The CYP2C9 genotype predicts the blood pressure response to irbesartan: results from the Swedish Irbesartan Left Ventricular Hypertrophy Investigation vs Atenolol (SILVHIA) trial

BACKGROUND The cytochrome P450 CYP2C9 enzyme (CYP2C9) metabolizes many clinically important drugs, for example, phenytoin, warfarin and the angiotensin II type 1 (AT1) receptor antagonists, losartan and irbesartan. Single nucleotide polymorphisms in the CYP2C9 gene result in the expression of three important variants, CYP2C9*1 (wild-type), CYP2C9*2 and CYP2C9*3, the last two exhibiting reduced catalytic activity compared with the wild-type. The CYP2C9 genotype is known to determine sensitivity to and dose requirements for both warfarin and phenytoin, and also the rate of metabolism of losartan. However, its influence on clinical response to treatment with the AT1 receptor antagonist, irbesartan, has not been investigated. OBJECTIVE To determine whether the CYP2C9 genotype influences the blood pressure-decreasing response to antihypertensive treatment with irbesartan. DESIGN AND METHODS One hundred and two patients with essential hypertension and left ventricular hypertrophy were allocated randomly to groups to receive double-blind treatment with either irbesartan (n = 49) or the β1-adrenergic receptor blocker, atenolol (n = 53). Blood pressure was measured before and after 12 weeks of treatment. CYP2C9 genotyping was performed using solid-phase minisequencing. RESULTS The diastolic blood pressure (DBP) response differed in relation to the CYP2C9 genotype in patients given irbesartanthe reduction in patients with genotype CYP2C9*1/ CYP2C9*1 (n = 33) was 7.5% and that with CYP2C9*1/ CYP2C9*2 (n = 12) was 14.4% (P = 0.036). A similar trend was seen for systolic blood pressure. In contrast, no relation was seen between the CYP2C9 genotype and blood pressure response to atenolol, a drug not metabolized via CYP2C9. CONCLUSIONS The CYP2C9 genotype seems to predict the DBP response to irbesartan, but not to atenolol, in patients with essential hypertension.