A Prostaglandin E1 Dose-Response Study in Man

Abstract

Because prostaglandin E1 causes erection by smooth muscle relaxation in a receptor-dependent manner, one would expect increasing dosages to cause a progressively greater response and that, at receptor saturation, further increases would not be beneficial. To test this hypothesis a single-blind, placebo-controlled study of increasing dosages of prostaglandin E1 injected intracavernously was done. In 16 men with vasculogenic impotence erections were monitored by the RigiScan††Dacomed, Minneapolis, Minnesota. device in real time for 2 hours after injection, and rigidity, tumescence and duration of erection were measured. Summary parameters to characterize erection with each dosage were developed: maximal rigidity, maximal rigidity sustained for 30 minutes and duration of greater than 60% rigidity. The dose-response curve was similar for all 3 parameters. The initial response to escalating doses of prostaglandin E1 from 2.5 to 20μg. demonstrated a steep dose-dependent increase; at greater than 20μg. a plateau was reached, indicating a nonlinear response. More than 80% of the patients attained the maximal response at doses of 20μg. or less and less than 20% benefited from a further increase. Based on these results, the effects of prostaglandin E1 appear to be receptor-dependent and prostaglandin E1 monotherapy for impotence could be limited to 20μg. or less, since larger amounts offer little additional benefit.