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Midazolam is a phenobarbital-like cytochrome p450 inducer in rats
P A Hoen1, M K Bijsterbosch, T J van Berkel
1Leiden/Amsterdam Center for Drug Research, Division of Biopharmaceutics, Leiden, The Netherlands. p.hoen@lacdr.leidenuniv.nl
The Journal of Pharmacology and Experimental Therapeutics
|November 21, 2001
Summary
Midazolam, used to measure cytochrome P450 3A (CYP3A) levels, actually induces CYP3A1 and CYP2B expression in rats. This finding challenges its use as a reliable probe for longitudinal CYP3A studies.
Area of Science:
- Pharmacology and Toxicology
- Drug Metabolism and Pharmacokinetics
- Biochemistry
Background:
- Midazolam is primarily metabolized by cytochrome P450 3A (CYP3A) enzymes.
- Consequently, midazolam serves as a probe drug to assess CYP3A activity in vivo.
- Accurate longitudinal assessment of CYP3A expression requires the probe drug to not influence the expression of the target enzyme.
Purpose of the Study:
- To investigate whether midazolam administration affects the expression of major cytochrome P450 (CYP) isoforms in rat liver.
- To determine if midazolam's effect on CYP expression is dose-dependent and occurs in vitro.
- To evaluate the implications of these findings on the use of midazolam as a probe for CYP3A expression.
Main Methods:
- Administration of midazolam (50 mg/kg) intraperitoneally to rats for three consecutive days.
- Analysis of mRNA levels and enzyme activities of major CYP isoforms (CYP3A1, CYP3A2, CYP3A9, CYP3A18, CYP2B1/2, CYP2C6, CYP2C11, CYP2E) in rat liver.
- In vitro study using isolated rat hepatocytes treated with midazolam (100 microM) and dose-response analysis of midazolam's effect on CYP2B1/2 mRNA.
Main Results:
- Midazolam treatment significantly increased CYP3A1 mRNA levels (4-fold) and microsomal testosterone 6beta-hydroxylation activity (25%).
- A substantial induction of CYP2B1/2 mRNA (22-fold) and enzyme activity (11- to 95-fold) was observed, along with increased CYP2C6 mRNA (4-fold) and CYP2E activity (2.5-fold).
- Midazolam-induced CYP2B1/2 mRNA expression was dose-dependent, and similar induction of CYP3A1 and CYP2B was seen in isolated hepatocytes.
Conclusions:
- Midazolam acts as a phenobarbital-like inducer of multiple CYP isoforms in rats, including CYP3A1 and CYP2B.
- The induction of CYP3A1 by midazolam itself has significant implications for its use as a probe drug.
- The findings question the validity of using midazolam for longitudinal studies of CYP3A expression levels in rats.