Dextromethorphan and debrisoquine metabolism and polymorphism of the gene for cytochrome P450 isozyme 2D50 in thoroughbreds

Carley R. Corado, Daniel S. McKemie, Heather K Knych

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Abstract

OBJECTIVE To characterize polymorphisms of the gene for cytochrome P450 isozyme 2D50 (CYP2D50) and the disposition of 2 CYP2D50 probe drugs, dextro­methorphan and debrisoquine, in horses. ANIMALS 23 healthy horses (22 Thoroughbreds and 1 Standardbred). PROCEDURES Single-nucleotide polymorphisms (SNPs) in CYP2D50 were identified. Dis­position of dextromethorphan (2 mg/kg) and debrisoquine (0.2 mg/kg) were determined after oral (dextromethorphan) or nasogastric (debrisoquine) administration to the horses. Metabolic ratios of plasma dextromethorphan and total dextrorphan (dextrorphan plus dextrorphan-O-β-glucuronide) and 4-hydroxydebrisoquine concentrations were calculated on the basis of the area under the plasma concentration-versus-time curve extrapolated to infinity for the parent drug divided by that for the corresponding metabo­lite. Pharmacokinetic data were used to categorize horses into the pheno­typic drug-metabolism categories poor, extensive, and ultrarapid. Disposi­tion patterns were compared among categories, and relationships between SNPs and metabolism categories were explored. RESULTS Gene sequencing identified 51 SNPs, including 27 nonsynonymous SNPs. Debrisoquine was minimally detected after oral administration. Disposition of dextromethorphan varied markedly among horses. Metabolic ratios for dextromethorphan ranged from 0.03 to 0.46 (mean, 0.12). On the basis of these data, 1 horse was characterized as a poor metabolizer, 18 were char­acterized as extensive metabolizers, and 3 were characterized as ultrarapid metabolizers. CONCLUSIONS AND CLINICAL RELEVANCE Findings suggested that CYP2D50 is polymorphic and that the disposition of the probe drug varies markedly in horses. The polymorphisms may be related to rates of drug metabolism. Additional research involving more horses of various breeds is needed to fully explore the functional implica­tion of polymorphisms in CYP2D50.

Original languageEnglish (US)
Pages (from-to)1029-1035
Number of pages7
JournalAmerican Journal of Veterinary Research
Volume77
Issue number9
DOIs
StatePublished - Sep 1 2016

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ASJC Scopus subject areas

  • veterinary(all)

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