Erectile dysfunction (ED) is a common complication of diabetes mellitus. In four independent, 12-week, randomised, placebo-controlled clinical trials that evaluated the pro-erectile properties of the selective phosphodiesterase type 5 (PDE-5) inhibitors, sildenafil (Viagra) (25—100 mg), tadalafil (10 and 20 mg) and vardenafil (10 and 20 mg) in men with ED secondary to diabetes mellitus, all the active drugs were significantly superior to placebo. In this difficult-to-treat population, the greatest difference from placebo for the overall responder rate of diabetic men reporting improved erections occurred with vardenafil 20 mg (72% vs. 13% for placebo).
All the PDE-5 inhibitors were generally well tolerated. There were fewer reports of visual disturbance with vardenafil or tadalafil than with sildenafil, which may be due to their greater selectivity for PDE-5 inhibition and less cross-reactivity with retinal PDE-6 inhibition.
The studies suggest there may be significant differences between the three drugs. However, only head-to-head studies will determine true differences in both efficacy and side effect profile.
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