[Effect of diazepam and barbiturates on the in vivo metabolism of halothane and enflurane in rats].

The effect of pretreatment with barbiturates or diazepam on the in vivo metabolism of halothane or enflurane (92 ppm) was investigated upon application by inhalation. In male rats exposed to halothane the elimination half-life from the atmosphere of the closed exposure system amounted to 0.64 h; pretreatment with thiopental or methohexital (40 mg/kg i.p.) caused a small, but significant prolongation of the half-life (1.3 or 1.4-fold), whereas hexobarbital (75 or 100 mg/kg i.p.) had no effect in this respect. Much stronger and dose-dependent effects were seen in rats pretreated with pentobarbital (25 or 50 mg/kg i.p.; 2 or 3-fold) or diazepam (5 or 10 mg/kg i.p.; 3 or 5-fold increase). In control rats exposed to enflurane the elimination half-life was 4.77 h; pretreatment with hexobarbital, thiopental or methohexital at the above doses did not alter this value, whereas pentobarbital and diazepam again exerted marked and dose-dependent effects: a 1.5 or 1.7-fold prolongation of the half-life was observed after pentobarbital (25 or 50 mg/kg i.p.) and a 1.9 or 3.3-fold prolongation after diazepam (5 or 10 mg/kg i.p.), respectively. These different effects of the pretreatment drugs seems to correlate with their own pathways and rates of metabolism.