Clinical comparative trials of angiotensin II type 1 (AT1)-receptor blockers

Telmisartan or valsartan alone or in combination with hydrochlorothiazide: a review

The aim of this review was to compare telmisartan and valsartan in the treatment of hypertension. PubMed searches were conducted to identify randomized trials (n = 14) comparing the two agents, alone or combined with hydrochlorothiazide. With one exception, all studies with blood pressure reduction as primary endpoint showed significantly greater reductions with telmisartan than with valsartan. Other studies showed that telmisartan was associated with greater improvements in metabolic measures and inflammatory markers than valsartan. These findings suggest that pharmacologic differences between telmisartan and valsartan may translate into clinically relevant differences between the two drugs in the management of hypertension.

Candesartan and hydrochlorothiazide in isolated systolic hypertension

AIM

We investigated the efficacy and safety of daily candesartan 8/16mg and hydrochlorothiazide 12.5 mg as monotherapy and in combination in older patients with systolic hypertension.

METHODS

The study used a double-blind randomized placebo-controlled crossover design. Treatment phases were of 6 weeks duration. For inclusion, patients were aged 55-84 years with sitting systolic blood pressure (SBP) 160-210 mmHg and diastolic blood pressure (DBP) < 95 mmHg. Nineteen patients (11 male, eight female, median age 68 years) completed the study.

MAJOR FINDINGS

Compared with the placebo phase, clinic and ambulatory SBP was significantly reduced with both dose-adjusted candesartan and fixed-dose hydrochlorothiazide as monotherapy, the effect of candesartan being greater than that of hydrochlorothiazide. In combination, the effects of the two drugs were additive. Both drugs were well tolerated either as monotherapy or in combination.

CONCLUSION

Both candesartan and a low dose of hydrochlorothiazide are effective and well-tolerated antihypertensive agents in isolated systolic hypertension with additive effects in combination. Candesartan was more effective than hydrochlorothiazide, although it is possible that dose adjustment only of candesartan could have enhanced its relative effectiveness.

ACE-inhibitor, AT1-receptor-antagonist, or both? A clinical pharmacologist's perspective after publication of the results of ONTARGET

Clinical Pharmacology is commonly accepted to be a bridging discipline between basic science observations and clinical practice. Today, it should be a major task of the clinical pharmacologist in academia to provide support in the interpretation of preclinical and clinical study data, to develop evidence-based treatment guidelines and to serve as drug expert supporting all disciplines of clinical medicine with specific pharmacological and therapeutic knowledge. The results of the ONTARGET-trial confront both researchers and clinicians with the unexpected truth that AT(1)-receptor-blockade with an angiotensin-receptor-blocker (ARB) does not seem to have superior therapeutic benefit compared with an ACE-inhibitor (ACE-I) at reducing fatal and nonfatal cardiovascular events. The combination of the two drugs was associated with more adverse events without an increase in benefit. Therefore, the crucial question 'ACE-I, ARB, or both?' requires a new and critical appraisal depending on the medical indication for which these renin-angiotensin-system (RAS)-inhibitors are used: In a population of high-risk patients suffering from cardiovascular disease or diabetes mellitus, the evidence to favor an ARB over an ACE-I is still limited after ONTARGET and because of the higher costs for ARBs one can rather support the old therapeutic advice that ARBs are equally effective as ACE-Is and therefore therapeutic alternatives for patients with ACE-I intolerance. With respect to a very moderate additive BP-lowering effect of dual therapy with an ACE-I and an ARB seen in metaanalysis which was not even clearly attributable to dual RAS-inhibition and the increased adverse event rate in the combination treatment group of ONTARGET, this regimen seems not to be recommendable for the treatment of hypertension. Dual-RAS-blockade using an ACE-I-ARB-combination is an effective therapy to treat proteinuria and might be of therapeutic benefit especially in diabetic patients without concomitant diseases. There may be a therapeutic rationale to prefer ARBs over ACE-Is in well-selected patients with congestive heart failure (CHF) because a considerable amount of angiotensin II (Ang II) is produced independent of angiotensin-conversion-enzyme (ACE) in the failing heart and is therapeutically unaffected by ACE-I treatment. The results of the Val-HeFt and the CHARM-added-study revealed additive effects of an ARB on heart failure related morbidity and mortality when added to existing therapy with an ACE-I suggesting a role for ACE-I-ARB-combination treatment in well selected heart failure patients. Independent of the medical indication for its use, the concept of dual RAS-blockade with an ARB-ACE-I-combination should clinically be used with caution and a close monitoring of potassium levels and kidney function. Although the results of ONTARGET revealed equity of ramipril and telmisartan at reducing fatal and nonfatal cardiovascular events, we should not forget that pharmacologically not all ARBs are the same and the question if the study results of ONTARGET with telmisartan are transferable to the complete class of ARBs still merits further investigation.

