Evaluation of the antiviral response to zanamivir administered intravenously for treatment of critically ill patients with pandemic influenza A (H1N1) infection

Abstract

A retrospective nationwide study on the use of intravenous (IV) zanamivir in patients receiving intensive care who were pretreated with oseltamivir in the Netherlands was performed. In 6 of 13 patients with a sustained reduction of the viral load, the median time to start IV zanamivir was 9 days (range, 4-11 days) compared with 14 days (range, 6-21 days) in 7 patients without viral load reduction (P = .052). Viral load response did not influence mortality. We conclude that IV zanamivir as late add-on therapy has limited effectiveness. The effect of an immediate start with IV zanamivir monotherapy or in combination with other drugs need to be evaluated.

Figure 1.

Virological response to intravenous (IV) zanamivir in 13 patients. A, Change in baseline viral load detected in the upper respiratory tract (URT); B, change in baseline viral load detected in the lower respiratory tract (LRT). Eight patients were treated for >10 days, and 5 patients were treated for <10 days. Of those 5 patients, 2 died and 3 clinically recovered, and zanamivir IV medication was stopped (patients 7, 9, and 13). Because patient 12 had undetectable viral loads in the URT sample, these data are not included in the figure for change in baseline URT viral load. Each line represents a single patient. Data obtained from patients with a sustained viral load reduction are depicted in green, and data for those without a viral response are depicted in red; the black dashed line represents the delta viral load of −1 log₁₀ virus particles (vp) per milliliter.