Effects of CYP2D6 genotypes on age-related change of flecainide metabolism: involvement of CYP1A2-mediated metabolism.
OBJECTIVE
The aim of this study was to clarify the effects of CYP2D6 genotype on age-related change in flecainide metabolism in patients with supraventricular tachyarrhythmias. An in vitro study using microsomes was performed to identify other CYPs responsible for age-related change in flecainide metabolism.


METHODS
The study population comprised 111 genotyped patients: CYP2D6-homozygous extensive metabolizers (hom-EMs, n= 34), heterozygous EMs (het-EMs, n= 56), and intermediate and poor metabolizers (IMs/PMs, n= 21). Serum concentrations of flecainide and its metabolites [m-O-dealkylated flecainide (MODF) and m-O-dealkylated lactam of flecainide] were determined by use of a high-performance liquid chromatography. Metabolic ratio (MR) was expressed as serum concentrations of flecainide to its metabolites. In vitro formation of MODF was examined in human liver microsomes and cDNA-expressed CYP isoforms.


RESULTS
MR was higher in elderly patients (> or =70 years) than in middle-aged patients (<70 years). The increase of MR in elderly patients differed among CYP2D6 genotypes: 1.6-fold in het-EMs [4.3, 95% confidence interval (CI) 2.8, 5.7 vs. 2.7, 95% CI 2.3, 3.1, P < 0.05], 1.5-fold in IMs/PMs (6.0, 95% CI 4.5, 7.6 vs. 4.1, 95% CI 2.9, 5.4, P < 0.05), and no change in hom-EMs. The in vitro study using microsomes revealed that both CYP2D6 and CYP1A2 were involved in the formation of MODF. MODF formation in CYP2D6 PM microsomes increased as CYP1A2 activity increased.


CONCLUSIONS
The results suggest that patients with poor CYP2D6-mediated metabolism (het-EMs and IMs/PMs) showed age-related reduction in flecainide metabolism because metabolism was taken over by CYP1A2, whose activity decreases with age.
Doki
Kosuke
K
Department of Pharmaceutical Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Ibaraki, Japan.
Homma
Masato
M
Kuga
Keisuke
K
Aonuma
Kazutaka
K
Kohda
Yukinao
Y
D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000889:Anti-Arrhythmia Agents / Q000627:therapeutic use*; D019388:Cytochrome P-450 CYP1A2 / Q000235:genetics* / Q000378:metabolism; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics* / Q000378:metabolism; D005260:Female; D005424:Flecainide / Q000378:metabolism* / Q000627:therapeutic use; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D013617:Tachycardia, Supraventricular / Q000188:drug therapy*; D055815:Young Adult
D000889:Anti-Arrhythmia Agents; D019388:Cytochrome P-450 CYP1A2; D019389:Cytochrome P-450 CYP2D6; D005424:Flecainide