Clinical Experience With Intravenous Zanamivir Under an Emergency Investigational New Drug Program in the United States

TO THE EDITOR—We read the article by Fraaij et al [1] and would like to summarize the available information on intravenous zanamivir from the Food and Drug Administration (FDA)'s Emergency Investigational New Drug (EIND) application process [2]. No intravenous an-tiviral agents for treatment of severe influenza are currently approved in the United States. Since the emergence of 2009 pandemic influenza A virus subtype H1N1 (A[H1N1]pdm09), intravenous zanamivir has been authorized through an EIND application to the FDA as an investigational treatment for patients with serious and life-threatening influenza. As part of the EIND process, treating physicians are encouraged to submit data to the FDA, but reporting of requested data is voluntary. We reviewed the FDA's EIND database on influenza patients who received intravenous zanamivir from April 2009 through April 2011. For the 200 patients identified, we performed a descriptive analysis of reported patient information on age, sex, pregnancy status, baseline comorbidities, virologic test results , antiviral resistance data, other antiviral treatments, clinical complications, supportive care modalities used, intravenous zanamivir treatment duration, adverse events (AEs), and outcomes (Table 1). At the time of intravenous zanamivir request, many patients were critically ill with underlying comorbidities and required intensive care unit admission for severe complications of influenza A virus infection (predominantly due to A[H1N1]pdm09), including respiratory failure and renal failure. Most patients