—After parenteral administration of penicillin, up to 70 per cent of the drug is excreted unchanged in the urine. In order to determine the fate of the remainder of the penicillin and the excretion path of penicillin after intramuscular and oral administration, Rowlands and his co-workers182 made urinary excretion studies in female cats, using radioactive penicillin (penicillin containing the radioactive sulfur isotope S35). The radioactivity of the urines was calculated as "Geiger-penicillin units" on the basis that 1,100 disintegrations a minute are equivalent to 1 unit of penicillin. Nonpenicillin radioactivity was calculated by subtracting the biologic penicillin level from the Geiger penicillin level. Results demonstrated that after intramuscular injection of labeled penicillin, 72 to 101 per cent of Geiger penicillin was recovered in the urine and only 36 to 66 per cent of biologic penicillin. The authors state that the difference between
BEERMAN H, NICHOLAS L, BUERK MS, FORD WT. SYPHILIS: A Review of the Recent Literature. Arch Intern Med (Chic). 1950;85(4):699–721. doi:10.1001/archinte.1950.00230100156005
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