High-performance liquid chromatographic determination of 6,8-difluoro-1-(2-fluoroethyl)-1,4- dihydro-7-(4-methyl-1-piperazinyl)-4-oxo-3-quinolinecarboxylic acid and its metabolites in laboratory animals.

A simple, sensitive and specific high-performance liquid chromatographic method for a new quinolone antimicrobial agent, 6,8-difluoro-1-(2-fluoroethyl)-1,4- dihydro-7-(4-methyl-1-piperazinyl)-4-oxo-3-quinolinecarboxylic acid (AM-833, I), and its metabolites in serum and urine has been developed for their simultaneous determination. This method is based on ion-pair extraction and separation by ion-pair reversed-phase chromatography with ultraviolet or fluorescence detection. The major metabolites in the serum and urine of mice, rats, dogs and monkeys were N-desmethyl I (compound II) and I N-oxide (compound III). Rabbit serum and urine contained N-desmethyl-3-oxo I (compound IV), 3-oxo I (compound V) and N-desmethyl-4-formyl I (compound VI) in addition to compounds I, II and III. Unchanged drug accounted for 80-90% of total serum concentrations in mice and more than 90% in rats, dogs and monkeys up to 6 h after dosing, whereas the fraction of compound I in rabbits was 34-67%. Unchanged drug was the most predominant in the urine of mice, rats, dogs and monkeys, whereas compound II was the most abundant in rabbit urine. Although rabbits and monkeys excreted 70-80% of dose in three-day urine, the total urinary excretion of mice, rats and dogs was relatively low, 40-50% of oral dose. The fraction of compound I in total urinary excretion was 63, 73, 27, 55 and 78% in mice, rats, rabbits, dogs and monkeys, respectively. These results suggest that there is a species difference in the metabolism and excretion pathway of compound I.