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Thursday, March 26, 2009

Blood pressure lowering efficacy of angiotensin converting enzyme (ACE) inhibitors for primary hypertension

With the popularity of ACE inhibitors in mind, investigators conducted a systematic review of published studies to determine how effective the drugs actually are in reducing blood pressure. They also examined dose effectiveness, adverse effects, and the role of co-occurring conditions.

The Study Findings

Researchers looked for double-blind studies comparing ACE inhibitors and placebo. All included studies were at least 3 weeks in duration and measured blood pressure as an endpoint at 3-12 weeks. Studies that featured a response-dependent titration of medications were included in the review. Only research that focused on patients with a blood pressure above 140/90 mm Hg was reviewed.

The review included 92 trials with a total of 12,954 participants (mean age, 54 years). Mean baseline blood pressure was 157/101 mm Hg and mean pulse pressure was 56 mm Hg. The majority (75%) of included studies was industry-sponsored, and 82% of the trials examined fixed-dose ACE inhibitors. The duration of trials was generally short, which limited data with regard to adverse events and study withdrawals.

The main potential source of bias in the research was a lack of information with regard to how the studies were blinded. In addition, the reviewers suggested that the researchers could have preferentially selected patients more likely to respond to ACE inhibitors. This selection bias could make ACE inhibitors appear more effective than they truly are.

The studies covered 14 ACE inhibitors. The degree of homogeneity with regard to their efficacy in reducing blood pressure was remarkable. No one medication appeared superior to others.

Overall, ACE inhibitors had a modest collective effect in reducing blood pressure. The mean reduction in systolic blood pressure ranged between 6 mm Hg and 9 mm Hg, and the mean reduction in diastolic blood pressure was 4-5 mm Hg. Less data were available with regard to the blood pressure effects of ACE inhibitors at 1-12 hours after dosing, but the average decrease in blood pressure with ACE inhibitors around their peak concentration was greater than their average efficacy (11.4/6.4 mm Hg).

Dose Effectiveness

The study provided some important information about the relationship between the dose of ACE inhibitors and their effect on blood pressure. Doses lower than the manufacturers' maximum recommended dosage had the same blood pressure-lowering effect as the maximum dose. For example, doses of one eighth to one quarter of the maximum achieved the blood pressure-lowering effect of the maximum dose in 60% to 70% of cases. Half of the maximum dose achieved it 90% of the time. There was no blood pressure-lowering effect at or below one sixteenth of the maximum suggested dose. These data suggest that use of the maximum dosage of ACE inhibitors to achieve greater blood pressure control is usually unnecessary.

The research also identified dosing information for individual ACE inhibitors and suggested that the manufacturers' recommended starting doses of benazepril, moexipril, and ramipril are higher than the minimum dose needed to reduce blood pressure. Conversely, captopril did not appear effective in reducing blood pressure at the manufacturers' recommended starting dose. Most of the maximum blood pressure-lowering effect of lisinopril was achieved at only one eighth of the recommended maximum dose.

ACE inhibitor dosing was also one of the biggest deficits in the current review. It was clear to the review authors that not all data in regard to the efficacy of different doses of ACE inhibitors were published. Instead, the data were supplied to regulators privately to determine the appropriate dosing range of ACE inhibitors.

Only half of trials provided data in regard to the rate of withdrawal due to adverse events. Collectively, there was no difference between ACE inhibitors and placebo in this critical outcome. ACE inhibitors did not significantly affect patients' heart rate.

Addressing Other Health Issues

Physicians might choose ACE inhibitors to treat hypertension for other possible health benefits associated with these medications, especially the potential to prevent type 2 diabetes. ACE inhibitors can have a positive effect on glucose metabolism through multiple mechanisms, and previous research suggested that they could prevent incident diabetes compared with other antihypertensive medications. Specifically, the Captopril Prevention Project demonstrated a 14% relative reduction in this outcome among participants receiving captopril vs a diuretic or beta-blocker. This benefit, associated with captopril, was evident regardless of the baseline risk for diabetes, although the incidence of diabetes was not a primary outcome of the study.

The Diabetes Reduction Assessment with Ramipril and Rosiglitazone Medication (DREAM) trial directly examined the effect of ramipril vs placebo on the incidence of diabetes. This study examined patients with impaired fasting glucose levels or reduced insulin sensitivity but no history of cardiovascular disease. After a median of 3 years of treatment, ramipril was not associated with a significantly lower incidence of diabetes compared with placebo. Median fasting plasma glucose levels were also similar at the end of the trial. However, ramipril was associated with a higher rate of return to normoglycemia.

Physicians might also consider using ACE inhibitors for hypertension in order to prevent incident heart failure. However, although ACE inhibitors are associated with numerous positive outcomes, including reduced mortality, among patients with known heart failure, little evidence exists that they provide special protection against new heart failure. In a study of quinapril and placebo initiated shortly after myocardial infarction, there was no difference between treatment groups in a composite outcome of cardiovascular death and significant cardiovascular events. Specifically, no difference was found in the risk for heart failure among those patients at high cardiovascular risk. Similarly, in the Antihypertensive and Lipid-Lowering Treatment to Prevent Hearth Attack Trial (ALLHAT), the incidence of heart failure was similar among patients receiving lisinopril and chlorthalidone.

Commentary

Although ACE inhibitors may not provide special protection against diabetes or heart failure among patients with hypertension, physicians should still consider these medications when managing hypertension. In fact, the nature of hypertension management dictates that they have to because most patients require more than 1 medication initially. In a recent study of men receiving care at a Veteran Affairs hospital, 60.4% of subjects with hypertension and significant cardiovascular risk were receiving multiple antihypertensive medications. Nevertheless, only 28% of these same patients had reached their goal blood pressure levels, indicating that they needed titration of their medications, if not the addition of other antihypertensive drugs.

Authors' conclusions

There are no clinically meaningful BP lowering differences between different ACE inhibitors. The BP lowering effect of ACE inhibitors is modest; the magnitude of trough BP lowering at one-half the manufacturers' maximum recommended dose and above is -8/-5 mm Hg. Furthermore, 60 to 70% of this trough BP lowering effect occurs with recommended starting doses. The review did not provide a good estimate of the incidence of harms associated with ACE inhibitors because of the short duration of the trials and the lack of reporting of adverse effects in many of the trials.

Clinical Pearls

  • In the current review, ACE inhibitors were associated with an average reduction in systolic blood pressure between 6 mm Hg and 9 mm Hg and in diastolic blood pressure of 4-5 mm Hg;

  • ACE inhibitors achieved most of their power in reducing blood pressure at half of the maximum recommended dose, or less;

  • ARBs provide similar reductions in blood pressure compared with ACE inhibitors; and

  • There is no strong evidence that ACE inhibitors can prevent incident diabetes mellitus or heart failure.

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