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The Pharmaceutical Journal Vol 265 No 7114 September 16, 2000
Pharmacy Practice Research
Papers presented at the British Pharmaceutical Conference, Birmingham, September 10 to 13, 2000 pR14

Encouraging rational prescribing of antihypertensive combinations in primary care through formulary and prescribing protocol development

By I. T. S. Cunningham, V. McKenzie and G. Cunningham*

Introduction New evidence on the treatment of hypertension has been summarised in recent British Hypertension Society guidelines.1 These include evidence that optimal blood pressure (BP) targets are currently set too high and need to be lowered, the control of hypertension in the United Kingdom still remains suboptimal, and the majority of patients require combinations of antihypertensives to achieve optimal control.
Antihypertensive drugs should be prescribed in rational (or logical) combinations. This is exemplified in the Cambridge AB/CD rule,2 which states that a drug should be selected from either A (angiotension converting enzyme inhibitor) or B (beta-blocker) and combined with either C (calcium antagonist) or D (diuretic). In view of this, a prescribing protocol was incorporated into the practice formulary. The objective of this study was to determine the extent to which rational combinations were being used in the practice following introduction of the formulary and prescribing protocol.

Methods The study was carried out in an eight-GP, 12,500-patient practice in a suburban location south of Aberdeen. All patients with hypertension were identified from the practice computer. For each the drug record was checked to identify patients on combinations of antihypertensive drugs. The notes of such patients were then screened using a prepiloted data collection form for unit number, date of birth, sex, GP, consultant (if relevant), previous medical history, current medication including drug, dose, dose frequency, history of antihypertensives prescribed, and history of BP measurement.

Focal points

  • New evidence indicates that lower blood pressure targets are desirable and therefore all treatment modalities for hypertension must be optimised
  • To optimise drug therapy, different antihypertensive drugs should be used in combinations that are logical
  • In the practice studied, 30 per cent of hypertensives were on combination therapy and only 4.1 per cent were shown to be on combinations that were considered less logical
  • Further work is required to determine whether the high use of monotherapy in this practice is justified
  • Formulary and prescribing protocol development should contribute to the rational use of combinations of antihypertensives in primary care

Results Of 386 patients with a diagnosis of hypertension, 116 (30 per cent) were on a combination. Fifty-nine (50.8 per cent) were male and the median age of the cohort was 64 years. Only 16 patients were on less logical combinations of drugs, and 83 of the remaining patients were on a two-drug rational combination which included: B and D (32); A and D (24); B and C (13); A and C (9); fixed dose combinations, eg, Tenoret-50 (3); and two patients on an alpha-blocker plus a beta-blocker and a diuretic plus methyldopa. Combinations using three drugs were used in 17 patients. These included: BCD (8 patients); ACD (3 patients); ABC (3 patients); and ABD (3 patients). No guidelines exist for the rationality of triple therapy combinations. Figure 1 shows details of the 16 patients on two-drug less logical combinations.
Twelve (54.5 per cent) of the patients on less logical combinations had co-morbid disease states; however, none had valid influence over the choice of antihypertensive.

Figure 1
Figure 1. Patients on less logical combinations of antihypertensives and BP control

Discussion This study shows that a minority (30 per cent) of all hypertensives in the practice received a combination regimen and only 4.1 per cent were on a less logical combination, which may be a consequence of the formulary and protocol. However, 45 per cent of patients on less logical combinations had a suboptimal BP at the old 160/ 90mmHg level which the GPs were following at the time.
It has been estimated that up to two thirds of hypertensives require combinations,3 but there is also evidence that crossover rotation over the four major drug classes can increase the success rate of monotherapy to as high as 73 per cent. Further work is required to determine whether the high use of monotherapy in this practice is justified. With the introduction of the new stricter BHS guidelines1 it is more important than ever that every available treatment modality is optimised. To this end it is imperative that pharmacological therapy should include the use of combinations of antihypertensives that are rational.

School of pharmacy, Robert Gordon university, Aberdeen; *Grampian Primary Care NHS trust, Aberdeen

References

1. Ramsay LE, Williams B et al. Guidelines for the management of hypertension. Report of third working party of the British Hypertension Society. J Human Hypertension 1999;13:569-92.
2. Dickerson JEC, Hingorani AD et al. Optimisation of anti-hypertensive treatment by crossover rotation of four major classes. Lancet 1999;353:2008-13.
3. Hansson L et al, for the HOT study group. Effects of intensive blood-pressure lowering and low-dose aspirin in patients with hypertension. Principle results of the hypertension optimal treatment (HOT) randomised trial. Lancet 1998;351:1755-62.