After intravenous administration of different doses of 131I-labelled aprotinin to healthy volunteers, the activity concentrations in serum and urine were measured over a period of 48 hours.The course of serum concentrations shows an initial steep slope followed by a flattening of the curve. Regarding the region of main interest (1 to 12 hours after injection) the decrease of serum concentration can be fitted by two superimposed exponential terms, exhibiting half-lives of 0.7 and 7 hours. The course of the serum concentration curve within the first 12 hours can be interpreted as the overlapping of different distribution mechanisms: The initial distribution in the extracellular fluid is followed by a slower accumulation in the deep compartments of the kidney and the cartilage tissue.In the urine 25 to 40% of the administered activity are found within 48 hours. The renal excretion rate up to 12 hours after injection is approx. 1% of the dose per hour, and it decreases to approx. 0.5% in the following 36 hours.Since the concentrations in serum are proportional to the given dose, and since the individual deviations of the concentrations related to the dose are relatively small, it is possible, for clinical purposes, to estimate required doses or available concentrations on the basis of the relative serum concentration curve determined experimentally in the present study.

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