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Abstract
1. After intramuscular injection of a new semi-synthetic penicillin, disodium [14C]α-sulphobenzylpenicillin, to rats radioactivity in blood reached a peak at 5 min with a half life of 26 min. Most of the blood radioactivity was not bound to plasma protein and 70% was accounted for as the intact penicillin.
2. At 20 min after dosage the radioactivity was distributed mostly in liver, kidney, intestinal contents and blood. About half of the injected radioactivity was excreted into the urine within 8 h. Faecal excretion was much slower but continued for longer duration and amounted to 24% after 3 days.
3. In bile-duct cannulated rats, 35% of the dosed radioactivity was excreted into bile and 52% into urine within 24 h.
4. In both urine and bile, 50 to 85% of the radioactivity was present as unchanged drug and 10 to 20% as its penicilloic acid.
5. Intravenous injection gave similar metabolic patterns as those observed after intramuscular injection except that faecal excretion was increased.
6. Autoradiographic studies on mice were similar to findings on the tissue distribution study for the rat.