Assessment of inhibition of bovine hepatic cytochrome P450 by 43 commercial bovine medicines using a combination of in vitro assays and pharmacokinetic data from literature.

BACKGROUND There have been lack of information of inhibition of bovine medicines on bovine hepatic CYP450 at their commercial doses and dosing routes. OBJECTIVE This work was to assess inhibition of 43 bovine medicines on bovine hepatic CYP450 using a combination of in vitro assay and Cmax values from pharmacokinetic studies with their commercial doses and dosing routes in literature. METHOD Those drugs were first evaluated through a single point inhibitory assay at 3 μM in bovine liver microsomes for six specific CYP450 metabolisms, phenacetin o-deethylation, coumarin 7-hydroxylation, tolbutamide 4-hydroxylation, bufuralol 1-hydroxylation, chlorzoxazone 6-hydroxylation and midazolam 1'-hydroxylation. When the inhibition was greater than 20% in the assay, IC50 values were then determined. The potential in vivo bovine hepatic CYP450 inhibition by those drugs was assessed using a combination of the IC50 values and in vivo Cmax values from pharmacokinetic studies at their commercial doses and administration routes in literature. RESULTS Fifteen bovine medicines or metabolites showed in vitro inhibition on one or more bovine hepatic CYP450 metabolisms with different IC50 values. Desfuroylceftiour (active metabolite of ceftiofur), nitroxinil and flunixin have potentials to inhibit one of bovine hepatic CYP450 isoforms in vivo at their commercial doses and administration routes. The rest of the bovine medicines had low risks of in vivo bovine hepatic CYP450 inhibition. CONCLUSION This combination of in vitro assay and in vivo Cmax data provides a good approach to assess inhibition of bovine medicines on bovine hepatic CYP450.