Evaluating Preference Trials of Oral Phosphodiesterase 5 Inhibitors for Erectile Dysfunction

More treatment options are available now for the treatment of erectile dysfunction (ED) than ever. Treatments include oral phosphodiesterase 5 (PDE5) inhibitors, intracavernosal injections, vacuum constriction devices, and penile implants. Clinicians, researchers, and patients are interested in making direct comparisons between the response of newer treatments and that of established and more developed therapies. Of the currently available treatment options for ED, the most commonly prescribed therapies are oral PDE5 inhibitors, which include sildenafil citrate (Viagra®, Pfizer Inc), tadalafil (Cialis®, Lilly ICOS), and vardenafil (Levitra®, Bayer). However, most patient preference studies of these drugs conducted to date have serious design flaws that hinder interpretation of the data, and thus limit the utility of the results. To make an informed decision on the most appropriate treatment option available, physicians and their patients require a thorough understanding of the methodology of these studies. Clinical comparison or preference trials must establish internal and external validity if the data are to be used in a generalized patient population. We review preference studies that compared sildenafil, tadalafil, and vardenafil, and highlight study designs that can introduce bias. We propose that, like safety and efficacy trials, randomized controlled trials (RCTs) should be the gold standard for evaluating patient preference treatments for ED. We do not wish to discourage individual investigators from performing preference studies, but rather to highlight the features of current preference trials to help patients and clinicians alike become aware of potential biases from independent or industry-sponsored patient preference trials so that they can interpret the results accordingly. Key components of patient preference RCTs are reviewed: period and carryover effects, preference assessments, eligibility criteria, and data analysis. We discuss why these components of patient-preference RCTs are important for evaluating the validity and relevance of patient preference studies. The preference studies discussed in this brief review are summarized in Table 1, and the methodological problems with each study are indicated. We provide a recommendation for the design of such trials that can minimize bias and provide better data for physicians and their patients.