Intraindividual Blood Pressure Responses to Angiotensin‐Converting Enzyme Inhibition and Angiotensin Receptor Blockade

ACE Phenotyping as a Guide Toward Personalized Therapy With ACE Inhibitors

Background:

Angiotensin-converting enzyme (ACE) inhibitors (ACEI) are widely used in the management of cardiovascular diseases but with significant interindividual variability in the patient’s response.

Objectives:

To investigate whether interindividual variability in the response to ACE inhibitors is explained by the “ACE phenotype”—for example, variability in plasma ACE concentration, activity, and conformation and/or the degree of ACE inhibition in each individual.

Methods:

The ACE phenotype was determined in plasma of 14 patients with hypertension treated chronically for 4 weeks with 40 mg enalapril (E) or 20 mg E + 16 mg candesartan (EC) and in 20 patients with hypertension treated acutely with a single dose (20 mg) of E with or without pretreatment with hydrochlorothiazide. The ACE phenotyping included (1) plasma ACE concentration; (2) ACE activity (with 2 substrates: Hip-His-Leu and Z-Phe-His-Leu and calculation of their ratio); (3) detection of ACE inhibitors in patient’s blood (indicator of patient compliance) and the degree of ACE inhibition (ie, adherence); and (4) ACE conformation.

Results:

Enalapril reduced systolic and diastolic blood pressure in most patients; however, 20% of patients were considered nonresponders. Chronic treatment results in 40% increase in serum ACE concentrations, with the exception of 1 patient. There was a trend toward better response to ACEI among patients who had a higher plasma ACE concentration.

Conclusion:

Due to the fact that “20% of patients do not respond to ACEI by blood pressure drop,” the initial blood ACE level could not be a predictor of blood pressure reduction in an individual patient. However, ACE phenotyping provides important information about conformational and kinetic changes in ACE of individual patients, and this could be a reason for resistance to ACE inhibitors in some nonresponders.

Effectiveness, safety and cost of drug substitution in hypertension

Cost-containment measures in healthcare provision include the implementation of therapeutic and generic drug substitution strategies in patients whose condition is already well controlled with pharmacotherapy. Treatment for hypertension is frequently targeted for such measures. However, drug acquisition costs are only part of the cost-effectiveness equation, and a variety of other factors need to be taken into account when assessing the impact of switching antihypertensives. From the clinical perspective, considerations include maintenance of an appropriate medication dose during the switching process; drug equivalence in terms of clinical effectiveness; and safety issues, including the diverse adverse-event profiles of available alternative drugs, differences in the 'inactive' components of drug formulations and the quality of generic formulations. Patients' adherence to and persistence with therapy may be negatively influenced by switching, which will also impact on treatment effectiveness. From the economic perspective, the costs that are likely to be incurred by switching antihypertensives include those for additional clinic visits and laboratory tests, and for hospitalization if required to address problems arising from adverse events or poorly controlled hypertension. Indirect costs and the impact on patients' quality of life also require assessment. Substitution strategies for antihypertensives have not been tested in large outcome trials and there is little available clinical or economic evidence on which to base decisions to switch drugs. Although the cost of treatment should always be considered, careful assessment of the human and economic costs and benefits of antihypertensive drug substitution is required before this practice is recommended.

Telmisartan versus angiotension-converting enzyme inhibitors in the treatment of hypertension: a meta-analysis of randomized controlled trials

Telmisartan and angiotensin-converting enzyme inhibitors (ACEIs) are both effective and widely used antihypertensive drugs targeting renin-angiotensin-aldosterone system. The study aimed to estimate the efficacy and tolerability of telmisartan in comparison with different ACEIs as monotherapy in the treatment of hypertension. Cochrane Central Register of Controlled Trials, PubMed and Embase were searched for relevant studies. A meta-analysis of all randomized controlled trials fulfilling the predefined criteria was performed. A random-effect model was used to account for heterogeneity among trials. Twenty-eight randomized controlled trials involving 5157 patients were ultimately identified out of 721 studies. Telmisartan had a greater diastolic blood pressure (DBP) reduction than enalapril (weighted mean difference (WMD) 1.82, 95% confidence interval (CI) 0.66-2.99), ramipril (WMD 3.09, 95% CI 1.94-4.25) and perindopril (WMD 1.48, 95% CI 0.33-2.62). Telmisartan also showed a greater DBP response rate than enalapril (relative risk (RR) 1.15, 95% CI 1.05-1.26), ramipril (RR 1.34, 95% CI 1.11-1.61) and perindopril (RR 1.22, 95% CI 1.05-1.41). There was no statistical difference in DBP reduction or therapeutic response rate between telmisartan and lisinopril (WMD -0.30, 95% CI -0.65 to 0.05; RR 0.99, 95% CI 0.80-1.23, respectively). Telmisartan had fewer drug-related adverse events than enalapril (RR 0.57, 95% CI 0.44-0.74), ramipril (RR 0.44, 95% CI 0.26-0.75), lisinopril (RR 0.70, 95% CI 0.56-0.89) and perindopril (RR 0.52, 95% CI 0.28-0.98). The meta-analysis indicates that telmisartan provides a superior BP control to ACEIs (enalapril, ramipril and perindopril) and has fewer drug-related adverse events and better tolerability in hypertensive patients.

Flaws in dose-finding of antihypertensive drugs

The random variation of BP and the intraindividual variation in the BP response to treatment cause considerable difficulties in the evaluation of the dose-response relationship of antihypertensive drugs. Thus, failures in finding the optimal dose of antihypertensive drugs have not been uncommon. The notion that angiotensin receptor antagonists (angiotensin receptor blockers) have a relatively flat dose-response relationship also appears to be due to limitations of dose-finding studies. The conventional method of office BP measurement that is typically used in dose-finding studies is poorly reproducible and is subject to the white coat effect, placebo effect, and observer bias. These problems can be overcome by using ambulatory or home BP monitoring, which are known to improve the accuracy of studies aiming to detect BP changes. A crossover design study allows all participants to receive all treatments (doses) and paired comparisons are performed. Thus, this design significantly enhances the power to detect differences between doses, compared with the typical parallel-group dose-finding study. A separate analysis of the dose-response relationship exclusively in subjects with a good BP response to the drug (responders) can provide clear insight about the drug effect when it actually works. These measures improve the accuracy of drug trials investigating the dose-response relationship and might prevent misleading information at an early stage of clinical development.

Combination pharmacotherapy in hypertension

Combination pharmacotherapy with two or more drugs is required in order to reach the currently recommended blood pressure goals in the majority of hypertensive patients, particularly those with a goal of <130/80 mm Hg. Further to the potentiation of the antihypertensive effects, benefits of combination therapy include the potential of fewer adverse affects and of improvement of patients' compliance. Current guidelines recommend that combination pharmacotherapy might also be considered as initial treatment in patients with significant elevation of blood pressure and evidence of complications. Several effective and well-tolerated antihypertensive drug classes available today offer multiple options for combination therapy. The choice of antihypertensive agents should be made on the basis of current recommendations regarding first line drugs and compelling indications. Specific drug combinations might have additional beneficial or detrimental long-term metabolic effects, beyond their effects on blood pressure. However, more outcome data comparing antihypertensive drug combinations are required. The implementation of an intensive up-titration treatment strategy, together with a systematic use of full doses of multiple drug combinations, is expected to achieve optimal blood pressure control in the vast majority of hypertensive patients.