Mass balance and metabolism studies using radiolabeled substances are well recognized as an important part of the drug development process. Herein, we directly assessed the use of 19F NMR to achieve quantitative mass balance, metabolism and distribution information for fluorinated compounds without the need for radiolabeled synthesis/study. As a test case, the disposition of pefloxacin, a fluoroquinolone antibiotic, was evaluated in rats using quantitative 19F NMR in parallel with a radiolabeled study. Urine, bile, and feces samples were collected over specific periods following oral administration of either 25 mg/kg [14C]pefloxacin or 25 mg/kg pefloxacin and were subsequently profiled by radioactivity or 19F NMR, respectively. The percent dose excreted in each matrix was comparable between the two methods, with total dose recovered by radioactivity and 19F NMR determined to be 86.8% and 81.8%, respectively. In addition, plasma samples were collected to determine the exposure of pefloxacin and its circulating metabolites. The plasma exposure of pefloxacin determined by 19F NMR was within 5% to that calculated by a validated LC-MS/MS bioanalytical method. By both methods, pefloxacin was identified as the major circulating entity with pefloxacin glucuronide as the major circulating metabolite. Quantitative analysis of metabolites in excreta was generally comparable between the two methods. In selected tissues, both methods indicated that parent drug accounted for the majority of the drug-related material. In summary, we have demonstrated that 19F NMR can be used as an alternate method to conventional radiolabeled studies for compounds containing fluorine without the need for radiolabeled synthesis/study.
- biliary excretion
- mass spectrometry/MS
- metabolite disposition
- metabolite identification
- The American Society for Pharmacology and Experimental Therapeutics