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AIMS: Terodiline has concentration dependent QT prolonging effects and thus the potential for cardiotoxicity. Pharmacogenetic variation in terodiline metabolism could be responsible for cardiotoxicity. We sought to determine whether CYP2D6 (debrisoquine hydroxylase) or CYP2C19 (S-mephenytoin hydroxylase) status is a risk factor for terodiline cardiotoxicity. METHODS: Using the UK Yellow Card scheme to identify patients, blood samples were obtained from eight patients who survived ventricular tachycardia or torsades de pointes suspected to be due to terodiline, for determination of CYP2D6 and CYP2C19 genotypes. Genotype prevalence was compared with that in published general population groups. RESULTS: One patient was a CYP2D6 poor metaboliser (CYP2D6*4 homozygous) and a second was heterozygous for CYP2D6*4, a slightly lower frequency for these genotypes compared with the general population (P = 0.31). In the case of CYP2C19, one patient was a poor metaboliser and four were heterozygous for the variant CYP2C19*2 allele, compared with general population frequencies of 2% and 23%, respectively (P = 0.035). CONCLUSIONS: These findings suggest that debrisoquine poor metaboliser status is not primarily responsible for terodiline cardiotoxicity. However, possession of the CYP2C19*2 allele appears to contribute to adverse cardiac reactions to terodiline. The present study demonstrates the feasibility of using spontaneous adverse drug reaction reporting schemes to determine the contribution of genotype for metabolizing enzymes to uncommon adverse drug reactions.

Original publication

DOI

10.1046/j.1365-2125.2000.00230.x

Type

Journal article

Journal

Br J Clin Pharmacol

Publication Date

07/2000

Volume

50

Pages

77 - 80

Keywords

Aged, Aged, 80 and over, Alleles, Aryl Hydrocarbon Hydroxylases, Butylamines, Cytochrome P-450 CYP2C19, Cytochrome P-450 CYP2D6, Cytochrome P-450 Enzyme System, DNA, Debrisoquin, Female, Follow-Up Studies, Gene Frequency, Genotype, Heart, Humans, Male, Mixed Function Oxygenases, Parasympatholytics, Polymerase Chain Reaction, Polymorphism, Genetic, Tachycardia, Ventricular, Torsades de Pointes