An interaction between the cytochrome P450 probe substrates chlorzoxazone (CYP2E1) and midazolam (CYP3A)

Abstract

Aims The use of multiple probe substrates to evaluate the activity of drug metabolizing enzymes requires that there are no inter±substrate interactions. As part of a series of studies to develop a clinically useful collection of probe substrates that could be given alone or in any combination, we observed an interaction between midazolam (MDZ) and another component of the six-drug cocktail. Published data indicated that the interacting component was likely to be chlorzoxazone. This was investigated as part of a second study. The data relating to the interaction from both studies are reported here. Methods Both studies were performed in 16 healthy subjects. All treatments were given orally after an overnight fast. In study 1, which was performed to a four-period, open, crossover design, subjects received on separate occasions MDZ 5 mg, diclofenac 25 mg, a four drug cocktail (caffeine 100 mg, mephenytoin 100 mg, debrisoquine 10 mg and chlorzoxazone 250 mg) and a six drug cocktail (caffeine 100 mg, mephenytoin 100 mg, debrisoquine 10 mg, chlorzoxazone 250 mg, diclofenac 25 mg and MDZ 5 mg). In study 2, which was performed to a two-period, open, crossover design, subjects received a ®ve drug cocktail (as the six drug cocktail in the ®rst study, but without chlorzoxazone and with diclofenac dose increased to 50 mg) and a six drug cocktail (as ®ve drug cocktail, with chlorzoxazone 250 mg). In both studies, blood samples were taken for measurement of plasma MDZ and 1-hydroxy MDZ (1-OH MDZ) concentrations. In study 1, blood samples were taken up to 12 h post-dose while in study 2 a single sample was taken 2 h after dosing. In study 1, the potential interaction between MDZ and the other components of the six drug cocktail was assessed by comparing AUC last ratios (1-OH MDZ/MDZ) between the two treatments. Additionally, a single sampling timepoint of 2 h post-dose for determination of concentration, rather than AUC, ratios was established. The 2 h plasma concentration ratios from studies 1 and 2 were combined and a pooled analysis performed to compare ratios within each study (to determine the change in ratio when MDZ was dosed with and without chlorzoxazone) and between studies (to determine the consistency of the ratios when MDZ was given either as part of the two six drug cocktails or when given alone and as part of the ®ve drug cocktail). Results In study 1, both the AUC last ratio and the 2 h post-dose plasma concentration ratio were reduced when MDZ was given as part of the six drug cocktail in comparison with those for MDZ alone. This was the result of an increase in MDZ, rather than decrease in 1-OH MDZ, concentrations and was considered to result from a reduction in ®rst pass metabolism of MDZ. The geometric mean AUC last values (with 95% CI) for MDZ were 95.6 (79.0, 115.7) and 160.4 (133.6, 192.6) mg l x1 h when given alone and as part of the six drug cocktail, respectively. The corresponding values for 1-OH MDZ were 789.6 (697.6, 893.6) and 791.4 (701.7, 892.6) mg l x1 h. The ratio of adjusted geometric mean ...

THE CONDUCT OF IN VITRO AND IN VIVO DRUG-DRUG INTERACTION STUDIES: A PHARMACEUTICAL RESEARCH AND MANUFACTURERS OF AMERICA (PhRMA) PERSPECTIVE

“…Using a combination of quinidine and rifampin with the five P450 probe substrate mixture, selective enzyme inhibition and induction of multiple enzymes were demonstrated (Branch et al, 2000). Despite these initial promising results, subsequent studies identified an interaction between chlorzoxazone (CYP2E1) and midazolam (CYP3A) (Palmer et al, 2001).…”

Effect of propiverine on cytochrome P450 enzymes: a cocktail interaction study in healthy volunteers

“…In contrast to other existing cocktails (e.g., Frye et al, 1997;Palmer et al, 2001;Blakey et al, 2004), the cocktail used here has several useful peculiarities, including semisequential midazolam administration, allowing the assessment of hepatic and intestinal CYP3A4 activity within 1 day; low doses for all substances, minimizing the risk for adverse reactions; the inclusion of optional cocktail components; and the use of fully validated metrics for all P450s included.…”

“…Here, the low-dose cocktail strategy could be shown to be an effective tool to assess the drug-drug interactions profile of propiverine in vivo. All probe substrates used in this cocktail approach have been previously shown to be enzyme-selective substrates without relevant mutual interaction in vivo (Endres et al, 1996;Frye et al, 1997;Streetman et al, 2000b;Bruce et al, 2001;Palmer et al, 2001;Wang et al, 2001;Zhu et al, 2001;Blakey et al, 2004). The composition of the cocktail used here was tailored primarily with respect to the previous information obtained in in vitro studies, suggesting that any clinically relevant interaction of propiverine with cytochrome P450 enzymes as a substrate, inhibitor, and/or inducer would mainly concern CYP3A4 and possibly also CYP2C9 and/or CYP2C19.…”

Interactions of Herbs with Cytochrome P450

“…However, the value of the cocktail approach may be limited due to marked intrasubject variability and the possibility of interaction between the coadministered probes. Palmer et al (2001) reported that chlorzoxazone significantly altered the pharmacokinetics of oral midazolam, perhaps through inhibition of first-pass metabolism by CYP3A in the intestine.…”