Comparison between Radioanalysis and 19F Nuclear Magnetic Resonance Spectroscopy in the Determination of Mass Balance, Metabolism, and Distribution of Pefloxacin.

Mass balance and metabolism studies using radiolabeled substances are well recognized as an important part of the drug development process. In this study, we directly assessed the use of fluorine nuclear magnetic resonance (19F NMR) to achieve quantitative mass balance, metabolism, and distribution information for fluorinated compounds, without the need for radiolabeled synthesis or 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 after 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 percentage of dose excreted in each matrix was comparable between the two methods, with the 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 liquid chromatography-tandem mass spectrometry 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 the parent drug accounted for most of the drug-related material. In summary, we have demonstrated that 19F NMR can be used as an alternative method to conventional radiolabeled studies for compounds containing fluorine without the need for radiolabeled synthesis/study.

Synthesis of C-14 radiolabeled glucagon receptor antagonist and its use in a human mass balance study.

The synthesis of the radiolabeled glucagon receptor antagonist 1-[14 C] was accomplished based on decarboxylative iodination of acid 2 followed by "reattachment" of 14 C carboxylic function. The method allowed a significant reduction in the number of steps in preparation of the radiolabeled compound. Iodide 4, obtained by the halodecarboxylation, was converted to cyanide 5-[14 C], which was hydrolyzed to provide the radiolabeled acid 2-[14 C]. Coupling with ß-alanine fragment and hydrolysis of ester 6-[14 C] completed the synthesis of the target molecule 1-[14 C]. The resulting compound was utilized in a mass balance and metabolism study where hepatic oxidation followed by a trace amount of sulfate conjugation and elimination was the main clearance pathway for 1 in humans.

Identification and Mitigation of Reactive Metabolites of 2-Aminoimidazole-Containing Microsomal Prostaglandin E Synthase-1 Inhibitors Terminated Due to Clinical Drug-Induced Liver Injury.

Two 2-aminoimidazole-based inhibitors, LY3031207 (1) and LY3023703 (2), of the microsomal prostaglandin E synthase-1 (mPGES-1) enzyme were found to cause drug-induced liver injury (DILI) in humans. We studied imidazole ring substitutions to successfully mitigate reactive metabolite (RM) formation. These studies support the conclusion that RM formation may play a role in the observations of DILI and the consideration of 2-aminoimidazoles as structure alerts, due to the high likelihood of bioactivation to generate RMs.

Identification, synthesis and pharmacological activity of moxonidine metabolites.

The metabolism of moxonidine, 4-chloro-N-(4,5-dihydro-1H-imidazol-2-yl)-6-methoxy-2-methyl-5-pyrimidinamine, LY326869, in rats, mice, dogs, and humans has been examined. At least 17 metabolites were identified or tentatively identified in the different species by HPLC, LC/MS and LC/MS/MS. The identities of seven of the major metabolites have been verified by independent synthesis. The metabolites are generally derived from oxidation and conjugation pathways. Oxidation occurred at the imidazolidine ring as well as the methyl at the 2 position of the pyrimidine ring. All seven metabolites were examined in the spontaneously hypertensive rats (3 mg kg(-1), i.v.) for pressure and heart rate. Only one, 2-hydroxymethyl-4-chloro-5-(imidazolidin-2-ylidenimino)-6-methoxypyrimidine, exerted a short-lasting decrease in blood pressure, albeit attenuated in magnitude compared to moxonidine.