European Journal of Cardiovascular Medicine

Hypertension is a leading modifiable risk factor for cardiovascular morbidity and mortality worldwide and a major driver of stroke, coronary disease and renal failure [1,2]. Despite multiple effective drug classes, inter-individual variability in blood-pressure (BP) response to antihypertensive agents remains large, contributing to suboptimal control in many patients [1]. Genetic variation is one important contributor to this variability, and pharmacogenomic approaches are increasingly investigated as a way to individualize antihypertensive therapy [1].

The cytochrome P450 3A (CYP3A) subfamily — notably CYP3A4 and CYP3A5 — plays a central role in the hepatic metabolism of many calcium-channel blockers including amlodipine [3,4]. The CYP3A5 *6986A>G (rs776746, *3) allele results in aberrant splicing and minimal or absent CYP3A5 expression, whereas carriers of the *1 allele typically express functional enzyme; allele frequencies vary markedly between ethnic groups [3]. Pharmacokinetic studies in healthy volunteers have demonstrated that CYP3A5 genotype influences amlodipine disposition: carriers of functional CYP3A5 alleles show differences in clearance and exposure compared with *3/*3 homozygotes, providing a plausible mechanistic basis for genotype-dependent pharmacodynamic effects [4].

Clinical investigations of CYP3A5 and related CYP3A polymorphisms in relation to amlodipine efficacy have produced inconsistent results across populations. Some cohort studies and a review concluded that CYP3A5 and CYP3A4 variants can alter antihypertensive response, but effects differ by ethnic group and clinical setting [2,4,5]. For example, analysis from a high-risk African-American cohort did not find a clear association between CYP3A5 A6986G and BP response, whereas studies in Chinese patients — including those after renal transplantation — reported stronger associations between CYP3A5*3 (and linked CYP3A4 alleles) and amlodipine efficacy [5,6]. These discordant findings highlight the need for population-specific data and for studies that combine genotype, standardized dosing and prospective BP assessment.

Given the mechanistic plausibility and variable clinical evidence, this study was designed to evaluate the impact of CYP3A5 genetic polymorphism on BP response to amlodipine in a prospectively followed cohort. Clarifying genotype–phenotype relationships in our population may inform whether pharmacogenetic testing could meaningfully guide calcium-channel blocker therapy.

Study Design and Setting: A prospective, observational study was conducted at a tertiary care teaching hospital in India. All participants provided written informed consent before enrolment.

Study Population: Adult patients aged between 30 and 65 years who were newly diagnosed with essential hypertension (systolic blood pressure ≥140 mmHg and/or diastolic blood pressure ≥90 mmHg on two separate occasions, as per the Joint National Committee 8 criteria [7]) were included. Patients with secondary hypertension, renal impairment, hepatic dysfunction, pregnancy, or those receiving any other antihypertensive medication were excluded.

Sample Size: A total of 120 patients were enrolled for the study, calculated using the formula for comparison of means with an expected effect size of 0.5, power of 80%, and significance level of 0.05. This sample size was deemed adequate to detect clinically relevant differences in antihypertensive response among different genetic variants.

Drug Intervention: All eligible participants were initiated on amlodipine (5 mg once daily) as monotherapy for a minimum duration of 8 weeks. Dosage adjustments were allowed up to 10 mg daily, based on clinical response and tolerability, in accordance with standard treatment guidelines.

Assessment of Drug Response: Blood pressure measurements were obtained in the sitting position using a calibrated sphygmomanometer. Three readings were taken at 5-minute intervals, and the average was recorded. Response to therapy was defined as a reduction in systolic blood pressure by ≥10 mmHg or diastolic blood pressure by ≥5 mmHg after 8 weeks of therapy.

Genetic Analysis: 5 ml of peripheral venous blood were collected in EDTA tubes from each participant before starting the treatment. Genomic DNA was extracted using a standard phenol-chloroform method. Polymerase Chain Reaction (PCR) followed by Restriction Fragment Length Polymorphism (RFLP) analysis was used to detect polymorphisms in the CYP3A5 (6986A>G) gene, which is known to influence calcium channel blocker metabolism. Genotypes were categorized as expressors (CYP3A51/*1 or *1/3) and non-expressors (CYP3A53/3) based on allele distribution.

Data Collection and Analysis: Baseline demographic, anthropometric, and clinical parameters were recorded using a structured proforma. Blood pressure readings before and after treatment were compared within and between genotype groups. Data were analyzed using SPSS version 25.0 (IBM Corp., USA). Continuous variables were expressed as mean ± standard deviation (SD) and compared using Student’s t-test or ANOVA, while categorical variables were analyzed using the Chi-square test. A p-value <0.05 was considered statistically significant.

A total of 120 patients newly diagnosed with essential hypertension were included in the study. Among them, 66 (55%) were males and 54 (45%) were females, with a mean age of 52.4 ± 8.6 years. The mean body mass index (BMI) of the participants was 26.7 ± 3.5 kg/m². No statistically significant differences were observed in baseline demographic or clinical variables between the CYP3A5 expressor and non-expressor groups (Table 1).

