Glucuronidation of Propofol in Microsomal Fractions from Various Tissues and Species Including Humans

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Abstract
This in vitro study was conducted to evaluate propofol glucuronidation and the effect of concomitantly administered drugs in various species.Propofol glucuronidation was studied in microsomal fractions from rat, rabbit, and human livers. Extrahepatic metabolism was investigated using lung and kidney microsomes. The propofol-uridine diphosphate-glucuronosyltransferase (UGT) activity measured in liver microsomes was higher in rabbit than in rat. Among the three tested species, human livers exhibited the highest activity, with only small variability in the three samples studied. Animal kidney, but not lung (animal or human), microsomes were able to glucuronidate propofol, meaning that extrahepatic metabolism of propofol exists, at least in the kidney, in the tested species (rat and rabbit). Since metabolic interactions are potential sources of prolonged drug effect or overdose, we screened the effect of 21 compounds (known substrates of various UGT or potentially coadministered drugs) on the glucuronidation of propofol by human liver microsomes. Inhibitions obtained with chemicals or drugs glucuronidated by either UGT1 or UGT2 families (1-naphtol, 4-hydroxybiphenyl, carvacrol, n-propylgallate, ketoprofen, chloramphenicol, acetylsalicylic acid) indicated that at least two UGT isoforms are involved in propofol glucuronidation. Inhibition was observed with several drugs potentially coadministered during pre-, per-, or postoperative periods (e.g., acetylsalicylic acid, ketoprofen, oxazepam, fentanyl). Although not directly transposable to the in vivo situation, these results indicate that such interactions are theoretically possible. Similarly, the inhibitory effect of fentanyl on propofol glucuronidation demonstrated by our in vitro study could explain the in vivo drug-drug interaction that has been described for this drug. Nine other widely used drugs had no effect on in vitro propofol glucuronidation. (Anesth Analg 1995;81:855-61)