[Studies on the metabolic fate of 14C-rokitamycin. II. Accumulation of radioactivity in rats after consecutive oral administration].

After a consecutive oral administration of 200 mg/kg/day of 14C-rokitamycin (TMS-19-Q) daily for 28 days to male rats, the accumulation of radioactivity in tissues and its disappearance after the cessation of the administration was studied. Blood concentrations at peak times and 24 hours after each administration were determined daily. Both values increased gradually until the 14th day and thereafter remained roughly constant. The extent of elimination of radioactivity from the blood was practically not affected by the consecutive administration. Affinities of radioactivity to the liver, kidney, spleen, adrenal, pituitary gland, preputial gland, thyroid, intraorbital lacrimal gland and bone marrow were comparatively higher than those to other tissues. Tissue concentrations in the above mentioned tissues at the 1st day after the completion of consecutive administrations for 14 and 28 days were 2.6-6.1 and 3.2-6.8 times higher, respectively, than those at the 1st day after a single administration. The elimination of radioactivity from the tissue after the consecutive administration for 28 days was slightly slower than that after a single administration. In the consecutive daily administration for 28 days, the metabolic fate of radioactivity reached a steady state after 14 days of consecutive daily administration. Hence, the accumulation of the radioactivity did not particularly occurred. During the consecutive administration, recoveries of radioactivity in the urine and feces were almost at a constant rates, with 8.0 and 93.8% of the total radioactivity given excreted in the urine and feces, respectively, within 10 days after the last administration.