Switching patients with erectile dysfunction from sildenafil citrate to tadalafil: results of a European multicenter, open-label study of patient preference

Clin Ther. 2003 Nov;25(11):2724-37. doi: 10.1016/s0149-2918(03)80329-6.


Background: Three inhibitors of phosphodiesterase 5 (PDE5) are now available for the treatment of erectile dysfunction (ED): sildenafil citrate, vardenafil, and tadalafil. Pharmacologic differences between these compounds may result in patient preferences for one over another and may influence treatment decisions made by the physician and patient. Therefore, clinical research is needed to investigate whether individual properties of the PDE5 inhibitors play a role in shaping patient preference.

Objectives: The goal of this study was to determine what proportion of ED patients currently taking sildenafil would, after a period of treatment with tadalafil, elect to resume treatment with sildenafil at the customary dose and what proportion would elect a switch to tadalafil 20 mg for a longer period. The tolerability of both treatments was also investigated.

Methods: This was a short-term, multicenter, open-label, 1-way crossover trial conducted in Sweden and Italy. Eligible patients included men aged >or=18 years with a minimum 3-month history of ED who had been taking sildenafil at stable fixed doses of 25, 50, or 100 mg as needed for at least 6 weeks and up to 24 weeks. The study consisted of 6 phases: a 1-week screening phase, a 3-week sildenafil assessment phase, a 1-week washout phase, a 6-week tadalafil initiation phase, a 3-week tadalafil assessment phase, and a 6-month extension phase, during which patients received their treatment of choice free of charge. The primary outcome measure was the proportion of patients electing to take sildenafil or tadalafil during the extension phase.

Results: Of 155 men enrolled, 147 (97.8%) completed the assessment phases of the trial. Of these 147 men, 133 (90.5%) elected to receive tadalafil in the 6-month extension phase and 14 (9.5%) elected to receive sildenafil (P < 0.001). The proportions preferring tadalafil to sildenafil were similar irrespective of age group (>or=50 years, 92%; <50 years, 90%), severity of ED (mild, 95%; moderate, 88%; severe, 96%), etiology of ED (psychogenic, 94%; organic, 91%; mixed, 87%), and sildenafil dose at study entry (50 mg, 90%; 100 mg, 89%). Both medications were well tolerated. The most common treatment-emergent adverse events occurring in >or=2% of patients during the tadalafil assessment phase included headache (4.8%), nasal congestion (4.1%), dyspepsia (3.4%), flushing (2.7%), back pain (2.0%), diarrhea (2.0%), and nausea (2.0%); the most common treatment-emergent adverse events during the sildenafil assessment phase were flusing (7.1%), nasal congestion (6.5%), headache (4.5%), and nasopharyngitis (3.2%).

Conclusions: In this short-term, open-label study, patients who were currently taking sildenafil for ED and then received tadalafil preferred to continue oral therapy with tadalafil over sildenafil by a ratio of approximately 9:1. Although the study sought to mimic the experience of actual patients receiving treatment for ED, the results are subject to potential limitations due to the design of the study, which included differences in dosing instructions and dosages for sildenafil and tadalafil. Both sildenafil and tadalafil were well tolerated.

Publication types

  • Clinical Trial
  • Controlled Clinical Trial
  • Multicenter Study

MeSH terms

  • 3',5'-Cyclic-GMP Phosphodiesterases / antagonists & inhibitors*
  • Aged
  • Carbolines / adverse effects
  • Carbolines / therapeutic use*
  • Cross-Over Studies
  • Cyclic Nucleotide Phosphodiesterases, Type 5
  • Erectile Dysfunction / drug therapy*
  • Humans
  • Italy
  • Male
  • Middle Aged
  • Patient Satisfaction
  • Piperazines / adverse effects
  • Piperazines / therapeutic use*
  • Prospective Studies
  • Purines
  • Sildenafil Citrate
  • Sulfones
  • Sweden
  • Tadalafil


  • Carbolines
  • Piperazines
  • Purines
  • Sulfones
  • Tadalafil
  • Sildenafil Citrate
  • 3',5'-Cyclic-GMP Phosphodiesterases
  • Cyclic Nucleotide Phosphodiesterases, Type 5
  • PDE5A protein, human