Combination therapy as the initial drug treatment for hypertension: when is it appropriate?

An economic evaluation of antihypertensive therapies based on clinical trials

OBJECTIVE

Hypertension is a major issue in public health, and the financial costs associated with hypertension continue to increase. Cost-effectiveness studies focusing on antihypertensive drug combinations, however, have been scarce. The cost-effectiveness ratios of the traditional treatment (hydrochlorothiazide and atenolol) and the current treatment (losartan and amlodipine) were evaluated in patients with grade 1 or 2 hypertension (HT1-2). For patients with grade 3 hypertension (HT3), a third drug was added to the treatment combinations: enalapril was added to the traditional treatment, and hydrochlorothiazide was added to the current treatment.

METHODS

Hypertension treatment costs were estimated on the basis of the purchase prices of the antihypertensive medications, and effectiveness was measured as the reduction in systolic blood pressure and diastolic blood pressure (in mm Hg) at the end of a 12-month study period.

RESULTS

When the purchase price of the brand-name medication was used to calculate the cost, the traditional treatment presented a lower cost-effectiveness ratio [US$/mm Hg] than the current treatment in the HT1-2 group. In the HT3 group, however, there was no difference in cost-effectiveness ratio between the traditional treatment and the current treatment. The cost-effectiveness ratio differences between the treatment regimens maintained the same pattern when the purchase price of the lower-cost medication was used.

CONCLUSIONS

We conclude that the traditional treatment is more cost-effective (US$/mm Hg) than the current treatment in the HT1-2 group. There was no difference in cost-effectiveness between the traditional treatment and the current treatment for the HT3 group.

Combination therapy with ACE inhibitors/angiotensin II receptor antagonists and diuretics in hypertension

Essential hypertension is a very heterogeneous disease and different pressor mechanisms might interact to increase blood pressure. It is therefore not surprising that antihypertensive drugs, given as monotherapy, normalize blood pressure in only a fraction of hypertensive patients. This is, for instance, the case for diuretics, angiotensin converting enzyme (ACE) inhibitors and angiotensin II (AT1) receptor antagonists administered as single agents. The rationale for combining antihypertensive agents relates in part to the concept that the blood pressure-lowering effect may be enhanced when two classes are coadministered. Also, combination therapy serves to counteract counter-regulatory mechanisms that are triggered whenever pharmacologic intervention is initiated and that act to limit the efficacy of the antihypertensive medication. For example, the compensatory rise in renin secretion induced by sodium depletion may become the predominant factor sustaining high blood pressure. Simultaneous blockade of the renin-angiotensin system, with either an ACE inhibitor or an AT1-receptor blocker, makes this compensatory hyper-reninemia ineffective and allows maximum benefit from sodium depletion. The combination of a blocker of the renin-angiotensin system and a low dose of a diuretic increases the effectiveness, but not at the expense of tolerability compared with the individual components administered alone. Fixed-dose combinations containing an ACE inhibitor or an AT1-receptor blocker and a diuretic are therefore likely to become increasingly used not only as second-line therapy but also as first-line treatment.

Is fixed combination therapy appropriate for initial hypertension treatment?

Recent clinical trials in hypertension prove how seldom single drug therapy achieves target blood pressure (BP) and reduces cardiovascular morbidity and mortality. A natural response is the testing and marketing of fixed-dose combination products for hypertension, of which 14 have been approved in the United States since 1993. Currently, only five products are indicated by the Food and Drug Administration for initial therapy of hypertension; all include a diuretic. To achieve such an indication, studies must show not only safety and efficacy of the combination, but also BP lowering that is at least additive compared with the two agents given separately, as well as a "synergy" not present when each agent is given alone. Some advantages to initial combination therapy include greater BP reduction, improved adherence to pill taking, fewer side effects, and lower cost. The most likely candidates for initial combination therapy are patients with initial BP higher than 160/100 mm Hg, or those with a BP goal lower than the customary 140/90 mm Hg. These include patients with target organ damage, clinical cardiovascular disease, proteinuria, renal impairment, or diabetes mellitus. In many of these circumstances, an angiotensin converting enzyme inhibitor or angiotensin II receptor antagonist is frequently recommended; adding a diuretic or calcium antagonist to it is much more likely to result in achievement of the BP goal. More research is being done to explore the combination of not only two representatives from classes of conventional agents, but also other drugs that may help address the multiple manifestations of the "metabolic syndrome" that often accompanies hypertension.