and adolescents ≥13 years, initiated within 48 hours of symptom onset. 1
Primary Treatment Recommendation
Oseltamivir is the preferred antiviral agent for Influenza B because it has demonstrated activity against both influenza A and B viruses, unlike amantadine and rimantadine which only work against influenza A. 2, 3 The drug is FDA-approved for treatment of acute, uncomplicated influenza A and B in patients as young as 2 weeks of age who have been symptomatic for no more than 48 hours. 4
Dosing by Age and Weight
Adults and adolescents ≥13 years:
Children ≥12 months (weight-based): 1
- ≤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 9-11 months:
- 3.5 mg/kg per dose twice daily 1
Term infants 0-8 months:
- 3 mg/kg per dose twice daily 1
Preterm infants (dosing by postmenstrual age): 1
- <38 weeks: 1.0 mg/kg per dose twice daily
- 38-40 weeks: 1.5 mg/kg per dose twice daily
40 weeks: 3.0 mg/kg per dose twice daily
Timing and Duration
Treatment must be initiated within 48 hours of symptom onset for maximal benefit, though earlier initiation (within 36 hours) is associated with faster symptom resolution. 1, 2, 5 When started promptly, oseltamivir reduces illness duration by approximately 1-1.5 days and decreases symptom severity by up to 38%. 2, 5
Standard treatment duration is 5 days for uncomplicated influenza. 1 However, longer treatment courses may be necessary for severely ill hospitalized patients, immunocompromised individuals, or those with persistent fever after 6 days. 3
Evidence Supporting Oseltamivir for Influenza B
The most recent high-quality evidence demonstrates that oseltamivir provides significant mortality benefit in hospitalized patients with Influenza B. A 2023 retrospective cohort study of 1,048 hospitalized patients showed that standard-course oseltamivir was associated with an 82% reduction in odds of in-patient death (OR 0.18) compared to no treatment, with no difference in protective effect between Influenza B and Influenza A(H3N2). 6
Experimental human infection studies confirm oseltamivir's antiviral activity against Influenza B, demonstrating significant reductions in viral shedding duration (23.9 hours vs 95.8 hours with placebo) and viral load when used for early treatment. 7
A 2013 prospective intervention study found that Influenza B patients may benefit from higher-dose oseltamivir (150 mg twice daily), showing faster viral RNA decline and clearance compared to standard dosing, though this was a subgroup analysis. 8 However, current guidelines do not recommend routine double-dosing, and standard 75 mg twice daily remains the recommended regimen. 1
Alternative Agents
Zanamivir (inhaled) is an acceptable alternative for patients who cannot tolerate oral oseltamivir or prefer inhalation therapy, provided they do not have underlying respiratory disease. 1, 3
- Adults and children ≥7 years: 10 mg (two 5-mg inhalations) twice daily for 5 days
- FDA-approved for treatment in ages ≥7 years and prophylaxis in ages ≥5 years
Zanamivir is contraindicated in patients with asthma or chronic obstructive pulmonary disease due to risk of serious bronchospasm. 1, 9
Peramivir (IV) is available for patients who cannot absorb oral medications or tolerate inhaled therapy, though it is FDA-approved only for acute uncomplicated influenza in patients ≥2 years who have been symptomatic for no more than 2 days. 1 Its efficacy in severe hospitalized influenza has not been established. 1
Special Populations Requiring Treatment
High-priority groups for antiviral treatment include: 1
- Children <2 years and adults ≥65 years
- Hospitalized patients with confirmed or suspected influenza (regardless of symptom duration) 3
- Patients with severe, progressive, or complicated illness
- Pregnant and postpartum women (within 2 weeks after delivery)
- Immunocompromised individuals
- Patients with chronic medical conditions (pulmonary, cardiovascular, renal, hepatic, hematologic, metabolic, or neurologic disorders)
- Residents of nursing homes and chronic care facilities
- Morbidly obese individuals (BMI ≥40)
Renal Dose Adjustment
For patients with creatinine clearance <30 mL/min: reduce oseltamivir dose by 50% to 75 mg once daily for treatment. 3 Oseltamivir is not recommended for patients with end-stage renal disease not undergoing dialysis. 4
Common Adverse Effects and Management
Nausea and vomiting occur in approximately 10-15% of patients taking oseltamivir. 1, 3 These gastrointestinal effects are typically mild and transient. 5
Taking oseltamivir with food significantly reduces gastrointestinal side effects. 3, 5 Other common adverse events include headache, skin reactions, and diarrhea (particularly in children <1 year). 1
Critical Pitfalls to Avoid
Do not delay treatment while awaiting laboratory confirmation in patients with clinical influenza during community outbreaks, especially in high-risk populations. 1 Molecular assays (RT-PCR) should be used for hospitalized patients when influenza is circulating, as they have superior sensitivity and specificity compared to rapid antigen tests. 1
Do not withhold treatment beyond 48 hours in hospitalized or severely ill patients. While benefit is greatest when initiated early, hospitalized patients with confirmed or suspected influenza should receive oseltamivir regardless of symptom duration. 3
Amantadine and rimantadine are NOT effective against Influenza B and should not be used. 1, 2, 3 These M2 inhibitors only have activity against Influenza A and have high resistance rates among current strains. 3
Prophylaxis Considerations
Oseltamivir is the preferred agent for postexposure chemoprophylaxis for Influenza A and B, but must be initiated within 48 hours of exposure. 1 Prophylaxis dosing is 75 mg once daily for 7 days after last exposure in adults. 1 However, chemoprophylaxis is not a substitute for annual influenza vaccination. 1, 4