Daily use of tadalafil does not result in improved erectile function amongst men undergoing radiotherapy for prostate cancer, according to a study published on April 2 by the Journal of the American Medical Association.

Prostate cancer treatment often leads to erectile dysfunction (ED), resulting in dissatisfaction with radiotherapy and detrimental effects on phsychosocial function in patients and their partners. The cause of ED after treatment is unknown, but many believe that penile endothelial dysfunction with cavernosal hypoxia and fibrosis is the culprit. To address this issue, phosphodiesterase-5 inhibitors are regularly administered to patients. Tadalafil has been reputed to improve the situation, and its special pharmacokinetic properties enable steady-state exposure.

Lead author Thomas M. Pisansky, MD, of the Mayo Clinic in Rochester, Minn., and colleagues conducted a placebo-controlled, double-blinded, parallel-group study to identify tadalafil’s ability to manage spontaneous erectile dysfunction in 221 men who are treated with radiotherapy for prostate cancer. Participants then reported International Index of Erectile Function responses before radiotherapy, at two weeks, four weeks, between weeks 20 and 24, between weeks 28 and 30, and at one year. Those involved and their partners could also answer a Sexual Adjustment Questionnaire and the Locke Marital Adjustment test at these time periods.

Of the study’s participants, 121 were assigned to take five milligrams of tadalalfil daily and 121 were assigned a placebo for 24 weeks. The results revealed that 80 in the tadalafil group retained erectile function between weeks 28 and 30 in comparison to 61 from the placebo group. The absolute difference was five percent.

Moreover, a significant difference was not observed by the researchers at one year between the two groups, with 72 percent from the pharmaceutical group retaining erectile function versus 71 percent in the placebo group.

Tadalafil was not associated with significant improvement in overall sexual function or satisfaction. Additionally, partners of patients assigned to the tadalafil group did not find a significant effect on sexual satisfaction or an improvement in marital adjustment.

“Based on evidence available presently, there is no support for phosphodiesterase-5 inhibitor use to prevent ED after highly conformal external radiotherapy or low-dose-rate brachytherapy,” wrote Pisansky and colleagues. “Alternative strategies to prevent ED in this context appear warranted, perhaps with attention toward alternative dosing, investigation of neuroprotective interventions, or further refinements of radiotherapy delivery methods.”