Inhibitory effects of trospium chloride on cytochrome P450 enzymes in human liver microsomes.

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Beckmann-Knopp S, Rietbrock S, Weyhenmeyer R, Bocker RH, Beckurts KT, Lang W, Fuhr U

Inhibitory effects of trospium chloride on cytochrome P450 enzymes in human liver microsomes.

Pharmacol Toxicol. 1999 Dec;85(6):299-304.

PubMed ID

10628907 [ View in PubMed

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Abstract

Trospium chloride, an atropine derivative used for the treatment of urge incontinence, was tested for inhibitory effects on human cytochrome P450 enzymes. Metabolic activities were determined in liver microsomes from two donors using the following selective substrates: dextromethorphan (CYP2D6), denitronifedipine (CYP3A4), caffeine (CYP1A2), chlorzoxazone (CYP2E1), S-(+)-mephenytoin (CYP2C19), S-(-)-warfarin (CYP2C9) and coumarin (CYP2A6). Incubations with each substrate were carried out without a possible inhibitor and in the presence of trospium chloride at varying concentrations (37-3000 microM) at 37 degrees in 0.1 M KH2PO4 buffer containing up to 3% DMSO. Metabolite concentrations were determined by high-performance liquid chromatography (HPLC) in all cases except CYP2A6 where direct fluorescence spectroscopy was used. First, trospium chloride IC50 values were determined for each substrate at respective K(M) concentrations. Trospium chloride did not show relevant inhibitory effects on the metabolism of most substrates (IC50 values considerably higher than 1 mM). The only clear inhibition was seen for the CYP2D6-dependent high-affinity O-demethylation of dextromethorphan, where IC50 values of 27 microM and 44 microM were observed. Therefore, additional dextromethorphan concentrations (0.4-2000 microM) were tested. Trospium chloride was a competitive inhibitor of the reaction with Ki values of 20 and 51 microM, respectively. Thus, trospium chloride has negligible inhibitory effects on CYP3A4, CYP1A2, CYP2E1, CYP2C19, CYP2C9 and CYP2A6 activity but is a reasonably potent inhibitor of CYP2D6 in vitro. Compared to therapeutic trospium chloride peak plasma concentrations below 50 nM, the 1000-times higher competitive inhibition constant Ki however suggests that inhibition of CYP2D6 by trospium chloride is without any clinical relevance.

DrugBank Data that Cites this Article

Drug Enzymes

Drug	Enzyme	Kind	Organism	Pharmacological Action	Actions
Trospium	Cytochrome P450 2D6	Protein	Humans	Unknown	Inhibitor	Details