Simultaneous determination of carisoprodol and aspirin in human plasma using liquid chromatography-tandem mass spectrometry in polarity switch mode: application to a human pharmacokinetic study.

A simple, sensitive and rapid LC-MS/MS-ESI method has been developed and validated for simultaneous quantification of the carisoprodol and aspirin in human plasma. Carisoprodol was detected in positive ion mode, whereas aspirin was detected in negative ion mode. Carbamazepine and furosemide were used as internal standards (IS) for quantification of carisoprodol and aspirin, respectively. The extraction procedure involves a liquid-liquid extraction method with ter-butyl methyl ether. Chromatographic separation was achieved on a Zorbax XDB-Phenyl (4.6 × 75 mm, 3.5 µm) column using an isocratic mobile phase (5 mm ammonium acetate:methanol, 20:80, v/v) at a flow rate of 0.8 mL/min with a total run time of 2.2 min. A detailed method validation was performed as per the FDA guidelines. The standard curves found to be linear in the range of 25.5-4900 and 15.3-3000 ng/mL for carisoprodol and aspirin, respectively. The results met the acceptance criteria. Carisoprodol and aspirin were found to be stable in various stability studies. The validated method was successfully applied to a pharmacokinetic study following co-administration of carisoprodol (250 mg) and aspirin (75 mg) tablets by oral route to human volunteers.

A rapid and sensitive liquid chromatography-tandem mass spectrometric assay for duloxetine in human plasma: Its pharmacokinetic application.

This paper describes a simple, rapid and sensitive liquid chromatography-tandem mass spectrometry assay for the determination of duloxetine in human plasma. A duloxetine stable labeled isotope (duloxetine d5) was used as an internal standard. Analyte and the internal standard were extracted from 100 µL of human plasma via solid phase extraction technique using Oasis HLB cartridges. The chromatographic separation was achieved on a C18 column by using a mixture of acetonitrile-5 mM ammonium acetate buffer (83:17, v/v) as the mobile phase at a flow rate of 0.9 mL/min. The calibration curve obtained was linear (r2≥0.99) over the concentration range of 0.05-101 ng/mL. Multiple-reaction monitoring mode (MRM) was used for quantification of ion transitions at m/z 298.3/154.1 and 303.3/159.1 for the drug and the internal standard, respectively. Method validation was performed as per FDA guidelines and the results met the acceptance criteria. A run time of 2.5 min for each sample made it possible to analyze more than 300 plasma samples per day. The proposed method was found to be applicable to clinical studies.