title: Evidence of CYP3A allosterism in vivo: analysis of interaction between fluconazole and midazolam.
abstract: The allosteric effect of fluconazole (effector) on the formation of 1'-hydroxymidazolam (1'-OH-MDZ) and 4-hydroxymidazolam (4-OH-MDZ) from midazolam (MDZ), a substrate of CYP3A4/5--members of the cytochrome P450 superfamily of enzymes--was examined in healthy volunteers. Following pretreatment with fluconazole, the ratio of the areas under the curve (AUCs) for 4-OH-MDZ and MDZ (AUC(4-OH)/AUC(MDZ)) increased by 35-62%, whereas the ratio AUC(1'-OH)/AUC(MDZ) decreased by 5-37%; the ratio AUC(1'-OH)/AUC(4-OH) decreased by 46-58% after fluconazole administration and had no association with the CYP3A5 genotype. The in vitro formation of 1'-OH-MDZ was more susceptible to inhibition by fluconazole than that of 4-OH-MDZ. Fluconazole decreased the intrinsic formation-clearance ratio of 1'-OH-MDZ/4-OH-MDZ to an extent that was quantitatively comparable to in vivo observations. The elimination clearance of MDZ metabolites appeared unaffected by fluconazole. This study demonstrated that fluconazole alters formation of MDZ metabolites, both in vivo and in vitro, in a manner consistent with an allosteric interaction. The 1'-OH-MDZ/4-OH-MDZ ratio may serve as a biomarker of such interactions among MDZ, CYP3A4/5, and other putative effectors.
authors: Department of Pharmaceutics, University of Washington, Seattle, Washington, USA.
authors: J
authors: J
authors: Yang
authors: W M
authors: WM
authors: Atkins
authors: N
authors: N
authors: Isoherranen
authors: M F
authors: MF
authors: Paine
authors: K E
authors: KE
authors: Thummel
mesh_terms: D000494:Allosteric Regulation; D019540:Area Under Curve; D015415:Biomarkers / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A / Q000235:genetics / Q000378:metabolism*; D004347:Drug Interactions; D015725:Fluconazole / Q000494:pharmacology*; D006801:Humans; D008874:Midazolam / Q000031:analogs & derivatives / Q000378:metabolism / Q000493:pharmacokinetics* / Q000494:pharmacology
chemical_list: D015415:Biomarkers; C042940:4-hydroxymidazolam; D015725:Fluconazole; C040081:1-hydroxymethylmidazolam; C510164:CYP3A5 protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D008874:Midazolam