Oseltamivir Significantly Reduces Mortality in Hospitalized Patients With Influenza

A large, multicenter study published in JAMA Network Open adds compelling new data to support the use of oseltamivir (Tamiflu; Roche) in adults hospitalized with influenza. Involving 11,073 patients across 30 hospitals in Ontario from 2015 to 2023, the study used a target trial emulation framework to evaluate whether early oseltamivir administration (on hospital day 0 or 1) reduced in hospital mortality compared to supportive care alone. In hospital mortality was 3.5% in the oseltamivir group vs 4.9% in the supportive care group, an adjusted risk difference (aRD) of -1.8%. Time to discharge was also shorter in patients treated with oseltamivir, with an adjusted sub distribution hazard ratio of 1.20, indicating earlier discharge in the antiviral group. Thirty day readmissions were lower in the oseltamivir group compared to the supportive care group, with an aRD of -1.5%. Intensive care unit (ICU) transfers after 48 hours were also less common with oseltamivir treatment.¹

Early Antiviral Intervention

Current US and Canadian recommendations call for antiviral treatment for all patients hospitalized with suspected or confirmed influenza, regardless of symptom duration. However, real world uptake has been inconsistent due to gaps in definitive data.^2-3 This new study provides much needed clarity and reinforces the pharmacist’s role in ensuring early initiation of oseltamivir, preferably within the first hospital day to optimize outcomes. Pharmacists should also proactively identify high risk patients, such as older adults or those with chronic conditions, who are most likely to benefit from prompt antiviral therapy.¹

Oseltamivir is generally well tolerated but can cause adverse effects, most commonly gastrointestinal symptoms such as nausea and vomiting, and less frequently, neuropsychiatric effects.⁴ Pharmacists are uniquely positioned to monitor for these issues, adjust dosing in patients with renal impairment, and evaluate for drug to drug interactions that may arise during hospital stays.

Given that the median age in the study population was 72.6 years old, vigilance is especially warranted in generic patients, who may also have comorbidities requiring complex medication regimens.¹ Pharmacist-driven counseling, medication reconciliation, and discharge planning can help mitigate risks and ensure proper adherence post discharge.

Reducing Readmissions & Optimizing Resource Use

The study’s finding of reduced 30-day readmissions and shorter hospital stays aligns with broader health system goals such as cost containment and quality improvement. By preventing clinical deterioration and minimizing ICU transfers, early antiviral treatment contributes to more efficient use of hospital resources.¹

Pharmacists involved in transitions of care programs should reinforce the importance of adherence to antiviral regimens at discharge and educate patients and caregivers about symptom monitoring and follow up. These efforts may further reduce preventable readmissions and improve patient satisfaction.

Conclusion

This new evidence confirms that oseltamivir initiated within 2 days of admission provides a modest but significant mortality benefit in hospitalized patients with influenza, along with improvements in discharge timing and readmission rates. While randomized controlled trial data are still awaited, this large scale observational study offers strong support for current antiviral treatment guidelines.

Pharmacists remain central to ensuring these recommendations are implemented consistently and safely across health systems.

REFERENCES

1. Bai AD, Al Baluki H, Srivastava S, et al. Oseltamivir treatment and outcomes in adults hospitalized with influenza: a target trial emulation using a multicenter cohort. JAMA Netw Open. 2025;8(6):e2514508. doi:10.1001/jamanetworkopen.2025.14508

2. Uyeki TM, Bernstein HH, Bradley JS, et al. Clinical practice guidelines by the Infectious Diseases Society of America: 2018 update on diagnosis, treatment, chemoprophylaxis, and institutional outbreak management of seasonal influenza. Clin Infect Dis. 2019;68(6):e1-e47. doi: 10.1093/cid/ciy866

3. Public Health Agency of Canada. National Advisory Committee on Immunization (NACI): statement on seasonal influenza vaccine for 2024–2025. Accessed July 11, 2025. https://www.canada.ca/en/public-health/services/publications/vaccines-immunization/national-advisory-committee-immunization-statement-seasonal-influenza-vaccine-2024-2025.html

4. Centers for Disease Control and Prevention. Influenza antiviral medications: summary for clinicians. Updated December 15, 2022. Accessed July 11, 2025. https://www.cdc.gov/flu/hcp/antivirals/summary-clinicians.html?CDC_AAref_Val=https://www.cdc.gov/flu/professionals/antivirals/summary-clinicians.htm