A Nanogram Dose of the CYP3A Probe Substrate Midazolam to Evaluate Drug Interactions

Abstract

The objective of the study was to establish an in vivo method for assessing cytochrome P450 3A (CYP3A) activity using therapeutically inert nanogram doses of midazolam. We administered four escalating single doses of oral midazolam (0.0001-3 mg) to 12 healthy participants, stratified according to CYP3A5 carrier status, to assess pharmacokinetics linearity. We then evaluated the interactions with the CYP3A inhibitor ketoconazole (400 mg q.d.) after nanogram and regular doses of midazolam. Area under the plasma concentration-time curve (AUC) and peak plasma concentration (C(max)) were linear over the entire range of doses. Ketoconazole reduced midazolam oral clearance by 92.8%. AUC and C(max) increased by 1,540 and 363%, respectively. CYP3A5 carrier status had no influence on midazolam oral clearance or its inhibition by ketoconazole. This is the first study showing that midazolam pharmacokinetics is linear in a 30,000-fold concentration range, and therefore that nano- and microgram doses of midazolam can reliably predict the pharmacokinetics of midazolam in therapeutic doses and can be used to assess CYP3A activity even in the presence of strong CYP3A inhibitors.

Midazolam microdose to determine systemic and pre‐systemic metabolic CYP3A activity in humans

“…While our earlier study already suggested that absorption was linear in the range between 100 ng and 3 mg direct intra-individual comparison with intravenous pharmacokinetics has now confirmed this earlier finding [11].…”

“…Therefore, and in accordance with our earlier findings [11], we anticipated linearity of the pharmacokinetics intravenous doses, and dose-normalized values for Cmax and AUC indeed well compared with the data of the former study. The same was true for clearances, half-lives and volumes of distribution.…”

“…We have previously shown that oral doses of midazolam exhibit linear pharmacokinetics over a 30 000-fold range and that oral microdoses can successfully predict drug interactions with strong inhibitors of CYP3A in healthy volunteers [11] and patients with haematological diseases [12]. Microdosing refers to the concept of administering 1% of a pharmacologically active dose of a substance or 100 μg, whatever is less, to study a substance's property.…”

In vitro ketamine CYP3A‐mediated metabolism study using mammalian liver S9 fractions, cDNA expressed enzymes and liquid chromatography tandem mass spectrometry

“…In vitro metabolism studies revealed that the principal hepatic metabolite of ketamine was norketamine and the formation was principally catalyzed by CYP3A [Mössner et al 2011;Kwan and Thormann, 2011]. Hence, midazolam is a wellcharacterized CYP3A substrate used for in vitro and in vivo metabolism studies [Halama et al, 2013;Mooiman et al, 2013]. One objective was to verify if midazolam could affect ketamine metabolism in rat, dog and human S9 liver fractions.…”

“…Midazolam is the preferred phenotyping CYP3A4 probe substrate used for in vitro and in vivo studies [Halama et al, 2013;Mooiman et al, 2013]. Co-administration of ketamine and midazolam to animals or humans could lead to competitive inhibition of CYP3A and result in an increase of systemic concentrations.…”