Table 1: Demographic and Baseline Characteristics of Study Participants (n = 120)

Genotyping analysis of the CYP3A5 (6986A>G) polymorphism revealed that 14 patients (11.7%) carried the *1/*1 genotype, 34 (28.3%) were heterozygous *1/*3, and 72 (60.0%) possessed the *3/*3 genotype (Table 2). Overall, 48 participants (40%) were categorized as expressors (either *1/*1 or *1/*3), while 72 (60%) were non-expressors (*3/*3). The genotype frequencies were consistent with Hardy–Weinberg equilibrium.

Table 2: Distribution of Genotypes of CYP3A5 (6986A>G) Polymorphism

Following eight weeks of treatment with amlodipine, a significant reduction in both systolic and diastolic blood pressures was observed across all participants. The mean decrease in systolic blood pressure was 17.2 ± 6.3 mmHg among expressors, compared with 13.9 ± 6.8 mmHg among non-expressors (p = 0.02). Similarly, diastolic blood pressure reduction was greater in expressors (13.2 ± 4.5 mmHg) than in non-expressors (10.8 ± 4.9 mmHg, p = 0.01). Post-treatment systolic and diastolic blood pressures were significantly lower in the expressor group compared to the non-expressor group (Table 3).

Table 3: Change in Blood Pressure after 8 Weeks of Amlodipine Therapy

When treatment response was defined as a reduction of ≥10 mmHg in systolic or ≥5 mmHg in diastolic blood pressure, 85 patients (70.8%) were categorized as responders. The proportion of responders was significantly higher in the expressor group (81.3%) compared with non-expressors (63.9%) (p = 0.04) (Table 4).

Table 4: Distribution of Responders and Non-Responders by Genotype

Amlodipine was generally well tolerated. The most frequently reported adverse effects were pedal edema (10.0%) and headache (6.7%). The overall incidence of adverse effects was slightly higher among non-expressors (23.6%) than expressors (18.7%), although the difference was not statistically significant (p = 0.52) (Table 5). None of the patients discontinued treatment due to adverse effects.

Table 5: Adverse Effects Observed During the Study

In this prospective cohort, carriers of functional CYP3A5 alleles (*1/*1 or *1/3) experienced significantly greater reductions in both systolic and diastolic blood pressure after eight weeks of amlodipine compared with *3/*3 non-expressors. These findings are consistent with the mechanistic expectation that CYP3A5 expression alters amlodipine disposition and thereby modulates pharmacodynamic effect. Pharmacokinetic investigations have shown that CYP3A5 genotype affects clearance and systemic exposure of CYP3A substrates, providing a biologic rationale for the phenotype observed here [8].

Several clinical studies have reported associations between CYP3A5 (and linked CYP3A4) variants and differential responses or adverse effects to dihydropyridine calcium-channel blockers. In cohorts of East Asian patients, polymorphisms in CYP3A5 have been linked both to efficacy and to amlodipine-related peripheral edema, supporting the possibility of clinically meaningful genotype–drug interactions in some populations. [9,10] A number of smaller prospective studies and single-center reports also documented genotype-dependent differences in blood-pressure lowering with amlodipine, particularly when dosing and outcome assessment were standardized [11,12].

Conversely, other investigations have failed to find consistent associations, and the literature remains heterogeneous. Several candidate-gene studies reported no significant impact of CYP3A53 (or of CYP3A41G) on amlodipine plasma concentration or BP response in their samples, highlighting interstudy variability that may reflect differences in ethnicity, sample size, study design, co-medications, and phenotype definitions [5,13]. Large population analyses and recent comprehensive reviews emphasize that while pharmacogenomic markers show promise, results vary across ethnic groups and are not yet uniformly predictive for routine clinical use [14,15].

Our findings therefore add to evidence that CYP3A5 genotype can influence amlodipine response in certain populations. The stronger response seen in expressors in our cohort may reflect increased local or systemic drug activation/clearance dynamics that translate into larger net hemodynamic effects; alternatively, genotype may be in linkage disequilibrium with other functional variants that affect drug targets or downstream pathways [8,10]. The observed similarity in adverse-event rates between genotype groups in this study suggests that efficacy differences were not accompanied by a proportional increase in common dose-related adverse effects, although our study was not powered to detect small differences in safety outcomes.

Limitations of the present study should be acknowledged. First, the single-gene candidate approach does not capture the polygenic and non-genetic determinants of antihypertensive response — such as variants in drug-transporters, receptor genes, comorbidities, dietary sodium, and drug–drug interactions — which may attenuate or amplify genotype effects [14]. Second, the relatively modest sample size and single-center design limit generalizability; population allele frequencies and gene-environment interactions differ by ancestry and geographic region, which likely contributes to the inconsistent results reported across studies. [5,11] Third, follow-up was limited to eight weeks and a single drug (amlodipine); longer observation and assessment of dose-response relationships would provide additional clinical context. Finally, while PCR–RFLP (or mass-array) genotyping reliably identifies common alleles, rare or structural variants not assayed here could affect phenotype.

CYP3A5 genetic polymorphism significantly affects the antihypertensive response to amlodipine. Patients with the expressor genotype (*1/*1 or *1/3) showed greater blood pressure reduction than non-expressors (*3/3). These findings highlight the potential role of pharmacogenetic testing in individualizing antihypertensive therapy for better clinical outcomes.

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