Eardley I et al. (2005) An open-label, multicentre, randomized, crossover study comparing sildenafil citrate and tadalafil for treating erectile dysfunction in men naïve to phosphodiesterase 5 inhibitor therapy. BJU Int 96: 1323–1332

An open-label, crossover study conducted by Eardley et al. in the UK and Italy compared the effect of two phosphodiesterase-5 inhibitors, sildenafil and tadalafil, on the treatment of erectile dysfunction. After a 4-week pretreatment assessment, 367 men were randomized in a 1:1 ratio to receive sildenafil for 12 weeks followed by tadalafil for 12 weeks, or vice versa, with a 7–10-day washout period between treatments. Patients could choose to alter the treatment dose during the first 8 weeks of treatment in each period. After the completion of both 12-week periods and a 4-day washout period, patients chose which treatment and dose to follow during an 8-week extension. Effectiveness of treatment was assessed by the IIEF scores and the SEP diary.

Sildenafil and tadalafil differ in their pharmacokinetics. The absorption of sildenafil is affected by high-fat foods, while tadalafil is unaffected. Tadalafil has a half-life of 17.5 h, while for sildenafil the half-life is 4–5 h. Patients taking sildenafil were therefore informed that the dose could be taken between 4 h and 30 min before sexual activity, and that food could affect the onset of activity, while those taking tadalafil were advised to take the drug between 12 h and 30 min before sexual activity, and that the effects could last for up to 24 h.

Both drugs were well tolerated, with few patients reporting adverse effects. Of the patients who completed both treatments, 29% chose sildenafil and 71% chose tadalafil for the extension period. For both treatments, large improvements from the baseline were recorded in the IIEF scores and SEP diary.