Blood pressure-lowering efficacy of olmesartan relative to other angiotensin II receptor antagonists: an overview of randomized controlled studies

The aim of the present work was to review published studies investigating the dose-related efficacy on blood pressure (BP) of olmesartan and of other commercially available angiotensin II type I receptor blockers (ARBs). Patient population comprises mild to moderate hypertensive adult patients. We selected studies with comparable design and dose ranges. Dose-effect relationship plots were fitted for diastolic (DBP) and systolic (SBP) BP to the simplified E(max) model. We also examined controlled studies of olmesartan vs. other individual ARBs. Our overview was based on 7280 patients, of which 5769 received an ARB and 1511 received placebo. Except for losartan, the data fitted correctly to the E(max) model, with correlation coefficients ranging from 0.77 to 0.99. BP-lowering efficacy defined as E(max) was superior with olmesartan, (DBP/SBP mmHg: -9.0/-12.4) when compared with candesartan (-6.7/-11.3), irbesartan (-6.5/-11.2) and valsartan (-6.3/-8.9). Head-to-head comparisons of olmesartan to each of the other ARBs used at per-label 'recommended doses', support the finding of a greater BP-lowering effect of olmesartan. This overview suggests that clinically relevant differences in maximal efficacy, as well as in efficacy of per-label recommended doses can be evidenced among individual ARBs. Olmesartan efficacy was consistently at the highest end of the range of efficacy of ARBs studied.

Angiotensin receptor blockade in diabetic renal disease--focus on candesartan

Prevention and regression of diabetic renal disease can be obtained through the combination of strict blood pressure control, which frequently requires the combination of different antihypertensive drugs, with tight glycaemic control. Recent evidence obtained with the angiotensin receptor blockers has allowed the recognition by most guidelines that this class of agents constitutes the first choice to treat hypertension in type 2 diabetic patients presenting with diabetic renal disease at any stage of evolution, from microalbuminuria to advanced renal failure. Of course this must be accompanied by an integral coverture of the increased global cardiovascular risk that always accompanies this situation. This short review contains the most relevant evidence in favour of angiotensin receptor blockers, with particular emphasis on the capacities of candesartan for controlling blood pressure and protecting the kidney. In patients with type 2 diabetes and varying degrees of albuminuria, treatment with candesartan 8-32mg daily was shown to reduce urinary albumin excretion (UAE) by up to 60%. When given in addition to an ACE inhibitor (dual blockade), reductions in UAE of 25-35% relative to ACE inhibitor monotherapy have been found.

A placebo-controlled comparison of the efficacy and tolerability of candesartan cilexetil, 8 mg, and losartan, 50 mg, as monotherapy in patients with essential hypertension, using 36-h ambulatory blood pressure monitoring

This double-blind, randomised, controlled study compared the efficacy of candesartan cilexetil 8 mg (n = 87) and losartan 50 mg (n = 89), once daily for 6 weeks, relative to placebo (n = 80) in patients with mild-to-moderate essential hypertension (diastolic blood pressure (DBP): 95-115 mmHg). Ambulatory BP measurements were done every 15 min over 36 h. At the end of the 6-week treatment, the mean change in DBP between the baseline and the 0-24-h period after the last dose of study medication was greater in patients receiving candesartan cilexetil 8 mg (-7.3 mmHg +/- 6.9 mmHg) compared with losartan 50 mg (-5.1 mmHg +/- 4.9 mmHg) (p < 0.05) or placebo (0.3 mmHg +/- 6.5 mmHg) (p < 0.001). The mean change in systolic BP (SBP) during this time was greater in patients receiving candesartan cilexetil 8 mg (-10.8 mmHg +/- 11.3 mmHg), or losartan 50 mg (-8.8 mmHg +/- 8.9 mmHg) than placebo (1.2 mmHg +/- 9.9 mmHg) (p < 0.001). Candesartan cilexetil 8 mg was associated with a greater reduction in DBP and SBP, relative to placebo, when compared with losartan 50 mg, during both daytime and night-time, and between 12 and 24 h after dosing (p < 0.001). Both active treatments were well tolerated. In patients with mild-to-moderate essential hypertension, candesartan cilexetil 8 mg therefore had greater, more consistent antihypertensive efficacy throughout the day and the night, and long-lasting efficacy after the last dose, compared with losartan 50 mg. This greater efficacy is maintained with an excellent tolerability associated with members of the angiotensin Il type 1-receptor blocker class.

