The pharmacokinetics of a single dose of netilmicin (NM) was studied in 6 healthy volunteers. Elimination of the drug was followed in serum and urine for 24 h and 72 h, respectively. NM concentrations were measured with a modified radioenzymatic assay. A three compartment open model was employed to calculate the pharmacokinetic parameters. Following the rapid initial distribution, biphasic elimination with half lives of 1.99 (t 1/2 beta) and 36.89 h (t 1/2 gamma) was demonstrated. Measurable amounts of NM were excreted in the urine for up to 72 h. The volume of distribution at steady-state (Vdss) of 0.68 l/kg was 3 to 4 times larger than previously reported for this antibiotic. NM plasma clearance was 91 ml/min and the renal clearance was 67 ml/min. The data indicate that on repetitive dosing the amount of drug in the body would be considerably underestimated if the prolonged terminal elimination phase were not taken into account. During prolonged treatment, accumulation of NM in renal and other tissues is likely to occur, as has been described for other aminoglycosides. The possible consequences of this pharmacokinetic behaviour are discussed.

Supported in part by Schweiierischer Nationalfonds zur Forderung der wissenschaftlichen Forschung.t QEZ = (7-Chlor-3-ethyl-1,2,3,4-tetrahydro-4-oxo-6-sulfamyl-) quinazoline (Lederle Laboratories Division, New York, N. Y.). 47 1

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Kinetic analysis of minocycline concentrations in plasma and urine resulted in the following findings: In normal subjects the biological half-life is about 17 hours after the first dose and 21 hours after repeated administration. The renal drug clearance is only about 8% of the overall plasma clearance which is independent of renal function with a mean value of 47 ml/min. The fraction of the absorbed dose eliminated unchanged in the urine is only 9--19%. As a consequence the elimination rate of the drug is practically independent of renal function and decreases only 9--19% in anuric patients. The renal drug clearance depends linearly on renal function. The gastro-intestinal bio-availability of minocycline from the coated tablet preparation is incomplete. The cumulative behaviour of the drug corresponds to the kinetic parameters determined after repeated administration. It is suggested that the usual dosage regimen should be used in patients with renal disease.

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