Tolerance to the therapeutic effect of tadalafil does not occur during 6 months of treatment: A randomized, double-blind, placebo-controlled study in men with erectile dysfunction.

Introduction: Tolerance can cause a decrease in drug efficacy during chronic therapy, possibly leading to treatment failures.

Aim: The aim of this article is to determine whether tolerance developed to the effects of tadalafil on erectile function (EF) over a 6-month treatment period.

Methods And Main Outcome Measures: Post hoc analysis of data from a multicenter, double-blind, randomized, placebo-controlled, parallel group study was performed. Men (> or =18 years of age) with erectile dysfunction (ED) were randomized to treatment with placebo (N = 47) or 20-mg tadalafil (N = 93) taken as needed for 6 months. This report focuses on efficacy assessed with the Sexual Encounter Profile (SEP) diary (diaries were collected after a 4-week treatment-free run-in period [baseline], and monthly for 6 months), and with the International Index of Erectile Function (IIEF) (administered at baseline, and at 3 and 6 months). RESULTS. The mean per-patient percentage "yes" response on SEP question 3 (SEP3, successful intercourse) was 33 +/- 4% at baseline, 74 +/- 4% after 1 month, and 78 +/- 4% after 6 months of tadalafil treatment. The IIEF EF domain score was 16.2 +/- 0.7 at baseline, 24.3 +/- 0.8 after 3 months, and 24.3 +/- 0.9 after 6 months of tadalafil treatment. In a subgroup of patients who took tadalafil > or =3 times per week (N = 24), the SEP3 score was 87 +/- 4% after 1 month and 93 +/- 3% after 6 months of treatment, and the IIEF EF domain score was 27.3 +/- 0.9 after 3 months and 28.5 +/- 0.4 after 6 months. Of 16 tadalafil-treated patients who discontinued, three cited a lack of efficacy.

Conclusions: Tadalafil treatment significantly improved SEP3 and IIEF EF domain scores. The efficacy of tadalafil, taken as needed, was maintained over a 6-month treatment period in men with ED.