FRANKFURT (Reuters) - Patients with erectile dysfunction prefer rival drugs over the pioneering treatment, Pfizer's Viagra (sildenafil), show two studies to be presented at a meeting of sexual medicine researchers.

Cialis (tadalafil), a drug marketed by Lilly-ICOS, a joint venture between Eli Lilly and ICOS Corp, emerged as the top option in one trial, and Levitra (vardenafil), sold by Bayer and GlaxoSmithKline led its rivals in the other.

The studies are being presented at the sixth congress of the European Society for Sexual Medicine in Istanbul on Monday.

Excerpts from a study of 150 patients carried out by Hamburg urologist Hartmut Porst showed that 45% of patients preferred Cialis, 30% Levitra and 13% Viagra. Twelve percent had no preference.

"The overwhelming majority of the patients prefer the two new drugs with tadalafil being ahead due to its long duration of action," the study authors said.

Another study, led by Frank Sommer at the University Medical Centre in Cologne, showed that 43% of men in a high dose, three-way preference trial preferred Levitra. Forty percent of the patients preferred Cialis and 17% preferred Viagra.

Levitra was also found to be the preferred option at a lower, initial dose, with Viagra second and Cialis third.

Currently 86 men have completed the maximum dose trial and 47 the lower dose trial.

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