Predictors of Response to Sildenafil Citrate Following Radiation Therapy for Prostate Cancer

Phosphodiesterase type 5 inhibitor (PDE5) use is a treatment strategy for prostate cancer patients with post-radiation therapy (RT) erectile dysfunction (ED). To define the predictors of sildenafil response in men treated with RT for prostate cancer. International Index of Erectile Function (IIEF). Patients were enrolled prospectively if they met the following criteria: (i) either a three-dimensional conformal external beam (EBRT) or brachytherapy (BT) with or without androgen deprivation (AD) for prostate cancer; (ii) self-reported ability to have sexual intercourse prior to RT; (iii) experienced onset of ED following RT; (iv) candidates for sildenafil citrate use; (v) followed-up periodically; and (vi) completed the IIEF at least 12 months after RT. Failure to respond to sildenafil was defined as IIEF-erectile function (EF) domain score of < 22. One hundred fifty-two patients met all the criteria: 110 in the EBRT group and 42 in the BT group. Mean age was 62 years. The mean follow-up was 38 months. Mean radiation dose for EBRT was 78 Gy and for BT was 101 Gy. Thirty-five patients received AD, 25% of EBRT, and 62% of BT patients. Sixty-one percent of the patients receiving AD had exposure only pre-RT, whereas 39% had pre- and post-RT AD exposure. The mean duration of AD was 4.6 months. Post-RT IIEF-EF domain score at > 24 months was 17. Successful response to sildenafil occurred in 68% of men at 12 months after RT, 50% at 24 months, and 36% at 36 months. On multivariable analysis, predictors of failure to respond to sildenafil were: older age, longer time after RT, AD > 4 months duration, and RT dose > 85 Gy. Modality of radiation delivery was not predictive of sildenafil failure. A steady decrease in sildenafil response was seen with increasing duration after RT. Several factors were predictive of sildenafil failure. Teloken PE, Parker M, Mohideen N, and Mulhall JP. Predictors of response to sildenafil citrate following radiation therapy for prostate cancer. J Sex Med **;**:**-**.