Efficacy and safety of tadalafil 20 mg on demand vs. tadalafil 5 mg once-a-day in the treatment of post-radiotherapy erectile dysfunction in prostate cancer men: a randomized phase II trial

J Sex Med. 2010 Aug;7(8):2851-9. doi: 10.1111/j.1743-6109.2010.01890.x.


Introduction: The role of phosphodiesterase type 5 inhibitors in the treatment of post-radiotherapy erectile dysfunction (ED) has not been extensively investigated.

Aim: To compare the efficacy and safety of on-demand 20-mg tadalafil (arm A) with the newly released tadalafil 5-mg once-a-day dosing (arm B) in patients with ED following radiotherapy for prostate cancer (PC).

Methods: Randomized study to receive on-demand 20-mg or once-a-day 5-mg tadalafil for 12 weeks. Main Outcome Measures. Changes in the International Index of Erectile Function (IIEF) domain scores and Sexual Encounter Profile (SEP) question 2 and 3 positive response rates.

Results: Fifty-two out of 86 screened patients were randomized. Forty-four patients were evaluable for efficacy. A significant improvement in all domains of the IIEF was observed in both arms (P = 0.0001) with mean erectile function domain scores values of 25 and 27.1 for the 20-mg and 5-mg tadalafil, respectively (P = 0.19). SEP 2 and 3 positive response rates increased from 0% in both arms at baseline to 81% and 70% in the 20-mg arm and 90% and 73% in the 5-mg arm, respectively, at the end of treatment (P = 0.27). End of treatment global efficacy question positive answers were 86% in the 20-mg arm and 95% in the 5-mg arm (P = 0.27). Higher treatment compliance was shown in arm B (100%) as compared with arm A (86%). There was a nonstatistically significant trend toward fewer side effects in favor of the 5-mg daily dose arm.

Conclusions: In the study population, both tadalafil formulations generated significantly high response rates according to the outcome measures and were well tolerated. The once-a-day 5-mg dosing showed higher compliance and marginally reduced side effects, thus making it an attractive alternative to on-demand therapy for ED in post-radiotherapy PC patients.

Publication types

  • Clinical Trial, Phase II
  • Comparative Study
  • Randomized Controlled Trial

MeSH terms

  • Aged
  • Aged, 80 and over
  • Carbolines / administration & dosage*
  • Carbolines / adverse effects
  • Delayed-Action Preparations
  • Dose-Response Relationship, Drug
  • Drug Administration Schedule
  • Erectile Dysfunction / drug therapy*
  • Erectile Dysfunction / psychology
  • Humans
  • Male
  • Medication Adherence / psychology
  • Middle Aged
  • Neoplasm Staging
  • Penile Erection / drug effects
  • Penile Erection / psychology
  • Penile Erection / radiation effects
  • Phosphodiesterase 5 Inhibitors / administration & dosage*
  • Phosphodiesterase 5 Inhibitors / adverse effects
  • Prostatic Neoplasms / pathology
  • Prostatic Neoplasms / radiotherapy*
  • Radiation Injuries / drug therapy*
  • Radiation Injuries / psychology
  • Radiotherapy, Conformal / adverse effects*
  • Tadalafil


  • Carbolines
  • Delayed-Action Preparations
  • Phosphodiesterase 5 Inhibitors
  • Tadalafil