The influence of CYP2D6 genotype on trough plasma perhexiline and cis-OH-perhexiline concentrations following a standard loading regimen in patients with myocardial ischaemia.
OBJECTIVE
CYP2D6 protein expression is determined by the number of functional CYP2D6 alleles. It is also higher in individuals with at least one CYP2D6*2 allele. This study has investigated the effect of the number of functional CYP2D6 alleles and the influence of CYP2D6*2 alleles on plasma perhexiline concentrations in patients administered a standard loading regimen over 3 days.


METHODS
Eighteen patients with myocardial ischaemia who were not taking any drugs known to inhibit CYP2D6 metabolism in vivo commenced treatment with 200 mg of perhexiline twice per day. On the fourth day, blood was drawn for genotyping and the measurement of trough plasma concentrations of perhexiline and its major metabolite, cis-OH-perhexiline.


RESULTS
The only genotypic CYP2D6 poor metabolizer had a trough plasma perhexiline concentration of 2.70 mg l-1 and no detectable cis-OH-perhexiline. The mean+/-SD trough plasma perhexiline concentration in patients with one functional allele was significantly higher (0.63+/-0.31 mg l-1, n=8, P=0.05) than in patients with two functional alleles (0.37+/-0.17 mg l-1, n=9). Conversely, the mean metabolic ratio was significantly lower in patients with one functional allele (2.90+/-1.76, P<0.01) compared with patients with two functional alleles (6.52+/-3.26). Patients with at least one CYP2D6*2 allele had a lower plasma perhexiline concentration (0.20+/-0.09 mg l-1, n=5, P<0.001) and a higher metabolic ratio (7.86+/-2.51, P<0.01) than the non-poor metabolizer patients with no CYP2D6*2 alleles (0.62+/-0.23 mg l-1 and 3.55+/-2.54, respectively, n=12).


CONCLUSIONS
Patients with only one functional allele and not CYP2D6*2 have diminished CYP2D6 metabolic capacity for perhexiline.
Davies
Benjamin J
BJ
Department of Cardiology and Clinical Pharmacology, The Queen Elizabeth Hospital, Woodville, and Department of Clinical and Experimental Pharmacology, The University of Adelaide, South Australia.
Coller
Janet K
JK
James
Heather M
HM
Somogyi
Andrew A
AA
Horowitz
John D
JD
Sallustio
Benedetta C
BC
D000368:Aged; D000369:Aged, 80 and over; D000483:Alleles; D002317:Cardiovascular Agents / Q000097:blood* / Q000627:therapeutic use; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics*; D005787:Gene Frequency / Q000235:genetics; D005838:Genotype; D006801:Humans; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000097:blood / Q000188:drug therapy / Q000235:genetics*; D010480:Perhexiline / Q000097:blood* / Q000627:therapeutic use; D020641:Polymorphism, Single Nucleotide / Q000235:genetics
D002317:Cardiovascular Agents; D019389:Cytochrome P-450 CYP2D6; D010480:Perhexiline