Papaverine (Pavabid) is a nonspecific phosphodiesterase inhibitor that increases cAMP and cGMP levels in penile erectile tissue. Papaverine is particularly known as a smooth muscle relaxant and vasodilator. Its principal pharmacological action is as a nonspecific vasodilator of smooth muscles of the arterioles and capillaries. Various vascular beds and smooth muscle respond differently to papaverine administration both in intensity and duration. Papaverine decreases the resistance to arterial inflow and increases the resistance to venous outflow.
Papaverine is highly effective in men with psy-chogenic and neurogenic ED but less effective in men with vasculogenic ED. Papaverine-phentolamine combinations have been used in self-injection procedures. Papaverine doses may range from 15 to 60 mg. Papa verine treatment in patients with severe arterial or venous incompetence is usually unsuccessful, but autoinjections using low doses sufficient to achieve an erection are safe and efficient.
Major side effects associated with papaverine therapy include priapism, corporeal fibrosis, and occasional increases in serum aminotransferases. Intracorporeal scarring may be related to the low pH of the vehicle that is necessary to solubilize papaverine. Attempts to buffer papaverine to render it more suitable for intracaver-nosal injection have not been entirely satisfactory, and such delivery may still lead to intracorporeal scarring.
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