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

• Published in: Clinical pharmacology and therapeutics Vol. 52; no. 2; p. 170
• Main Authors: Rost, K L, Brösicke, H, Brockmöller, J, Scheffler, M, Helge, H, Roots, I
• Format: Journal Article
• Language: English
• Published: United States 01.08.1992
• Subjects: Adolescent; Adult; Aged; Aged, 80 and over; Aryl Hydrocarbon Hydroxylases; Breath Tests - methods; Caffeine - analogs & derivatives; Carbon Dioxide - metabolism; Carbon Isotopes; Cytochrome P-450 CYP1A2; Cytochrome P-450 CYP2C19; Cytochrome P-450 Enzyme System - biosynthesis; Cytochrome P-450 Enzyme System - drug effects; Cytochrome P-450 Enzyme System - genetics; Cytochrome P-450 Enzyme System - metabolism; Dose-Response Relationship, Drug; Enzyme Induction; Female; Humans; Male; Mephenytoin - metabolism; Middle Aged; Mixed Function Oxygenases - genetics; Mixed Function Oxygenases - metabolism; Omeprazole - pharmacokinetics; Omeprazole - pharmacology; Oxidoreductases - biosynthesis; Oxidoreductases - drug effects; Oxidoreductases - metabolism; Phenotype
• ISSN: 0009-9236
• DOI: 10.1038/clpt.1992.126

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. The mean percentage exhalation of the 13C test dose, as determined by 13CO2 in breath during 8 hours, was 23.0% +/- 8.0% (n = 18) before treatment. The largest increases in exhalation rate of 13CO2 were observed in the poor metabolizers and the intermediate metabolizers (range, 12.8% to 62.9%; median, 38.9%); median area under the plasma concentration-time curves (AUC) of omeprazole was four times higher than in the extensive metabolizers. The change after omeprazole treatment in extensive metabolizers ranged from -9.8% to +47.7% (median, 12.3%; n = 12) of pretreatment values. In both groups exhalation rates of 13CO2 returned to near pretreatment values within the 7-day washout period (24.2% +/- 7.8%; n = 17). Changes in the 13C-caffeine breath test correlated well with both the pretreatment value (R = -0.67, p = 0.003; n = 18) and the plasma AUC of omeprazole (R = 0.61, p = 0.007; n = 18). Therapeutic doses of omeprazole seem to induce CYP1A2 activity in poor metabolizers, whereas they exert minor inducing effects in extensive metabolizers of S-mephenytoin.