Pharmacokinetic Parameters of a Novel Sildenafil Oral Liquid Suspension Administered to Healthy Adult Men Under Fasted Conditions

Sildenafil citrate is a phosphodiesterase type 5 inhibitor that has been proven safe and effective as an oral therapeutic agent for the treatment of erectile dysfunction. A novel liquid formulation of sildenafil citrate (ASP-001) has been developed as an alternative to currently marketed products. Fifty-six healthy male volunteers were randomized in a prospective, open-label, single center, two-way crossover comparative bioavailability study. Under fasting conditions, each participant received a single 100 mg oral dose of the Test (ASP-001) and Reference (Viagra film-coated tablets) formulations in a randomized sequence with a washout interval of at least 6 days between treatment periods. Blood samples were collected at baseline and up to 24 hours post-dose to assess the pharmacokinetic profile and relative bioavailability of sildenafil and piperazine N-desmethyl-sildenafil. Plasma samples were assayed by a validated LC-MS/MS bioanalytical method specific for sildenafil and piperazine N-desmethyl sildenafil. After single-dose administration, the test formulation ASP-001 was bioequivalent to the tablet form regarding the extent of systemic exposure, but not to the rate of sildenafil absorption. A faster rate of absorption within the first 5 to 20 minutes post-dose was observed with ASP-001, and Cmax modestly exceeded bioequivalence criteria compared with reference tablets. Bioequivalence was established for the active metabolite piperazine N-desmethyl-sildenafil for both rate and extent of absorption. No oral irritation was reported. Adverse events occurred at similar rates in both treatment periods and treatment groups across test and reference products. The results suggest that the ASP-001 formulation may be a safe and effective alternative to currently marketed products for the treatment of erectile dysfunction.