Highly sensitive LC-MS/MS methods for the determination of seven human CYP450 activities using small oral doses of probe-drugs in human.

Cocktails composed of several Cytochrome P450 (CYP450)-selective probe drugs have been shown of value to characterize in vivo drug-metabolism activities. Our objective was to develop and validate highly sensitive and selective LC-MS/MS assays allowing the determination of seven major human CYP450 isoenzyme activities following administration of low oral doses of a modified CYP450 probe-drug cocktail in patients. The seven-drug cocktail was composed of caffeine, bupropion, tolbutamide, omeprazole, dextromethorphan, midazolam (all administered concomitantly) and chlorzoxazone (administered separately) to phenotype for CYP1A2, 2B6, 2C9, 2C19, 2D6, 3A4/5 and 2E1, respectively. Serial plasma and urine samples were collected over an 8h period. The probe-drugs and their respective metabolites were measured in both human plasma and urine, except for omeprazole (plasma only) and chlorzoxazone (urine only). Samples were analyzed by high performance liquid chromatography with heated electrospray ionization tandem mass spectrometry (HPLC-HESI-MS/MS) using a Phenomenex Luna PFP (2) analytical column (3μm PFP(2) 150×3mm) for chromatographic separation. Optimal detection was achieved based on 3 different analytical methods; (1) isocratic elution with a mobile phase consisting of acetonitrile and water both fortified with 0.01% formic acid for the analysis of bupropion, tolbutamide, chlorzoxazone and their respective metabolites; (2) isocratic elution with a mobile phase composed of acetonitrile and ammonium formate (pH 3; 10mM) for omeprazole, dextromethorphan, midazolam and their metabolites; (3) for caffeine and paraxanthine, gradient elution using acetonitrile and 0.01% formic acid in water was used. All calibration functions were linear for all probe drugs and metabolites in both matrices over wide analytical ranges. The main advantages of our methods are the use of specific probe drugs available in most countries, the administration of small doses of probe drugs, small volume of plasma required for the analyses and simple and rapid extraction procedures. The methods met all requirements of specificity, sensitivity, linearity, precision and accuracy and stability generally accepted in bioanalytical chemistry. Determination of CYP450 phenotype in patients will permit characterization of their capacities to metabolize drugs through CYP450 under specific conditions at a definite time. This tool will be highly clinically relevant since wide intersubject variability observed in drug response is largely explained by variation in drug metabolism; it will be particularly useful in polymedicated patients with multiple comorbidities. So far, our CYP450 cocktail assays have been successfully applied to phenotype CYP450 activities in patients.