Development and validation of an HPLC-UV method for simultaneous determination of sildenafil and tramadol in biological fluids: Application to drug-drug interaction study.

The introduction of sildenafil (SDF) to treat erectile dysfunction has solved a widespread condition with negative on the quality of life. Recently, the co-administration of tramadol (TMD) with SDF to manage premature ejaculation has illegally increased and thus drug-drug interaction studies of these drugs became of great importance. Although certain biological functions have been altered upon co-administration of the two drugs, methods for their determination in vivo to understand their interactions have yet to be published. Herein, therefore, an HPLC method with photometric detection was developed for the determination of a binary mixture of TMD and SDF in rabbit plasma after oral administration. In this study, a reversed-phase chromatography was performed at room temperature on a C18 column with a mobile phase composed of 10 mM Na2 HPO4 solution (pH 7.5): acetonitrile (45:55, v/v) at a flow rate of 0.8 mL min-1 using caffeine (CAF) as an internal standard. The detector was set at 220 nm. The total analysis time was 6 min. Calibration graphs were linear in the concentration ranges of 0.1-10 and 0.05-10 μg mL-1 with a detection limit of 0.05 and 0.02 μg mL-1 for TMD and SDF, respectively. The method was validated in terms of accuracy, precision, limit of detection and quantitation, recovery, and stability as per US FDA bioanalytical guidelines. In addition, the metabolites N-desmethylsildenafil (UK-103,320) and O-desmethyltramadol were quantified in rabbit plasma after 2 h of oral administration using LC-MS/MS. The simultaneous administration of TMD with SDF has affected peak plasma concentration (Cmax ), Tmax , area under the concentration-time curve (AUC), and the elimination rate constant (Kel ) of SDF. The present study is the first to give valuable insights into the drug-drug interaction and the pharmacokinetic implications associated with the co-administration of SDF and TMD.