Is Oseltamivir (Tamiflu) effective against Influenza B?

From the Guidelines

Yes, Tamiflu (oseltamivir) is effective against influenza B, as it can reduce the duration of uncomplicated influenza A and B illness by approximately 1 day compared with placebo when administered within 2 days of illness onset 1. The mechanism of action of Tamiflu involves inhibiting the neuraminidase enzyme found on the surface of both influenza A and B viruses, preventing them from spreading within the body. Key points to consider when using Tamiflu for influenza B treatment include:

• The standard adult dosage for treatment is 75 mg twice daily for 5 days, starting within 48 hours of symptom onset for maximum effectiveness.
• For children, the dose is weight-based.
• Tamiflu can reduce the duration of flu symptoms by about 1-2 days and may decrease the risk of complications when started promptly.
• It can also be used preventively after exposure to the flu.
• Common side effects include nausea and vomiting, which can be reduced by taking the medication with food. While the evidence from various studies, including those from 2002 1, 2004 1, 2006 1, and 2007 1, supports the effectiveness of Tamiflu against influenza B, it's essential to note that more clinical data are available concerning the efficacy of zanamivir and oseltamivir for treatment of influenza A virus infection than for treatment of influenza B virus infection. However, data from human clinical studies have indicated that zanamivir and oseltamivir have activity against influenza B viruses 1. Observational studies have also determined that oseltamivir reduces severe clinical outcomes in patients hospitalized with influenza, including a significant reduction in mortality among patients who received oseltamivir treatment 1. In the context of real-life clinical medicine, prioritizing the reduction of morbidity, mortality, and improvement of quality of life, the use of Tamiflu for the treatment of influenza B is supported by the available evidence 1.

From the FDA Drug Label

Oseltamivir phosphate for oral suspension is indicated for the treatment of acute, uncomplicated illness due to influenza A and B infection in patients 2 weeks of age and older who have been symptomatic for no more than 48 hours. Oseltamivir phosphate for oral suspension is indicated for the prophylaxis of influenza A and B in patients 1 year and older.

Tamiflu (oseltamivir) is effective against flu B. The drug label directly states that oseltamivir phosphate for oral suspension is indicated for the treatment and prophylaxis of influenza B infection. 2

• Key points:
  • Indicated for treatment of influenza B in patients 2 weeks of age and older
  • Indicated for prophylaxis of influenza B in patients 1 year and older
  • Should be initiated within 48 hours of symptom onset for treatment or close contact with an infected individual for post-exposure prophylaxis

From the Research

Effectiveness of Tamiflu against Flu B

• Tamiflu (oseltamivir) is a prodrug of oseltamivir carboxylate, a potent and selective inhibitor of the neuraminidase glycoprotein essential for replication of influenza A and B viruses 3.
• Studies have shown that oseltamivir reduces the duration of the disease by up to 1.5 days and the severity of illness by up to 38% compared with placebo when initiated within 36 hours of symptom onset 3.
• Oseltamivir has demonstrated efficacy when used for seasonal or household prophylaxis, preventing the development of naturally acquired influenza by >70% compared with placebo in unvaccinated otherwise healthy adults 3.
• The drug has also shown efficacy in the treatment of children with influenza, and data suggest that it may be of use in high-risk populations such as the elderly or those with chronic cardiac or respiratory disease 3, 4.
• However, a study found that the duration of fever after administration of oseltamivir was shorter in patients with influenza A infection than in patients with influenza B infection, suggesting that oseltamivir may be more effective against influenza A 5.

Safety and Tolerability

• Oseltamivir is generally well tolerated, with nausea and vomiting being the most commonly reported events 3, 6.
• Gastrointestinal events are usually mild and transient, and can be reduced by taking oseltamivir with food 3.
• The safety profile of oseltamivir has been extensively reviewed, and it has been found to be safe for use in standard and special patient populations, including children and the elderly 6, 7.

Clinical Experience and Recommendations

• Oseltamivir has been recommended by the World Health Organization (WHO) for use in the clinical management of pandemic and seasonal influenza of varying severity 6.
• The WHO also recommends oseltamivir as the primary antiviral agent for treatment of avian H5N1 influenza infection in humans 6.
• Oseltamivir is effective in reducing symptom burden in those with influenza A or B infection, and is preventative against developing infection after exposure 7.