Calibration curves for the three metabolites were run in triplicate over the range of 1000 to 1 pg and are shown in Figures 3 - 5. The original xenobiotics can also be quantified, if desired, to determine percent usage of the drug (data not shown). Excellent linearity is seen within this range with the average correlation coefficient being 0.993. Accuracy in retention times of the metabolites is also excellent with an average 1.15% RSD, the dextrorphan being slightly more variable (2.74% RSD).
With this application note we have demonstrated a single method for the separation and quantification of the enzymatic activities of the three most important Cytochrome P450 enzymes (3A4, 2D6 and 2C9). This method can be used for pre-clinical evaluation of NCEs as inhibitors of CYPs or quantification of these metabolites from clinical samples after SPE.
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