Quantitative dynamic nuclear polarization-NMR on blood plasma for assays of drug metabolism

Analytical platforms for the fast detection, identification and quantification of circulating drugs with a narrow therapeutic range are vital in clinical pharmacology. As a result of low drug concentrations, analytical tools need to provide high sensitivity and specificity. Dynamic nuclear polarization‐NMR (DNP‐NMR) in the form of the hyperpolarization–dissolution method should afford the sensitivity and spectral resolution for the direct detection and quantification of numerous isotopically labeled circulating drugs and their metabolites in single liquid‐state NMR transients. This study explores the capability of quantitative in vitro DNP‐NMR to assay drug metabolites in blood plasma. The lower limit of detection for the anti‐epileptic drug 13C‐carbamazepine and its pharmacologically active metabolite 13C‐carbamazepine‐10,11‐epoxide is 0.08 µg/mL in rabbit blood plasma analyzed by single‐scan 13C DNP‐NMR. An internal standard is used for the accurate quantification of drug and metabolite. Comparison of quantitative DNP‐NMR data with an established analytical method (liquid chromatography‐mass spectrometry) yields a Pearson correlation coefficient r of 0.99. Notably, all DNP‐NMR determinations were performed without analyte derivatization or sample purification other than plasma protein precipitation. Quantitative DNP‐NMR is an emerging methodology which requires little sample preparation and yields quantitative data with high sensitivity for therapeutic drug monitoring. Copyright © 2010 John Wiley & Sons, Ltd. This study demonstrates that quantitative in vitro dynamic nuclear polarization‐NMR (DNP‐NMR) provides high sensitivity and accuracy for the assay of circulating drugs and their metabolites. The lower limit of detection for 13C‐carbamazepine and its metabolite 13C‐carbamazepine‐10,11‐epoxide is 0.08µg/mL in rabbit blood plasma analyzed by single‐scan 13C DNP‐NMR.