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Broderick GA, Donatucci CF, Hatzichristou D, Torres LO, Valiquette L, Zhao Y, Loughney K, Sides GD, Ahuja S. Efficacy of tadalafil in men with erectile dysfunction naive to phosphodiesterase 5 inhibitor therapy compared with prior responders to sildenafil citrate. J Sex Med 2006;3:668-675.

Clinical trials that utilise the phospodiesterase-5 inhibitor tadalafil tend to exclude patients who have previously been non-responders to sildenafil citrate (Sildenafil). This retrospective analysis of 14 previous tadalafil studies, utilising the pooled data, attempts to identify the impact this has on these studies by making some basic assumptions.

1349 patients who were naïve to sildenafil were compared with 1440 patients who had previously responded to sildenafil. It makes a reasonable assumption that the group naïve to sildenafil would consist of a mixture of patients that would respond and those that would be non-responders. The data was from trials with a 4-week, treatment-free, run-in period and then double-blind, parallel-group, placebo-controlled phase with Tadalafil 10mg or 20mg for 12 weeks dosed as required.

Tadalafil improved erectile function compared with placebo in both naïve patients and sildenafil prior responders (P<0.001). The differences in the efficacy outcome for both groups (International Index of Erectile function, Sexual Encounter Profile diary questions 2-5, Overall and Intercourse Satisfaction, Global Assessment Question) were not statistically significant (P>or=0.10). The conclusion drawn from this, suggestion rather than proof, is that the exclusion of sildenafil non-responders in previous clinical trials may not have substantially affected efficacy outcomes, which is an interesting point when it comes to the design of future studies.