The Role of Initial Success Rates and Other Factors in Determining Reliability of Outcomes of Phosphodiesterase Inhibitor Therapy for Erectile Dysfunction: A Pooled Analysis of 17 Placebo-Controlled Trials of Tadalafil for Use as Needed Angelina Sontag, PhD,* Raymond C. Rosen, PhD, † Heather J. Litman, PhD, † Xiao Ni, PhD,* and Andre B. Araujo, MA † *Eli Lilly and Company, Indianapolis, IN, USA; † New England Research Institutes, Inc., Watertown, MA, USA DOI: 10.1111/j.1743-6109.2012.02901.x ABSTRACT Introduction. Reliability of successful outcomes in men with erectile dysfunction (ED) on phosphodiesterase type 5 inhibitors is an important aspect of patient management. Aims. We examined reliability of successful outcomes in a large integrated dataset of randomized tadalafil trials. Main Outcome Measures. Success rates, time to success, subsequent success after first success, and probability of success were analyzed based on Sexual Encounter Profile questions 2 and 3. Methods. Data from 3,254 ED patients treated with tadalafil 10 mg (N = 510), 20 mg (N = 1,772), or placebo (N = 972) were pooled from 17 placebo-controlled studies. Results. Tadalafil patients had significantly higher first-attempt success rates vs. placebo. This effect was consistent across most subgroups; however, patients with severe ED experienced a greater response to tadalafil than patients with mild–moderate ED. Approximately 80% of patients achieved successful penile insertion within two attempts with either tadalafil dose and successful intercourse within eight attempts for tadalafil 10 mg and four attempts for tadalafil 20 mg. However, approximately 70% of tadalafil-treated patients achieved successful intercourse even by the second attempt. Subsequent success rates were higher for patients with first-attempt success (81.5% for 10 mg and 86.1% for 20 mg vs. 66.2% for placebo, P < 0.001) vs. patients with later initial success (53.2% for 10 mg and 56.4% for 20 mg vs. 39.9% for placebo, P < 0.001). Among patients treated with tadalafil, intercourse success rates at early attempts were similar to rates at later attempts (i.e., attempts 5 and 10 vs. 25), although insertion success rates were significantly lower earlier in treatment. Conclusions. The findings affirm the reliability of successful outcomes with tadalafil treatment and that first-attempt success is a critical factor affecting subsequent outcomes. The results further show that even among men who did not succeed on first attempt, a substantial proportion will have successful outcomes if treatment is maintained. Sontag A, Rosen RC, Litman HJ, Ni X, and Araujo AB. The role of initial success rates and other factors in determining reliability of outcomes of phosphodiesterase inhibitor therapy for erectile dysfunction: A pooled analysis of 17 placebo-controlled trials of tadalafil for use as needed. J Sex Med **;**:**–**. Key Words. Erectile Dysfunction; Phosphodiesterase Type 5 Inhibitors; PDE5; Tadalafil; Reliability of Efficacy; Pooled Analysis Introduction E rectile dysfunction (ED) is a widespread health problem estimated to affect approxi- mately 300 million men worldwide by 2025 [1]. Phosphodiesterase type 5 (PDE5) inhibitors are safe and effective treatments and are recom- mended as a first line of therapy for treatment of ED [2]. Yet, despite the broad efficacy and safety of these agents, discontinuation of PDE5 inhibitor treatment is relatively high [3]. One reason postu- lated for the discontinuation of PDE5 therapy in 1 © 2012 International Society for Sexual Medicine J Sex Med **;**:**–**