Risk of fatal adverse events after H1N1 influenza vaccination.

Figure 1. Number of fatal cases. Most of the fatal cases, which peaked in number within 24 h after H1N1 influenza vaccination, occurred within 4 days after vaccination. EFV levels ( ) and NVP dosage P p .008 ( ) were independently and posiP ! .001 tively associated with the steady-state plasma NVP levels in multivariate analysis. The switch from EFV to NVP can lead to a time-limited subtherapeutic steadystate plasma NVP level. In this context, genetic variability may be responsible for the low steady-state plasma NVP levels among patients with previous low steadystate plasma EFV levels. Although the virologic consequences of a time-limited subtherapeutic steady-state plasma NVP level are unknown, subtherapeutic steadystate plasma NVP levels have been associated with virologic failure after a switch from protease inhibitor–based therapy [6]. To limit exposure to subtherapeutic steady-state plasma NVP levels, we suggest that determining the steady-state plasma EFV level before the switch to NVP may be helpful for deciding whether to start NVP at 200 mg per day (patients with high baseline EFV levels) or 400 mg per day (patients with low baseline EFV levels).