Aim: To study the effect of intracavernous sodium nitroprusside (SNP), a nitric oxide (NO) donor, on penile erection. Methods: Forty-two patients with erectile dysfunction (ED) were randomly assigned to receive SNP 300 g or the control drugs (papaverine 30 mg + phentolamine 1 mg) intracavernously crosswise one week apart. The penile length, circumference and hardness after the administration of the experimental and control drugs were assessed and compared statistically. Results: (1) There was no significant difference between the changes in penile length and circumference in the two occasions; (2) In 25 SNP and 28 control cases, the hardness of the penis was scored above 100 as evaluated by the Virag method (P>0.05); (3) The duration of erection in the controls was longer than that in the SNP, but there were three priapism in the controls and not a single one in the SNP; (4) there was no apparent change in the heart rate and blood pressure in both occasions; other side effects were minimal except slight local pain in a few controls. Conclusion: SNP facilitates relaxation of the penile smooth muscle and penile erection without significant side effects. SNP may be used in ED patients that experience pain and priapism with papaverine/phentolamine.

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