Treatment of hypertension in the UK: simple as ABCD?

The measurement of blood pressure in primary care is a simple screening test to identify individuals at high risk of cardiovascular disease, including stroke. Hypertension is one of the most important preventable causes of premature morbidity and mortality¹ and a recent analysis of combined epidemiological data indicates that the relation between blood pressure and cardiovascular disease is much steeper than previously thought;² in other words, the potential benefits of intervention are higher. Allied to these impressive population data is a clinical-trials evidence base larger than any other in clinical medicine, pointing to the effectiveness of antihypertensive therapy in reducing cardiovascular risk.³ This evidence has provided the substrate for numerous guidelines on detection and treatment. The Chief Medical Officer for England has identified hypertension as one of his five priority areas, and the treatment of hypertension is a key target in National Service Frameworks for the prevention of coronary heart disease and stroke.

Although there are claims for drug-specific benefits, the effectiveness of antihypertensive therapy is most powerfully determined by the reduction in blood pressure achieved on treatment—i.e. by the quality of blood pressure control.^2,3 Yet, according to the Health Survey for England, the proportion of hypertensive patients who in 1998 achieved a blood pressure goal of <140/90 mmHg was only some 10%.⁴ The annual impact of this shortfall in treatment has been calculated by He and MacGregor⁵ as about 62 000 unnecessary deaths and 125 000 cardiovascular events that could have been prevented.

The study by Professor Walley and his colleagues reported in this issue (p. 525)⁶ is the largest retrospective survey of hypertension treatment yet conducted in the UK, involving over 20 000 patients treated in primary care. The findings are disturbing. After a minimum 4 years of follow-up, only 14% of patients on treatment had achieved the recommended blood pressure target. We might console ourselves with the hope that, since the patients began treatment in the mid-1990s, things will surely be much better today—but they are not. Importantly, the study provides insight into a key reason why blood pressure is so poorly controlled in UK patients—namely, the high rate of monotherapy. Over 65% of people with moderate to severe hypertension were treated with a single blood-pressure-lowering drug, whereas clinical trials have consistently demonstrated that the typical patient requires more than one drug to achieve good-quality control.⁷ The earlier Health Survey for England⁴ made a very similar observation: only one-third of patients treated for hypertension received more than one drug and less than 10% received more than two drugs. The ‘real world’ management of hypertension in the UK seems hard to defend when we consider the potential effectiveness of treatment.

What can be done to improve matters? If more than one drug is necessary to control blood pressure, then guidelines should offer specific advice on which drug combinations are likely to be complementary. In response, the British Hypertension Society (BHS) launched its ABCD algorithm, to provide more didactic advice on the sequencing of drugs.⁸ This algorithm is based on simple principles. The first is that younger people (<55 years) generally respond better to drugs that block the renin system—these include ‘A’ drugs (angiotensin converting-enzyme inhibitors or angiotensin receptor blockers) and ‘B’ drugs (β-blockers). In contrast, older people (>55 years) and black people respond better initially to ‘C’ drugs (calcium channel blockers) or ‘D’ drugs (diuretics). Second, for the majority who will require more than one drug, the logical strategy is to combine A or B with C or D; it is not logical at step 2 to combine A with B or C with D. The third step would involve triple therapy with either A+C+D or B+C+D. Where possible and when there is no cost disadvantage, at step 2 fixed-dose combinations would be appropriate to reduce the number of medications. This algorithm approach replicates the process adopted in clinical trials, which invariably achieve better blood-pressure control than real-world clinical practice. Whilst providing a template for rational prescribing it is not restrictive, in that it offers choice within a structured framework. Finally, the patient can be offered an individual treatment plan that sets out the objectives and the strategy required to reduce his or her blood pressure.

What is clear is that improvement on the very poor figures for blood-pressure control in the UK will not come from a new drug but rather from a sharper focus on implementation and process. To some in the medical profession, algorithms such as ABCD may seem simplistic and an affront to clinical freedom. I would ask, freedom to do what?—not enough, apparently. This aspect of public health strategy has been failing for too long and is too important to be left to chance.