Comparison of the synergistic effects of tamsulosin versus phentolamine on penile erection: in vitro and in vivo studies.

In vitro and in vivo studies were performed to determine the potential use of tamsulosin (TAM) versus phentolamine (PHE) for intracavernosal injection (ICI) therapy when mixed with papaverine (PAP) and/or prostagladin E1 (PGE1) or with vasoactive intestinal polypeptide (VIP) for the treatment of erectile dysfunction. We performed isometric tension studies on rabbit (n = 15), dog (n = 5), and human (n = 10) cavernous smooth muscle strips with TAM, PAP, PHE, VIP, PGE1, and the combinations of PAP and PHE; PAP and TAM; VIP and PHE; VIP and TAM; PAP, PGE1 and PHE; and PAP, PGE1 and TAM. TAM-containing trimix (PAP 18.75 mg, PGE1 6.25 micromg, and TAM 0.875 mg per ml) or PHE-containing trimix (PAP, PGE1, and PHE 0.625 mg per ml) were also injected into the cavernous bodies of ten mongrel dogs. Among the single agents, TAM and PGE1 (only in human) had the strongest effect on the relaxation of cavernous muscles in rabbit, dog, and human strips (P<0.05). Relaxation responses to 2- or 3-drug mixtures containing tamsulosin were also significantly better (P<0.05) than PHE-containing ones in rabbit, dog, and human strips. The increase in intracavernosal pressure with a TAM-containing trimix was higher than with a PHE-containing one (0.03 ml; 81.2 vs. 75.8 mm Hg, 0.04 ml; 103.2 vs. 94.3 mm Hg), although not statistically different. The drop in systemic blood pressure was lower after injection of a TAM-containing trimix than a PHE-containing one, although not statistically different. In conclusion, tamsulosin might be a more efficacious and safer agent to use for ICI therapy than phentolamine.