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Diazepam-omeprazole inhibition interaction: an in vitro investigation using human liver microsomes (

Diazepam-omeprazole inhibition interaction: an in vitro investigation using human liver microsomes (

  1. Jatelka
    British Journal of Clinical Pharmacology 1996 Aug;42(2):157-62

    Zomorodi K, Houston JB

    1. The metabolism of diazepam to its primary metabolites 3-hydroxydiazepam (3HDZ) and nordiazepam (NDZ) was evaluated in human liver microsomes. The 3HDZ pathway was the major route of metabolism representing 90% of total metabolism with a Vmax/Km ratio of 0.50-7.26 microliters min-1 mg-1 protein.

    2. Inhibition of the two metabolic pathways of diazepam by omeprazole was investigated. The NDZ pathway was not affected by omeprazole whilst a Ki of 201 +/- 89 microM was obtained for the 3HDZ pathway (Km/Ki ratio of 3.0 +/- 0.9).

    3. Inhibitory effects of omeprazole sulphone on the 3HDZ and NDZ pathways were also investigated. Omeprazole sulphone inhibited both pathways with similar Kis of 121 +/- 45 and 188 +/- 73 microM respectively (Km/Ki ratios of 5.2 +/- 2.3 and 3.3 +/- 1.5 respectively).

    4. These in vitro data provide direct evidence for cytochrome P450 inhibition as the mechanism for the well documented diazepam-omeprazole clinical interaction and indicate that omeprazole sulphone, as well as the parent drug, contribute to the inhibition effect.