Background: Despite widespread adoption of the six-item erectile function (EF) domain of the International Index of Erectile Function (IIEF) as a clinical trial end point, there are currently no objective data on what constitutes a minimal clinically important difference (MCID) in the EF domain.

Objective: Estimate the MCID for the IIEF EF domain.

Design, setting, and participants: Anchor-based MCIDs were estimated using data from 17 randomized, double-blind, placebo-controlled, parallel-group clinical trials of the phosphodiesterase type 5 inhibitor (PDE5-I) tadalafil for 3345 patients treated for 12 wk.

Measurements: The anchor for the MCID is the minimal improvement measure calculated using change from baseline to 12 wk on IIEF question 7: "Over the past 4 weeks, when you attempted sexual intercourse how often was it satisfactory for you?" MCIDs were developed using analysis of variance (ANOVA)- and receiver operating characteristic (ROC)-based methods in a subset of studies (n=11) by comparing patients with and without minimal improvement (n=863). MCIDs were validated in the remaining six studies (n=377).

Results and limitations: The ROC-based MCID for the EF domain was 4, with estimated sensitivity and specificity of 0.74 and 0.73, respectively. MCIDs varied significantly (p<0.0001) according to baseline ED severity (mild: 2; moderate: 5; severe: 7). MCIDs consistently distinguished between patients in the validation sample classified as no change or minimally improved overall and by geographic region, ED etiology, and age group. MCIDs did not differ by age group, geographic region, or ED etiology. Current analyses were based on 17 clinical trials of tadalafil. Results need to be replicated in studies using other PDE5-Is or in nonpharmacologic intervention studies.

Conclusions: The contextualization of treatment-related changes in terms of clinically relevant improvement is essential to understanding treatment efficacy, to interpreting results across studies, and to managing patients effectively. This analysis provides, for the first time, anchor-based estimates of MCIDs in the EF domain score of the IIEF.