Determination of diethylcarbamazine, an antifilarial drug, in human urine by 1H-NMR spectroscopy.

1H-NMR spectroscopy is a convenient method for determination of diethylcarbamazine (DEC) in urine, and can be used to monitor medication with the drug. Urine samples were mixed with 10% of deuterium oxide as a spectrometer field frequency lock, which is the only sample pretreatment required. Tailored excitation with the 1331 pulse was used for water peak suppression. The quantification of DEC was carried out with the triplet of the N-ethyl group, for which the T1 relaxation time was 1 s. In aqueous solutions, amounts below 1 microgram ml-1 of DEC could be easily detected. In urine, the detectability depended on the level of chemical noise but was better than 10 micrograms ml-1. The accuracy and precision of the method were better than 15%. Analysis of urine from volunteers receiving a single therapeutic dose of DEC (6 mg kg-1 body weight orally) showed that the drug was eliminated in unchanged form during 2 days, in agreement with earlier results. The concentration of DEC in urine several hours after the intake exceeded 100 micrograms ml-1 making the 1H-NMR assay rapid and easy. No significant amounts of the N-oxide of DEC could be detected.