Pharmacokinetics and CYP2D6 genotypes do not predict metoprolol adverse events or efficacy in hypertension.
OBJECTIVE
Beta-Blocker use can be associated with adverse effects that may have an impact on adherence or harm patients. The commonly prescribed beta-blocker metoprolol is metabolized by the polymorphic cytochrome P450 (CYP) 2D6 enzyme, resulting in widely variable drug exposure. We investigated whether metoprolol plasma concentrations, CYP2D6 polymorphisms, or genotype-derived phenotype was associated with adverse effects or efficacy in patients with hypertension.


METHODS
Fifty hypertensive patients received metoprolol by use of a dose-titration algorithm until target blood pressure was reached, intolerable side effects occurred, or maximal daily dose was achieved. CYP2D6 genotype was determined by methods based on polymerase chain reaction-restriction fragment length polymorphism and included 19 allelic variants. Patients were assigned to standard phenotype groups on the basis of genotype. Patients were also assigned activity scores based on functional activity of the alleles. General and dose-limiting adverse events and blood pressure responses were analyzed in relation to metoprolol steady-state pharmacokinetic profile and CYP2D6 genotype-derived phenotype.


RESULTS
Poor metabolizers had a significantly longer elimination half-life, higher S-metoprolol area under the plasma concentration-time curve (AUC), and lower oral clearance (P < or = .007 for all parameters). There was a 29.6-fold variability in AUC among extensive metabolizers, which was largely explained by CYP2D6 activity scores (P = .032 for ordered differences in AUC by activity score among extensive metabolizers). Overall general and dose-limiting adverse event rates were 46% and 14%, respectively. General adverse event rates did not differ by AUC quartile (66.7% [95% confidence interval (CI), 35.4%-88.7%] and 41.7% [95% CI, 16.5%-71.4%] in the lowest and highest quartiles, respectively; P = .09 among all quartiles). Dose-limiting adverse event rates were also not different by AUC quartile (16.7% [95% CI, 2.9%-49.1%] and 8.3% [95% CI, 0.4%-40.2%] in the lowest and highest quartiles; P = .35 among all quartiles). Furthermore, adverse event rates did not differ by activity scores or between extensive, intermediate, or poor metabolizers. Antihypertensive response rate and blood pressure changes also were not influenced by differences in plasma concentrations or CYP2D6 genotypes.


CONCLUSIONS
As expected, CYP2D6 genotype-phenotype correlates with differences in metoprolol pharmacokinetics. However, there was no association between variable pharmacokinetics or CYP2D6 genotype and beta-blocker-induced adverse effects or efficacy.
Zineh
Issam
I
Department of Pharmacy Practice, University of Florida, Gainesville, FL 32610, USA.
Beitelshees
Amber L
AL
Gaedigk
Andrea
A
Walker
Joseph R
JR
Pauly
Daniel F
DF
Eberst
Kathleen
K
Leeder
J Steven
JS
Phillips
Michael S
MS
Gelfand
Craig A
CA
Johnson
Julie A
JA
D000319:Adrenergic beta-Antagonists / Q000009:adverse effects* / Q000493:pharmacokinetics / Q000627:therapeutic use*; D000328:Adult; D000368:Aged; D019540:Area Under Curve; D001794:Blood Pressure / Q000187:drug effects / Q000235:genetics; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics*; D004305:Dose-Response Relationship, Drug; D005260:Female; D005838:Genotype; D006207:Half-Life; D006801:Humans; D006973:Hypertension / Q000188:drug therapy* / Q000235:genetics*; D008297:Male; D008790:Metoprolol / Q000009:adverse effects* / Q000493:pharmacokinetics / Q000627:therapeutic use*; D008875:Middle Aged; D010641:Phenotype; D020133:Reverse Transcriptase Polymerase Chain Reaction
D000319:Adrenergic beta-Antagonists; D019389:Cytochrome P-450 CYP2D6; D008790:Metoprolol