DISTRIBUTION AND EXCRETION OF RADIOACTIVITY IN RATS RECEIVING N-METHYL-C¹⁴-ERYTHROMYCIN

¹ The Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana

The general pattern of erythromycin distribution and excretion was studied in 10 rats after intravenous administration of N-methyl-C¹⁴-erythromycin.

Erythromycin was rapidly metabolized in the liver, mainly through demethylation process, and excreted in the bile as des-N-methyl-erythromycin. The isotopic methyl group was eliminated in the expired air as C¹⁴O₂.

Erythromycin and its metabolites quickly got into the intestinal tract, chiefly by way of bile and in part by direct passage through the intestinal wall.

At the end of 20 hours after administration of isotopic erythromycin in rats, about 37-43 per cent of the injected radioactivity was recovered in the intestinal tract plus feces; 27-36 per cent in the urine; and 21-29 per cent in the expired air.

There was a general distribution of radioactivity in various tissues of rats following isotopic erythromycin administration. Concentrations of radioactivity were found to be high in the liver, spleen, pancreas, kidney, adrenals, submaxillary glands and lungs in addition to urine, bile, feces and intestinal tract; low in skin, fat and brain; and intermediate in other tissues.

Intracellular distribution studies indicated that erythromycin and its metabolites were capable of entering various cellular components of the liver.