Erectile dysfunction - PT-141
When Pfizer introduced Viagra (sildenafil) into the market, it effectively invented a new disease - erectile dysfunction (ED). Impotence, once a taboo subject, instantly became a common topic of conversation, and numerous other companies piled into the area looking for a share of this new market.
Another product to treat erectile dysfunction is being developed by Palatin Technologies. PT-141 is a synthetic heptapeptide agonist of a-MSH, and is an agonist at the melanocortin receptors, including MC3R, which are primarily found in the central nervous system.1 This is different from the mechanism of action of Viagra and the other phosphodiesterase 5 inhibitors, which act on the vascular system.
In a double blind, placebo-controlled Phase I study, healthy male subjects and patients with Viagra-responsive erectile dysfunction were given PT-141 or placebo intranasally.2 In both cases, the erectile response induced by PT-141 administration was statistically significant at doses greater than 7mg, and the onset of the first erection occurred in around 30 minutes. The only adverse effects were mild or moderate.
A trial has also been carried out in male subjects whose response to Viagra was inadequate.3 Doses ranging from 0.3 to 10mg were given subcutaneously to these subjects, plus a group of healthy males. Statistically significant erectile response was achieved with doses greater than 1mg. ED patients were then treated with placebo, 4 or 6mg of PT-141 in a crossover design. Both doses gave a statistically significant erectile response.
A further trial has investigated the co-administration of Viagra and PT-141 to look at potential synergistic effects. Patients in the double blind randomised placebo-controlled three way crossover study were given 25mg Viagra by tablet and 7.5mg PT-141 by intranasal spray, 25mg Viagra and a placebo intranasal spray, or two placebos. Patients given both drugs had, on average, increased erectile activity compared with those given Viagra alone or placebo only.
Recently, Palatin reported positive results of a Phase IIa pilot study in pre-menopausal women diagnosed with female sexual dysfunction. A total of 18 women were given two 10mg doses of PT-141 or placebo by intranasal spray in a randomised double blind placebo-controlled crossover clinical study. Subjects given the drug reported increases in their levels of sexual desire and genital arousal compared with placebo. Trials continue in both men and women.