The absorption, distribution, and excretion of 14C-penicillic acid by rats.

Adult male and female rats were given 14C-penicillic acid (labeled in the 1, 3, and 5 positions by fermentation with acetate-1-14C) by oral intubation and were sacrificed at 1, 2, 4, 24, 48, 72, and 168 hours following administration of the labeled compound. Approximately 98 p. 100 of the 14C-radioactivity given was absorbed from the gastrointestinal tract of the rats during the first 48 hours. After 7 days, 82 p. 100 was recovered in the urine and 13 p. 100 in the feces. Less than 1 p. 100 of the total radioactivity was recovered as 14CO2 from the expired air; most of this amount was recovered within the first 72 hours after administration. Various tissues were, analyzed for 14C-radioactivity throughout the 7-day-period; no significant retention of radioactivity was apparent in any of the tissues examined. The level of 14C-penicillic acid reached a maximum in the blood and tissues 2-4 hours after administration. Red blood cells contained the highest concentration of 14C-radioactivity. Liver, bladder, kidneys, heart, and bile also showed a high level of 14C-radioactivity concentration. The estimated biological half-life of penicillic acid was 18.7 and 17.1 hours for the male and female, respectively. The estimated biological half-retention time from the point of administration by the red blood cells, liver, and kidney of the male and female rats was 24.2 and 14.0; 19.8 and 17.8; and 21.3 and 19.0 hours, respectively. Recovery studies indicated no unchanged penicillic acid in the urine.