Effect of doxapram on the action of other drugs and the hepatic drug-metabolizing system in mice.

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Abstract
Effects of doxapram, a respiratory stimulant, on the action of other drugs and the activity of the hepatic drug-metabolizing enzyme were studied in mice. The hypothermic effect induced by aminopyrine and the muscle relaxant effect induced by meprobamate were potentiated by the pretreatment with doxapram 60 min before. Doxapram significantly enhanced the lethalities of picrotoxin and strychnine, and the analgesic actions of aminopyrine and morphine. The plasma concentration of aminopyrine or pentobarbital in doxapram-treated mice was higher than those in untreated mice, and the plasma concentration of nor-nitrogen mustard related to an active metabolite of cyclophosphamide after the administration of cyclophosphamide was lower in doxapram-treated mice. Doxapram (50 mg/kg, i.p.) reduced remarkably the activities of aminopyrine N-demethylase and aniline hydroxylase in the hepatic 9000 .times. g supernatant fraction, and reduced the cytochrome P-450 contents in hepatic microsomes. No significant alteration by doxapram was observed on the activities of NADH-ferricyanide reductase and NADPH-cytochrome c reductase and cytochrome b5 contents. The mechanisms of the interaction between doxapram and combined drugs may have involved the depression of the hepatic drug-metabolizing system in microsomes, and a subsequent variation of drug level in the plasma.