Objective: To evaluate, posthoc, the relationship between serum total testosterone and response to therapy in a study of tadalafil once daily for erectile dysfunction (ED).
Methods: Men were aged ≥18 years, with ≥3-month history of ED and partial prior response to on-demand (PRN) phosphodiesterase type 5 inhibitor (PDE5I) therapy. A 4-week maximum-dose PRN PDE5I run-in was followed by a 4-week nondrug washout period, then randomization to tadalafil 2.5 mg titrated to 5 mg or tadalafil 5 mg (pooled for analyses) or placebo once daily for 12 weeks. Analyses compared endpoint efficacy results between low- (<300 ng/dL) vs normal-testosterone (≥300 ng/dL) level subgroups.
Results: Improvements for tadalafil vs placebo were significant for the International Index of Erectile Function (IIEF) Erectile Function domain, Intercourse Satisfaction domain, Overall Satisfaction domain, and Question 15 (confidence in the ability to get and keep an erection; all P<.001), and for the Sexual Encounter Profile Questions 1-5 (all P≤.011). Analysis of covariance modeling identified significant treatment-by-subgroup interactions for the IIEF-Overall Satisfaction domain and erection confidence question and Sexual Encounter Profile Question 3. Comparing between tadalafil-treated testosterone subgroups, the IIEF-Erectile Function domain scores improved significantly more in men with normal vs low testosterone (P=.022); no other significant differences were identified for either placebo or tadalafil. No significant differences in pre-existing conditions were observed between tadalafil and placebo within the normal- and low-testosterone subgroups.
Conclusion: In men with partial response to a PRN PDE5I, tadalafil 5 mg once daily significantly improved ED and sexual function vs placebo irrespective of testosterone levels.
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