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The influence of rifampin treatment on caffeine clearance in healthy man.
J Hepatol
January 1995
Department of Internal Medicine, Technical University, Aachen, Germany.
Background/aims: Since cytochrome P450IA2 is involved in the metabolism of procarcinogens and carcinogens, there is debate about whether induction of this enzyme system by pharmaceuticals leads to a higher risk of malignancy. We investigated rifampin as a potent inducer of the hepatic mixed function oxygenase system and its effect on caffeine metabolism which can be taken as an in vivo marker of cytochrome P450IA2 activity.
Methods: Caffeine clearance was measured in ten healthy volunteers before and after a 7-day treatment with 600 mg rifampin.
Omeprazole does not enhance the metabolism of phenacetin, a marker of CYP1A2 activity, in healthy volunteers.
Ther Drug Monit
June 1994
Department of Pharmacology and Therapeutics, University of Pavia, Italy.
Omeprazole has been reported to increase cytochrome P450IA2 (CYP1A2) activity in vitro, but whether this effect also occurs in vivo is controversial. To clarify this issue, the effect of omeprazole (20 mg/day for 8 days) on the kinetics and metabolism of phenacetin, an in vivo marker of CYP1A2 activity, was examined in 10 healthy volunteers. The pharmacokinetic parameters of phenacetin and metabolically derived paracetamol on the 8th day of omeprazole administration were very similar to those observed in a control session in the absence of omeprazole administration, the only significant difference being a higher peak plasma phenacetin concentration during omeprazole treatment.
View Article and Find Full Text PDFOmeprazole induction of cytochrome P-450IA2: the importance of selecting the appropriate human model.
Hepatology
April 1993
Clinical Research Center, University of Michigan Medical School, Ann Arbor 48105.
Increase of cytochrome P450IA2 activity by omeprazole: evidence by the 13C-[N-3-methyl]-caffeine breath test in poor and extensive metabolizers of S-mephenytoin.
Clin Pharmacol Ther
August 1992
Institute of Clinical Pharmacology, Klinikum Steglitz, Free University of Berlin, Germany.
Omeprazole has been shown to induce cytochrome P450IA1 and P450IA2 activity in vitro. To reflect cytochrome P450IA2 (CYP1A2) activity in vivo, the 13C-[N-3-methyl]-caffeine breath test was conducted in 18 volunteers: 12 extensive metabolizers, one intermediate metabolizer, and five poor metabolizers of S-mephenytoin. Breath tests were performed before treatment with an oral dose of 40 mg omeprazole, on the seventh day of treatment, and after a 7-day washout period.
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