Beneficial effects of betaxolol, a selective antagonist of beta-1 adrenoceptors, on exercise-induced myocardial ischemia in patients with coronary vasospasm

Association of CYP2D6 and ADRB1 genes with hypotensive and antichronotropic action of betaxolol in patients with arterial hypertension

Betaxolol is a selective antagonist of beta(1)-adrenergic receptors. Personal response to the drug widely varies and depends on its properties and individual features including innate characteristics. Our aim was to study the association between the clinical response to betaxolol in patients with essential hypertension (EH) and polymorphous markers of two genes: beta(1) adrenergic receptor gene (ADRB1) and cytochrome P450 2D6 gene (CYP2D6). Eighty-one patients with EH were selected. Mean age was 52.2 +/- 1.22 years. Betaxolol monotherapy provided effective blood pressure control (BP < 140/90 mmHg) in 68 patients, 56 of them continued treatment with initial dose. The systolic (SBP) and diastolic (DBP) blood pressure declined significantly at the end of the study. We have not found any significant association of rest and exercise BP and heart rate (HR) with polymorphous marker Arg389Gly of ADRB1 gene except the nighttime variability of DBP. But in case of the polymorphous marker Pro34Ser of CYP2D6 gene we have found significant association with response to betaxolol therapy. The rest HR declined more significantly in Ser/Pro genotype carriers (-32.6 +/- 4.77 beats/min and -18.4 +/- 2.01 beats/min, P = 0.023). These patients demonstrated more significant increase of exercise time (4.58 +/- 0.90 and 0.59 +/- 0.58 min, P = 0.045). Maximal exercise HR and DBP were also significantly lower in Ser/Pro genotype carriers in comparison with Ser/Ser genotype carriers. Decline of mean daytime SBP in 24-h ambulatory blood pressure monitoring was more significant in Pro allele carriers (-21.0 +/- 2.55 mmHg vs. -5.2 +/- 2.27 mmHg in patients with Ser/Ser genotype, P = 0.001). Betaxolol effect on HR and BP significantly depends on variability of the gene determining the drug metabolism. The carriers of Pro34 allele of CYP2D6 gene (8.6%) are more sensitive to betaxolol therapy. Because of the relatively small group sizes our data should be considered as preliminary ones. The increase of our groups and the replication in other studies will permit to estimate the contribution of genetic factors to betaxolol effect on HR and BP.

Effect of betaxolol hydrochloride on heart rate variability indices during exercise stress testing in patients with hypertension

Betaxolol hydrochloride is a beta1-selective antagonist that produces vasodilation in patients with hypertension and ischemic heart disease. The goal of the present study was to characterize the effect of betaxolol on heart rate variability indices (HRV), a well-established prognostic marker. Symptom limited-treadmill exercise testing was performed in 17 hypertensive patients (60.9 +/- 14.8 years-old) before and immediately a 3 weeks course of betaxolol hydrochloride (5 mg daily). Frequency domain HRV (high frequency spectra, HF; 0.15-0.40 Hz: low frequency spectra, LF; 0.04-0.15 Hz) was measured during exercise treadmill testing using MemCalc software. Betaxolol hydrochloride significantly decreased the maximal systolic blood pressure and heart rate (184 +/- 29 vs. 156 +/- 26 mmHg, P < 0.01; 132 +/- 21 vs. 113 +/- 15 bpm, P < 0.01) and significantly increased HF and LF during exercise treadmill testing (HF, 32 +/- 36 vs. 56 +/- 55 men/Hz, P < 0.01; LF, 64 +/- 58 vs. 95 +/- 86 men/Hz, P < 0.01). Thus, treatment with betaxolol hydrochloride resulted in a decrease in blood pressure during exercise treadmill testing and in an increase in HRV. This suggests that this agent could have beneficial effects on long-term prognosis in patients with hypertension.