Blood samples were drawn immediately before taking the drug (control), at 20, 40 minutes, and 1, 1.5, 2, 2.5, 3, 4, 6, 9, 12, 24, 36 hours after drug administration. Seven days after the first drug administration (washout period), the procedure was repeated using the alternate drug. The plasma concentrations of pregabalin were determined by using validated liquid chromatography with tandem mass spectrometry detection (LC-MS/MS) method.