| Abstract: | The effects of the volatile anesthetics, enflurane, isoflurane and halothane, on the pharmacokinetics of antipyrine were examined in mice. The administration of 0.75% isoflurane or 1.0% enflurane in air resulted in a 173 and a 206% increase, respectively, in antipyrine plasma half-life and a 29.1 and a 41.2% decrease in antipyrine total body clearance. There was also an almost 2-fold increase in the volume of distribution of antipyrine. Halothane, at 0.5% in air, had no significant effect upon antipyrine plasma half-life or its volume of distribution. There was no significant change in antipyrine total body clearance and volume of distribution 4 hr after exposure to the volatile agents, but there was a small increase in half-life. The exposures to the volatile anesthetics were also carried out in an atmosphere of 8% oxygen. Antipyrine plasma half-life was increased significantly by 48% in mice breathing 8% oxygen, compared to mice breathing air. Isoflurane in 8% oxygen increased the plasma half-life of antipyrine by 296% compared to mice breathing 8% oxygen. This increase was greater than the effect of isoflurane seen in mice breathing air. Mice breathing halothane in 8% oxygen exhibited a 21% increase in antipyrine plasma half-life and mice breathing enflurane in 8% oxygen, a 117% increase in antipyrine plasma half-life, although the changes were not markedly different from those seen in mice breathing air. Enflurane and isoflurane produced a significant increase in the volume of distribution for antipyrine in the mice breathing 8% oxygen. Total body clearance of antipyrine was decreased markedly in mice breathing isoflurane and enflurane but showed a lesser decrease in mice breathing halothane in 8% oxygen. In vitro in mouse microsomes, halothane, enflurane and isoflurane were all inhibitors of aminopyrine metabolism. Possible mechanisms for these results are discussed. |
