Rationale for combination therapy of intraurethral prostaglandin E1 and sildenafil in the salvage of erectile dysfunction patients desiring noninvasive therapy

Corpus cavernosum smooth muscle relaxation and hence penile erection are regulated in part by increases in smooth muscle synthesis of the second messengers cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). The object of this study was to determine 30-month follow-up results in motivated patients desiring noninvasive medical therapy using sildenafil citrate (Viagra) in combination with intraurethral prostaglandin E(1) (PGE(1)) (Medicated Urethral System for Erection [MUSE]). Twenty-eight patients (mean +/- s.d. age, 59 +/-7.3 y; 17 who had undergone radical prostatectomy and 11 who had a diagnosis of organic erectile dysfunction) were included in this study. Detailed history taking and physical examinations were performed and vascular risk factors noted. In these patients, treatment with either 100 mg of sildenafil citrate and/or 1000 microg of MUSE had failed. None of these patients desired intracavernosal injection. Duplex Doppler ultrasonography after redosing was carried out on all patients. Dynamic infusion corpus cavernosography/cavernosometry was obtained in 17 of 28 patients, and combination therapy was initiated using 100 mg of sildenafil citrate orally 60 min before intercourse and 500 microg of MUSE intraurethrally immediately before intercourse. Independently, either 100 mg of sildenafil citrate or 1000 microg of MUSE was not efficacious in inducing an erection sufficient for vaginal penetration in any of the 28 patients. After initiating a combination therapy, at 30 months, all 28 patients were reporting erections sufficient for vaginal penetration, with 3.6 intercourse episodes per month. None of the patients crossed over to intracavernosal therapy or penile prosthesis. During therapy, eight of 28 patients reduced the dose of sildenafil citrate to 50 mg. Combination therapy with MUSE and sildenafil may be more efficacious in the salvage of patients who desire noninvasive therapy but in whom single-treatment modalities fail. Although both cAMP- and cGMP-mediated vasodilation can lead to penile erection, combining therapies that incorporate both pathways may succeed when single therapies fail.