Reversed Phase High Performance Liquid Chromatographic Method for Determination of Sildenafil in Human Plasma and its Application to a Bioequivalence Study

Sildenafil Citrate is a drug used to treat erectile dysfunction and pulmonary arterial hypertension (PAH). A sensitive and specific method based on High Performance Liquid Chromatography (HPLC) was developed and validated for the determination of Sildenafil in human plasma using nabumetone as internal standard. They were extracted from plasma by liquid-liquid extraction and separated isocratically on a C18 μ-Bond pack 5μm, 150 x 3.6 mm, Waters, U.S.A, with as mobile phase of acetonitrile: phosphate buffer 0.05M (55: 45 v/v), pH 4.6. Detection was carried out using UV detector at 295 nm. The chromatographic separation was obtained within 10 min and was linear in the concentration range of 25-1200 ng/mL (r= 0.9992). The method was successfully applied for the bioequivalence study of two tablet formulations of Sildenafil 100 mg after single oral dose administration to 22 healthy human volunteers. Single dose randomized bioequivalence study was done to compare the pharmacokinetic parameters of VIVAG (test, Sildenafil citrate 100mg tablets) versus VIAGRA (references, Sildenafil Citrate 2 X50mg tablets). The 90% confidence intervals were calculated for the Cmax, AUC (0-t) and AUC (0-∞), giving values between 88.55–104.06 % demonstrating the bioequivalence of the two formulations.