Oseltamivir should be administered to treat critically ill individuals with influenza, particularly when A/H3N2 is circulating, according to a study published in Clinical Infectious Disorders. Oseltamivir is particularly effective against this subtype but does not provide equal efficacy across all strains of influenza.

This study included 1330 participants treated for influenza in hospital intensive care units (ICUs). Participants were all ≥18 years old, were given mechanical ventilation, and were given oseltamivir alone. The primary outcome was mortality in the ICU vs live discharge. Log-binomial models were used to examine the correlation between early oseltamivir use and mortality, and death/discharge subdistribution and cause-specific hazards were estimated using competing risks. In calculating effect estimates, adjustments were made for time between symptom onset and ICU admission, comorbidities, seasonal vaccination for influenza, type of influenza (A/H1N1, A/H3N2, or B), sex, and age group.

Of the 1330 individuals in the ICU for influenza, 46.8% (n=622) died in treatment. Those with influenza subtype A/H3N2 had significantly lower rates of mortality when given early treatment with oseltamivir (relative risk, 0.69; 95% CI, 0.49-0.94), which was attributable to an unchanging cause-specific mortality hazard and a higher cause-specific discharge hazard. Participants given oseltamivir early also had a lower mortality rate than those given oseltamivir late (33.7% vs 48.4%; P =.029), as well as a shorter median length of ICU stay (12 days vs 15 days; P =.003). Individuals who survived had a shorter median ICU length of stay by 1.8 days (95% CI, 0.5-3.5 days). Influenza B and A/H1N1 mortality did not demonstrated an association with early oseltamivir use.

Limitations to this study included a lack of available data on oseltamivir treatment duration and dosage, a lack of analysis on safety outcomes, and an observational study design.

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The study researchers concluded that “in the absence of randomized trials, our study provides strong and important new evidence about oseltamivir use in critically ill influenza patients. It also changes current thinking, by indicating that oseltamivir effectiveness may depend on influenza type,” the researchers concluded. o”[]ur findings support the recommended practice of promptly treating with oseltamivir [in] severely ill patients with suspected influenza, particularly when subtype A/H3N2 is in circulation.”

Reference

Lytras T, Mouratidou E, Andreopoulou A, Bonovas S, Tsiodras S. Effect of early oseltamivir treatment on mortality in critically ill patients with different types of influenza: a multi-season cohort study [published online February 7, 2019]. Clin Infect Dis. doi:10.1093/cid/ciz101