Abstract
BACKGROUND: Clinical study and practice data have shown sildenafil improves sexual function in men with erectile dysfunction (ED). However, some men treated with placebo in double-blind, placebo-controlled sildenafil studies also report improved erectile function as measured by International Index of Erectile Function (IIEF)-Erectile Function Domain (EFD) scores. AIM: This analysis estimated the relationship between post-baseline IIEF-EFD scores and demographic variables, including co-morbidities, in men with ED receiving placebo in flexible-dose sildenafil studies. METHODS: Placebo-treated participants in the intent-to-treat population of 42 double-blind, placebo-controlled, flexible-dose, sildenafil studies were included. A participant was classified as a placebo responder if the IIEF-EFD score was ≥26 at the last visit. OUTCOMES: Variables assessed were age (<45, 45-64, ≥65 years), race, body mass index, co-morbidities (cardiovascular disease/hypertension, diabetes mellitus, depression), date the last study dose was taken, study completion date, ED etiology (psychogenic, organic, mixed), history of cigarette smoking, ED duration, baseline IIEF-EFD score (≤10, 11-16, ≥17), and treatment duration. Stepwise multivariate logistic regression models assessed the odds of being a responder vs a non-responder for each variable. RESULTS: A total of 4,360 men were included; 13.5% were responders. Odds estimates indicated the largest likelihood of placebo response occurred in men who were black (odds = 20.2, P < .0001), were younger than 45 years (odds = 7.3, P < .0001), had mild ED (baseline IIEF-EFD ≥17; odds >100, P < .0001), and did not have diabetes (odds = 4.5, P < .0001). The likelihood of a placebo response decreased as ED duration increased (odds = 0.74, P < .0001). The frequency of common adverse events was similar between placebo responders and non-responders. CLINICAL TRANSLATION: These findings contribute to the improved understanding of predictors of placebo response in sildenafil clinical studies. Elucidation of these factors may contribute to the development of further interventions and treatment strategies and best practices for clinical trials. STRENGTHS AND CONCLUSIONS: Strengths of this analysis include the large and diverse population and the duration of follow-up. Limitations include those associated with retrospective analyses and the inability to ascertain to what extent other demographic factors might have contributed to the placebo responses or how these placebo responses might be related to the natural course of ED. CONCLUSIONS: Certain demographics, co-morbidities, and condition characteristics predicted the odds of a placebo response in sildenafil clinical studies of ED. Underlying reasons behind a placebo response warrant further evaluation. Mulhall JP, Carlsson M, Stecher V, et al. Predictors of Erectile Function Normalization in Men With Erectile Dysfunction Treated With Placebo. J Sex Med 2018;15:866-872.