Quantification of sibutramine and its two metabolites in human plasma by LC-ESI-MS/MS and its application in a bioequivalence study

Obesity can be considered as a chronic illness of epidemic proportion and its incidents have increased exponentially in recent years.The use of anti-obesity drugs such as sibutramine is somewhat helpful.There is a need to quantify such drugs in biological samples,which is generally quite difficult.In this report,we developed and validated a simple,sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of sibutramine (SB) and its two metabolites N-des methyl sibutramine (DSB) and N-di desmethyl sibutramine (DDSB) in human plasma.Zorbax SBC18 (4.6 mm × 75 mm,3.5 μm,80 (A)) analytical column and 5 mM ammonium formate:acetonitrile (10∶90,v/v) mobile phase were used for chromatographic separation of SB,DSB and DDSB.Multiple reaction monitoring (MRM) in the positive mode was used to detect SB,DSB and DDSB at m/z 280.3/124.9,266.3/125.3 and 252.2/124.9,respectively.Liquid liquid extraction was used for the extraction of analytes and internal standard from human plasma.This method was validated over a linear concentration range of 10.0-10,000.0 pg/mL for SB,DSB and DDSB with correlation coefficients (r) of ≥0.9997.The drug and the two metabolites were stable in plasma samples.The validated method was successfully applied in a bioequivalence and pharmacokinetic study with human volunteers under fasting condition.