A PROSTAGLANDIN-E1 DOSE-RESPONSE STUDY IN MAN

Because prostaglandin E1 causes erection by smooth muscle relaxation i n a receptor-dependent manner, one would expect increasing dosages to cause a progressively greater response and that, at receptor saturatio n, further increases would not be beneficial. To test this hypothesis a single-blind, placebo-controlled study of increasing dosages of pros taglandin E1 injected intracavernously was done. In 16 men with vascul ogenic impotence erections were monitored by the RigiScan dagger devic e in real time for 2 hours after injection, and rigidity, tumescence a nd duration of erection were measured. Summary parameters to character ize erection with each dosage were developed: maximal rigidity, maxima l rigidity sustained for 30 minutes and duration of greater than 60% r igidity. 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 t han 80% of the patients attained the maximal response at doses of 20 m ug. or less and less than 20% benefited from a further increase. Based on these results, the effects of prostaglandin E1 appear to be recept or-dependent and prostaglandin E1 monotherapy for impotence could be l imited to 20 mug. or less, since larger amounts offer little additiona l benefit.