THE RENAL CLEARANCE AND PLASMA PROTEIN BINDING OF AUREOMYCIN IN MAN

¹ Medical Services,the Cardiovascular Research Group and the Department of Laboratories, Mount Sinai Hospital, N. Y.
² Second Medical Services, Mt. Sinai Hospital, N. Y.

1. Simultaneous renal clearance determinations of aureomycin, endogenous creatinine and/or inulin were performed in a total of sixteen human subjects receiving the antibiotic either orally or intravenously. The results indicate that aureomycin is cleared at about 35 per cent of the glomerular filtration rate.

2. Variations of urine flow from 0.1 to 11.0 ml. per mm., and of plasma aureomycin concentrations from 1 to 18 microgm. per ml., and the production of osmotic diuresis with hypertonic mannitol all failed to influence significantly the aureomycin/inulin clearance ratio. This is strong evidence in favor of the absence of renal tubular participation in the excretion of aureomycin.

3. Analyses of ultrafiltrates from aureomycin-containing human plasma and salt-poor human albumin solutions indicate that in the concentration usually employed about 70 per cent of the aureomycin is bound to plasma components and that of the total amount bound, approximately 85 per cent is albuminbound.

4. The renal clearance of free (filterable) aureomycin closely approximated the glomerular filtration rate (simultaneous inulin clearance) in three subjects so studied.

5. The renal excretion of aureomycin is solely a process of glomerular filtration tion of the free (filterable) component. The antibiotic is neither reabsorbed nor secreted by the tubule cells. Its final concentration in the urine merely reflects the tubular reabsorption of water. As the free (therapeutically active) component of the drug is dissipated by excretion and metabolism, more of it is liberated from the protein-aureomycin complex. It is these characteristics which explain the prolonged therapeutic blood levels and relatively high urine concentrations obtained following a given dose of the drug.

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