Incidence of NAION not increased by PDE-5 inhibitor, data show

May 22, 2006

Results of an analysis based on approximately 52,000 patient-yearsof observation demonstrate that the incidence of nonarteriticanterior ischemic optic neuropathy (NAION) among men receivingsildenafil citrate (Viagra) is no higher than that occurring amongmen in the general population, Rachel E. Sobel, MPH, of Pfizer,reported yesterday.

Results of an analysis based on approximately 52,000 patient-years of observation demonstrate that the incidence of nonarteritic anterior ischemic optic neuropathy (NAION) among men receiving sildenafil citrate (Viagra) is no higher than that occurring among men in the general population, Rachel E. Sobel, MPH, of Pfizer, reported yesterday.

The analysis reviewed data from 103 company-sponsored open-label and double-blind sildenafil global clinical trials including more than 13,400 men and two European observational studies - the prospective International Men's Health Study of more than 3,800 men and the Prescription Event Monitoring (PEM) study of more than 28,000 men that was conducted independently by the Drug Safety Research Unit at the University of Southampton. Only a single case of NAION was identified in the PEM, and that translated into an unadjusted incidence rate of 2.8 cases per 100,000 patient-years.

Data from two published papers investigating spontaneous NAION in the general U.S. population were used for comparison. In those two papers, the reported incidences of NAION among men age 50 years and older were 2.5 cases per 100,000 men and 11.8 per 100,000 men, respectively.

"While there have been rare, spontaneous reports of NAION occurring in conjunction with the use of sildenafil or other oral PDE-5 inhibitors, there has not been good evidence to support any cause-and-effect relationship in those cases," said Sobel, Pfizer's associate director, global epidemiology/safety and risk management.