THE TISSUE DISTRIBUTION, METABOLISM AND EXCRETION OF LIDOCAINE IN RATS, GUINEA PIGS, DOGS AND MAN

Tissue distribution and urinary excretion of 3 H-lidocaine and its metabolites were determined after p.o. and i.v. treatment of female rats. Excepting the intestine, maximal tissue levels of radioactivity were reached within 30 minutes after both p.o. and i.v. administration. Intestinal radioactivity reached a peak between two and four hours after each treatment, but negligible amounts of radioactivity were found in the feces. These data and the fact that 30% of administered radioactivity was found in 24-hour rat bile pointed to biliary recycling of one or more lidocaine metabolites. The recovery of radioactivity in 24-hour urine was found to be 73% and 65% after p.o. and i.v. treatment in rats, 93% after p.o. administration in guinea pigs and 67% and 76% after p.o. and i.v. treatment in dogs. The major metabolites of lidocaine were identified and quantitated in the 24-hour urine of rats, dogs, guinea pigs and man. In man, 4-hydroxy-2,6-dimethylaniline accounted for 72.6% of dose. This compound was also the major metabolite in dogs (35.2%) and appeared in significant amounts in the urine of rats (12.4%) and guinea pigs (16.4%). Dogs also excreted relatively large amounts of glycinexylidide (12.6%). The major metabolites in rat urine were 3-hydroxylidocaine (31.2%) and 3-hydroxymonoethylglycinexylidide (36.9%), which were also in the bile. Monoethylglycinexylidide (14.9%) and 2,6-xylidine (16.2%) were found in guinea-pig urine.