A PROSTAGLANDIN-E1 DOSE-RESPONSE STUDY IN MAN

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 dagger 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 20 mug. demonstrated a steep dose-dependent increase; at greater than 20 mug. a plateau was reached, indicating a nonlinear response. More than 80% of the patients attained the maximal response at doses of 20 mug. 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 20 mug. or less, since larger amounts offer little additional benefit.