Doxapram metabolism in human fetal hepatic organ culture

The biotransformation of doxapram, a respiratory stimulant was studied with use of explants from human fetal livers (n = 15 fetuses) obtained from therapeutic abortions (gestational age, 10 to 20 weeks). Explants were cultured in Leibowitz medium and the media from cultured samples were collected before and at 3, 6, 12, and 24 hours after incubation with 2.5, 5.0, and 10 micrograms/ml doxapram. The concentrations of doxapram and its metabolites (AHR 0914, an analog of doxapram, AHR 5955 or ketodoxapram, and AHR 5904) were measured by high pressure liquid chromatography. Explant histopathology and alkaline phosphatase activity showed no direct toxic effects of the drug on liver tissue. The fastest rate of doxapram metabolism occurred during the first 3 hours of incubation (198 +/- 73.3, 438 +/- 63.3, and 538 +/- 62 ng/mg/hr liver protein at doxapram concentrations of 2.5, 5.0, and 10.0 micrograms/ml, respectively). At 3 hours of incubation, the amount of doxapram metabolized (nanogram per milligram of liver protein) was significantly higher (p less than 0.01) at doxapram concentrations of 10.0 (1616 +/- 186) and 5.0 microgram/ml (1315 +/- 190) than at 2.5 micrograms/ml (594 +/- 220). The oxidative pathway producing keto-doxapram, or AHR 5955 and AHR 5904, is more active than the de-ethylation producing the analog of doxapram AHR 0914. Data indicate substantial metabolism of doxapram by the human fetal lives.