AT(1)-receptor blockers: differences that matter

The available angiotensin II type 1 (AT(1))-receptor blockers differ markedly in their pharmacological properties and clinical efficacy. Losartan shifts the dose-response curve for angiotensin II to the right without affecting the maximal response; this antagonism can be overcome by increasing concentrations of angiotensin II and thus losartan acts as a surmountable antagonist. By contrast, other agents suppress the maximal response to angiotensin II to varying extents; this can not be overcome by increasing angiotensin concentrations and hence these agents are insurmountable antagonists. Receptor binding studies have shown that candesartan has the highest affinity for the AT(1)-receptor, followed by irbesartan, valsartan and losartan, and that candesartan dissociates from the receptor more slowly than other antagonists. A meta-analysis using an E(Max) model has shown that differences in receptor binding activity are reflected in differences in maximal antihypertensive effect, and this finding is supported by the results of comparative clinical trials. Moreover, the prolonged binding of candesartan to the receptor is reflected in a longer duration of action, compared with losartan; the antihypertensive effect of candesartan persists for 48 h after dosing, compared with approximately 24 h with losartan. Candesartan thus offers extended therapeutic coverage, an important consideration since a majority of patients miss occasional doses of antihypertensive medication. There is currently no evidence that differences in receptor binding between AT(1)-receptor blockers translate into differences in tolerability. In summary, therefore, pharmacological differences between AT(1)-receptor blockers are reflected in clinically important differences in maximal antihypertensive effect, response rate, and duration of action.

Combination therapy with AT(1)-receptor blockers

Although current hypertension management guidelines recommend increasingly stringent blood pressure targets, these targets are seldom achieved in clinical practice. Even in patients with mild-to-moderate hypertension, monotherapy is only effective in approximately 50-70% of patients, and thus there is a clear need for combination therapy if stringent blood pressure targets are to be achieved. Drugs used in combination therapy should satisfy a number of prerequisites, including complementary mechanisms of action, enhanced efficacy in combination, and maintained (or improved) tolerability. Evidence is accumulating that combination therapy with an AT(1)-receptor blocker and a diuretic represents a rational and effective treatment option. In clinical trials, the combination of candesartan cilexetil, 16 mg, and hydrochlorothiazide, 12.5 mg, has been shown to be more effective in lowering blood pressure than either agent alone. Furthermore, this combination has been shown to reduce blood pressure to a greater extent, and control blood pressure in a higher proportion of patients, than the combination of losartan, 50 mg, and hydrochlorothiazide, 12.5 mg, both when used instead of or in addition to previous antihypertensive therapy. The placebo-like tolerability of AT(1)-receptor blockers was maintained when these drugs were used in combination with hydrochlorothiazide. The combination of candesartan and a dihydropyridine calcium antagonist has also been shown to be more effective than either component alone. Furthermore, in the Candesartan and Lisinopril Microalbuminuria (CALM) Study, the combination of candesartan and lisinopril reduced blood pressure to a greater extent than either agent alone, and tended to have a greater effect on microalbuminuria.

Current perspectives for AT(1)-receptor blockers in the management of heart failure

Despite improvements in therapy, long-term mortality remains high in patients with heart failure and thus there remains a need for new treatment strategies to reduce the burden of mortality and morbidity associated with this condition. AT(1)-receptor blockers represent a rational approach to the management of heart failure, and have been shown to have beneficial effects on heart failure symptoms and exercise tolerance. However, the two outcome trials reported to date have not shown conclusive evidence of improvements in mortality. The potential benefits of AT(1)-receptor blockers in heart failure are currently being investigated in several trials. The CHARM programme (Candesartan in Heart failure - Assessment of Reduction in Mortality and morbidity) is the largest heart failure trial so far. This comprises three trials: CHARM Alternative, in patients with left ventricular dysfunction who are intolerant to ACE inhibitors; CHARM Added, in patients with left ventricular dysfunction who are also receiving ACE inhibitors; CHARM Preserved, in patients with preserved left ventricular systolic function (ejection fraction >40%). The primary end point will be a composite of cardiovascular mortality and hospitalisation for the treatment of heart failure. Other trials are currently investigating the effects of AT(1)-receptor blockers when used as an alternative or in addition to ACE inhibitors. The CHARM programme, together with other studies, should clarify the role of these agents in the management of heart failure.