Simultaneous determination and pharmacokinetic study of metformin and pioglitazone in dog plasma by LC-MS-MS.

A high-performance liquid chromatography-tandem mass spectrometry method was developed for the simultaneous determination of metformin (MET) and pioglitazone (PIO) in dogs. To increase the reliability of the method, moroxydine (IS-1) and rosiglitazone (IS-2) were used as internal standards for MET and PIO, respectively. The analytes were extracted from beagle dog plasma by a one-step protein precipitation. Chromatographic separation was performed on a Phenomenex Synergi POLAR-RP 80A column (250 × 4.6 mm, 4 µm). The total chromatographic run time was 8.0 min, with retention times of 3.0 and 2.9 min for MET and IS-1, respectively, and 6.1 and 4.9 min for PIO and IS-2. The lower limit of quantitation values were 2 and 1 ng/mL for MET and PIO, respectively. The recoveries ranged from 96.4 to 112.8% for MET and 102.1 to 104.5% for PIO.