Rapid and Sensitive Determination of Udenafil in Plasma by LC-MS/MS for Intranasal Pharmacokinetic Study in Rats

A rapid and sensitive analytical method for udenafil in rat plasma was developed and validated using liquid chromatography-tandem mass spectrometry (LC-MS/MS). This chromatographic procedure was then applied to the in viva pharmacokinetic studies in rats for determining the advantages of intranasal administration of the drug over oral administration. Using liquid liquid extraction (LLE), udenafil and the internal standard (IS) sildenafil were extracted with dichloromethane from 100 mu l of plasma samples. Chromatographic separation was performed using Pursuit XRS C-18 column (50 mm x2.1 mm, i.d., 3 mu m, Varian Inc., CA, U.S.A.) with an isocratic mobile phase consisting of acetonitrile and 10 mm ammonium acetate (90: 10, v/v) at a flow rate of 0.2 ml/min over a total run time of 2.5 min. Detection and quantification was performed by mass spectrometry using the multiple reaction-monitoring mode at m/z 517.4 -> 283.1 for udenafil and m/z 475.3 -> 4100.0 for IS. Results showed that the developed method was sensitive and specific for udenafil. Linearity was obtained in the range of 0.5-1000 ng/ml. The coefficient of variation of both intra- and inter-day validation were below 11.6% and the intra- and inter-day accuracy ranged from 91.5 to 109.9%. Udenatil concentration was successfully measured from plasma after intranasal as well as after intravenous or oral administration at clinical dose (1.67 mg/kg) in rats. Moreover, the T-max values obtained from pharmacokinetic studies suggested that administration of udenafil intranasally could be more effective than by the oral route.