The authors of the new research specifically examined how frequently phosphodiesterase type 5 (PDE5) inhibitors, such as Viagra, were prescribed. The U.S. Food and Drug Administration and the European Medicines Agency have warned that these drugs for erectile dysfunction are contraindicated for use with nitrates because of concerns about cardiovascular risks.
“Small, randomized, pharmacologic studies have reported an amplified decrease in blood pressure during controlled coexposure with nitrates and [phosphodiesterase type 5 inhibitors], both in healthy participants and in participants with IHD,” wrote lead author Anders Holt, MD, of Copenhagen University Hospital–Herlev and Gentofte and colleagues, in Annals of Internal Medicine. “Potentially, this increases the risk for vascular ischemic events including myocardial infarction and stroke.”
But there is a scarcity of real-world data showing that using both types of drugs together increase these risks, the researchers noted.
To address this knowledge gap, Dr. Holt and colleagues conducted a retrospective study involving 249,541 Danish men with IHD. In this overall population, from 2000 to 2018, prescriptions for PDE5 inhibitors increased 10-fold, from 3.1 to 30.9 prescriptions per 100 persons per year. Within a subgroup of 42,073 patients continuously prescribed oral organic nitrates, PDE5-inhibitor prescriptions jumped twice that magnitude, from 0.9 to 19.7 prescriptions per 100 persons per year.
Despite this surge in coprescribing, the investigators did not observe a significant increase in either of two composite measures of cardiovascular adverse events. The first composite included ischemic stroke, shock, cardiac arrest, myocardial infarction, or acute coronary arteriography (odds ratio, 0.58; 95% confidence interval, 0.28-1.13). The second composite included drug-related adverse events, angina pectoris, or syncope (OR, 0.73; CI, 0.40-1.32).
Lead author speculates on reasons for findings
“I propose several explanations [for these findings],” Dr. Holt said in an interview, “but I want to emphasize that our study does not contain any data to back it up. It is just speculation. First, the observed drop in blood pressure may not cause a condition for which patients seek a hospital. A drop in blood pressure has been shown in pharmacologic trials, but it might not translate to a real-life risk for cardiovascular outcomes. Second, patients could be well informed and adherent to guidance that the prescribing physician has provided. For example, patients are aware of the recommended pause in nitrate treatment before PDE5-inhibitor use and follow these recommendations. Third, nitrates are often taken in the morning, and with the careful assumption that most PDE5-inhibitor activities take place in the evening, the nitrates could be metabolized to a degree such that the synergistic interaction is negligible.”
Dr. Holt went on to suggest a novel clinical approach based on the new findings.
“Coadministration should still be contraindicated due to the proven drop in blood pressure,” he said. “However, perhaps physicians can allow for coprescription if patients are adequately informed.”
A qualitative study is needed to determine how patients and physicians discuss coprescription, including avoidance of coadministration, Dr. Holt added.