citrate is a white to off-white crystalline powder with a solubility of 3. Sildenafil at steady state (80 mg t. Sildenafil was not carcinogenic when administered to rats for 24 months at a dose resulting in total systemic drug exposure (AUCs) for unbound sildenafil and its major metabolite of 29- and 42-times, for male and female rats, respectively, the exposures observed in human males given the Maximum Recommended Human Dose (MRHD) of 100 mg. Sildenafil was not carcinogenic when administered to mice for 18-21 months at dosages up to the Maximum Tolerated Dose (MTD) of 10 mg/kg/day, approximately 0. Sildenafil was negative in in vitro bacterial and Chinese hamster ovary cell assays to detect mutagenicity, and in vitro human lymphocytes and in vivo mouse micronucleus assays to detect clastogenicity. Sildenafil has no direct relaxant effect on isolated human corpus cavernosum, but enhances the effect of nitric oxide (NO) by inhibiting phosphodiesterase type 5 (PDE5), which is responsible for degradation of cGMP in the corpus cavernosum. Sildenafil at recommended doses has no effect in the absence of sexual stimulation. Sildenafil is only about 10-fold as potent for PDE5 compared to PDE6, an enzyme found in the retina which is involved in the phototransduction pathway of the retina. Sildenafil and its major circulating N-desmethyl metabolite are both approximately 96% bound to plasma proteins. Sildenafil is used to treat male sexual function problems (impotence or erectile dysfunction) by blocking a certain enzyme (phosphodiesterase-PDE5) in the body. Sildenafil is a selective inhibitor of cGMP specific phosphodiesterase type 5 (PDE5) which is responsible for degradation of cGMP in the corpus cavernosum. Sildenafil has no direct relaxant effect on isolated human corpus cavernosum but enhances the relaxant effect of NO on this tissue. Sildenafil (Viagra) is a prescription medication used to treat erectile dysfunction. Sildenafil Citrate (Generic Viagra) belongs to a group of medicines that delay the enzymes called phosphodiesterases from working too quickly. Sildenafil Citrate is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil Citrate is an oral drug for male impotence, also known as erectile dysfunction (ED).