Hypertension is a major risk factor for cardiovascular disease. Elevated blood pressure increases the risk of heart failure, stroke, coronary heart disease and renal disease.^1-3 Many trials have confirmed the benefit of pharmacological lowering of blood pressure on overall cerebrovascular and cardiovascular morbidity and mortality in middle aged and elderly subjects.^4-7

The detection and control of hypertension remains unsatisfactory. In Scotland, this decade, the percentages of hypertensive men and women not receiving satisfactory treatment are 75% and 58% respectively.⁸ Our challenge as clinicians is to ensure adequate blood pressure control while minimising side effects. Recent research has produced a range of more effective, more tolerable anti-hypertensives and all hypertensive patients can be treated to normotensive levels with available therapy. 

Early anti-hypertensive drugs (centrally acting alpha-agonists, vasodilators, ganglion blockers and potent sympathetic blockers) had numerous side effects and were poorly tolerated. They have been replaced by a large variety of new agents. The efficacy of thiazides and related diuretics in preventing most of the complications of hypertension has been conclusively demonstrated in long term controlled trials.^6,7,9 Beta-blockers also reduce the number of non-fatal strokes and probably coronary events, however, the latter is controversial as data is limited.^5,6,10 Any concerns about side-effects of diuretics and beta-blockers must be interpreted in this context. Morbidity and mortality data for ACE inhibitors, alpha-blockers and alpha/beta-blockers are unavailable so they have not been recommended as first line therapy. ACE inhibitors and probably AII antagonists have a special role in the treatment of patients with diabetic nephropathy and congestive heart failure. Recent long term clinical trials have documented decreased cardiovascular mortality and morbidity in hypertensive individuals treated with calcium channel blockers.^11,12 There is controversy regarding the use of short acting calcium channel blockers in patients with ischaemic heart disease.¹³ We await more definitive data. In the meantime, long acting formulations which do not stimulate the sympathetic nervous system are advisable in the treatment of hypertension as many of these individuals have occult coronary artery disease. 

Poor compliance

Lack of patient compliance is a common reason for treatment failure. Patients drop out of treatment because they may not fully understand that therapy will prevent further complications, especially when they currently feel well. They are not always aware that the drug or drugs may interfere with their quality of life, and they are not told that other drugs can be substituted which may be better tolerated.¹⁴ Physicians must include patient education as part of overall management. The availability of a variety of effective drugs with improved side effect profile gives us the ability to control hypertension without deterioration in the patient's quality of life, thus encouraging compliance with therapy. 

Combination therapy

There has been a recent increase in the use of combination therapy as we try to achieve lower levels of target blood pressure. Using a combination of drugs with complementary modes of action at sub maximal doses, means the incidence of dose dependant side effects decreases. At present, effective combinations are thiazides-beta-blockers, thiazides-ACE inhibitors, thiazide-Angiotensin II receptor blockers and calcium channel blockers-ACE inhibitors. Recent studies demonstrate that the combinations of low dose thiazide with ACE inhibitors or beta-blocker are effective and well tolerated and a rational alternative therapy in mild to moderate hypertension.^15,16 Likewise it has been shown that a Verapamil 240 mg - Enalapril 10 mg combination was significantly more effective at reducing BP than either drug alone and was not linked to a higher rate of adverse side effects.¹⁷ The decision to add instead of substituting medications depends on response to monotherapy. The major classes of antihypertensive drugs all control the blood pressure in about 50% of patients.¹⁸ In patients who respond (a BP reduction of 15/10 mmUg or more) but whose goal blood pressure is not reached, additive therapy is recommended. In contrast if monotherapy does not result in significant reduction in blood pressure substituting a different class of drugs is often necessary. 

Adequate control

Adequate management of hypertension means smooth blood pressure control over 24 hours. Inadequate control throughout the day is associated with end organ damage.¹⁹ The peak incidence of cardiovascular death which occurs in the early morning correlates with the rise in blood pressure at that period of the day. Many treated hypertensives may appear to have adequate blood pressure control based on post medication (peak) readings, however, by failing to consider the trough blood pressure readings, we miss patients with suboptimal early morning BP control. In the clinical setting where ambulatory BP monitoring is unavailable, adequate 24 hour control can be checked simply by asking the patient to omit their medication prior to an early morning visit.²⁰ It is advisable to use drugs with a half life that is adequate for 24 hour cover or a slow release formulation providing a relatively constant blood level and in a dose that has a similar effect at peak and trough levels.

One of the key remaining questions in the treatment of hypertension is what target blood pressure we should aim for. There is no consensus. Studies have suggested that lowering the diastolic pressure too far in certain patients with hypertension may provoke a myocardial infarction.^21,22 The opposing view is that preceding illness lowers blood pressure rather than that low blood pressure precipitates death from coronary hearth disease.²³ We await results of the Hypertension Optimal Treatment (HOT) study. The aim of the study is to establish target diastolic blood pressure for antihypertensive therapy which will produce the optimal reduction in cardiovascular mortality and morbidity. 

A patient-guided approach to choice of an antihypertensive agent is necessary, with better patient education and regular follow up. Diagnosis of hypertension is easy. Adequate control of hypertension is more difficult but certainly possible.

C Hart, 
Department of Clinical Pharmacology,
Sisters of Mercy Hospital,
Grenville Place,
Cork.

Department of Cardiology,
Cork University Hospital,
Wlton,
Cork.

References

1. Levy D, Wilson PWF, Anderson KM, Castelli WP. Stratifying the patient at risk from coronary. New insights from the Framingham Heart Study. Am Heart J 1990;119:712.
2. Kannel WB, Larson M. Long term epidemiological prediction of coronary disease. The Framingham experience. Cardiology 1993;82:137-52. 
3. Mc Mahon S, Peto R, Cutler J, Collins R, et al. Blood pressure, stroke and coronary heart disease. Part 1, prolonged differences in blood pressure:prospective observational studies corrected for the regression dilution bias. Lancet 1990;335:765-74.
4. Amery A, Birkenhanger WH, Brixco P, Bulpitt C, Clement D, Deruyttere M, et al. Morbidity and mortality results from the European Working Party on High Blood Pressure in the Elderly Tr