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In vitro interaction of the antipsychotic agent olanzapine with human cytochromes P450 CYP2C9, CYP2C19, CYP2D6 and CYP3A
Author(s) -
RING BARBARA J.,
BINKLEY SHELLY N.,
VANDENBRANDEN MARK,
WRIGHTON STEVEN A.
Publication year - 1996
Publication title -
british journal of clinical pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.216
H-Index - 146
eISSN - 1365-2125
pISSN - 0306-5251
DOI - 10.1111/j.1365-2125.1996.tb00180.x
Subject(s) - tolbutamide , olanzapine , clozapine , chemistry , pharmacology , non competitive inhibition , cyp2c9 , cyp3a , cyp2d6 , cyp2c19 , metabolism , cytochrome p450 , biochemistry , endocrinology , biology , medicine , enzyme , schizophrenia (object oriented programming) , diabetes mellitus , psychiatry
1 The ability of olanzapine to inhibit the metabolism of marker catalytic activities for the cytochromes P450 CYP3A, CYP2D6, CYP2C9, and CYP2C19 was examined. This inhibitory capability was compared with that obtained with clozapine and known inhibitory compounds for the same cytochromes P450. 2 Olanzapine, clozapine, and ketoconazole were all found to non‐competitively inhibit 1′‐hydroxy midazolam formation, form selective for CYP3A, yielding K i , values of 491, 99 and 0.11 μM, respectively. The 1′‐hydroxylation of bufuralol, form selective for CYP2D6, was competitively inhibited by olanzapine ( K i = 89μM), clozapine ( K i = 19 μM), and quinidine ( K i = 0.03 μM). Tolbutamide metabolism to 4–hydroxy tolbutamide, form selective for CYP2C9, was competitively inhibited by clozapine and phenytoin ( K i of 31 μM and 17 μM, respectively). Olanzapine non‐competitively inhibited tolbutamide metabolism with a K i of 715 μM. The marker catalytic activity for CYP2C19 mediated metabolism, 4′‐hydroxy S‐mephenytoin formation, was competitively inhibited by clozapine ( K i = 69 μM) and omeprazole ( K i = 4.1 μM). Non‐competitive inhibition of CYP2C19 mediated metabolism was seen with olanzapine with a K i of 920 μM. 3 The calculated percent inhibition by olanzapine of substrates metabolized by CYP3A, CYP2D6, CYP2C9, and CYP2C19 was modeled assuming a total plasma concentration in the therapeutic range (0.2 μM). Total olanzapine vs unbound olanzapine was used to model the worst case (most conservative) situation. In all cases, the calculated percent inhibition of these cytochromes P450 by olanzapine was <0.3%, suggesting that there would be little in vivo inhibition of the metabolism of substrates of these enzymes when co‐administered with olanzapine.