Abstract
Time courses of concentrations of 3H-fentanyl in plasma and several organs and tissues after i.v. injection as well as the quantitative role of metabolism and excretion were studied in rabbits. A simple method for measuring 3H-fentanyl concentration in plasma separated from its radioactive metabolites is described. The time course of concentration in plasma could be divided into three phases, each one being governed by one of the following factors: distribution and redistribution in the organism, metabolism or excretion. In the first phase, lasting about 10 minutes after injection where mainly distribution phenomena were found, a considerable difference in concentration between arterial and venous plasma was observed. The concentrations of fentanyl in the organs were much higher than in plasma, the lungs reaching 100 times the plasma concentration. It is pointed out that the end of the pharmacologic effect at less than 30 minutes after i.v. injection lies in the second kinetic phase. Until that time redistribution and metabolism are both important for the decrease of brain concentration. The relation between time course of brain concentration and pharmacologic effect is discussed.
Footnotes
- Received December 28, 1970.
- Accepted September 8, 1971.
- © 1971 by The Willams & Wilkins Co.
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