Co-prescription of sildenafil with nitrates still occurs

May 24, 2005

A study estimating the dispensation rate of interacting medications to an outpatient population found that while only 0.05% of patients received co-prescriptions for medications that could potentially cause adverse effects, about half of these were given were for sildenafil citrate (Viagra) and one of two different nitrates.

A study estimating the dispensation rate of interacting medications to an outpatient population found that while only 0.05% of patients received co-prescriptions for medications that could potentially cause adverse effects, about half of these were given were for sildenafil citrate (Viagra) and one of two different nitrates.

"I think that was a particularly unexpected finding of the study," said Charles D. Scales, MD, research associate at Duke University, who presented the study yesterday.

Data for the 1999 study was obtained from one of the largest pharmaceutical benefit management companies in the United States with beneficiaries in all 50 states, representing approximately 1,200 insurance companies.

All prescription claims were examined, and a subset of more than 800,000 patients had at least two claims. Of those, 376 patients had two prescriptions filled for drugs that should never be prescribed together (class 1 Interactions).

In this group of 376 patients, 263 patients (65.9%) filed claims for sildenafil and a nitrate medication, with 199 prescriptions (30.2%) for sildenafil and nitroglycerin, and 127 (19.2%) for sildenafil and isosorbide nitrates.

Limitations of the study include the fact that there were no physician identifiers and no indication whether patients actually took the medications. Also, because this patient population had private insurance, they tend to be younger and have fewer chronic health conditions, so the data set may actually be underestimating the true prevalence of this problem in the general population, Dr. Scales told Urology Times.