REVIEW ARTICLE

PharmacoEconomics 2 (4): 324-334, 1992 1170-7690/92/00 I 0-0324/$05.50/0 © Adis International Limited. All rights reserved.

PECll20

Economic Factors in the Initiation of Antihypertensive Therapy

Ichiro Kawachi Channing Laboratory, The Department of Medicine, Harvard Medical School, Boston, Massachusetts, USA

Contents

324 325 325 326 326 326 327 328 328 328 329 33/ 33/ 332

Summary

Summary I. Overview of the Cost-Effectiveness of Hypertension Treatment 2. Improving the Cost-Effectiveness of Antihypertensive Therapy

2.1 Increasing the Effectiveness of Treatment 2.1.1 Importance of the Cut-Off BP Level for Initiating Treatment 2.1.2 Excluding 'White Coat' Hypertension 2.1.3 Priorities for Treatment 2.1.4 NonpharmacoIogicaI Therapy for Hypertension

2.2 Reducing the Costs of Treatment 2.2.1 Prescribing Low-Cost Initial Regimens 2.2.2 Choice of First-Line Therapy: The 'Cost-Quality Trade-Oft' 2.2.3 Choosing the Minimum Effective Dose 2.2.4 Step-Down Therapy

3. Conclusions

Optimal management of hypertension involves finding a balance among its benefits, risks and costs. Cost-effectiveness analysis helps to clarify not only the trade-offs between the costs and benefits of treatment, but also the trade-ofTs between the risks and benefits, and the costs and quality of therapy. Existing analyses of hypertension treatment suggest a consistent set of strategies by which cost-effectiveness may be improved. These include strategies to increase the effective­ness of therapy, such as excluding false-positive diagnoses of hypertension, and according higher priority to treating patients with sustained elevations of diastolic blood pressure above IOOmm Hg. A complementary set of strategies involve reducing the costs of therapy by prescribing lower­cost first-step regimens, making use of the minimum effective dose for particular medicines and attempting step-down therapy for suitable patients. Consideration of economic factors in initiating hypertension treatment is consistent with sound clinical practice.

Initiation of Antihypertensive Therapy

Several guidelines on the treatment of hyper­tension have been issued by expert groups (British Hypertension Working Party 1989; Joint National Committee 1988; Memorandum from a WHO/ISH Meeting 1989). These guidelines have tended to fo­cus on clinical criteria for initiating treatment; for example, using the patient's cardiovascular risk factor status as a basis for deciding the level of blood pressure (BP) at which to initiate drug treatment; or selecting a treatment regimen, based on the an­ticipated adverse effects of a BP-Iowering agent.

Few of these expert clinical guidelines, however, directly address the economic factors in initiating antihypertensive therapy. Consideration of cost-ef­fectiveness adds a new and important dimension to clinical decision-making. This review focuses on strategies to improve the cost-effectiveness of anti­hypertensive therapy.

1. Overview of the Cost-Effectiveness of Hypertension Treatment

It is generally accepted that treatment of mod­erate to severe hypertension [diastolic BP (DBP) of l04mm Hg and above] has clear-cut benefits and represents a cost-effective use of resources (Litten­berg et al. 1990). In contrast, the scientific contro­versy over the treatment of mild hypertension (de­fined as DBP 90 to 104mm Hg) continues in spite of a virtual cascade of editorials and reviews on the subject (Forrow et a1. 1988). The 'dilemma of mild hypertension' arises when the effectiveness of treatment is weighed against its costs and risks, the net outcome of which is found to be less obviously beneficial for patients with mild hypertension than for those with moderate or severe hypertension (Kawachi & Malcolm 1989a). In this situation, cost­effectiveness analysis helps to clarify the balance among the costs, risks and benefits of treatment.

Since the 1976 publication of Weinstein and Stason's landmark study of the cost-effectiveness of treating hypertension, several advances have oc­curred in the therapy for mild hypertension. Major clinical trials since 1976 have contributed infor­mation on the risks and benefits of treating mild hypertension (MacMahon et a1. 1986). A variety of

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new BP-Iowering agents have entered the market, offering greater benefits (in terms of quality of life) but at higher cost. These new developments have prompted a series of reappraisals of the cost-effec­tiveness of antihypertensive therapy (Edelson et al. 1990; Kawachi & Malcolm 1991; Littenberg et a1. 1990). While the different methods and assump­tions used in such studies tend to hamper the di­rect comparison of results (Johannesson & Jonsson 1991), a number of consistent findings have none­theless emerged.

The existing studies generally agree that the cost­effectiveness of treating mild hypertension im­proves with higher levels of pretreatment BP (Jo­hannesson & Jonsson 1992). Studies which took account of patients' quality of life (Edelson et al. 1990; Kawachi & Malcolm 1991; Weinstein & Sta­son 1976) indicate that for certain subgroups of patients at low risk of cardiovascular disease, anti­hypertensive therapy may result in only marginal (or even negative) changes in quality-adjusted life­years (QALYs). Priority should therefore be given to detecting and treating patients with a DBP of l00mm Hg or above (Beaglehole et a1. 1988; Sta­son 1989).

Wide variations have been noted in both the costs of antihypertensive regimens (Kawachi et a1. 1989) and their effects on patient quality of life (Croog et al. 1986). In the two studies which com­pared the cost-effectiveness of alternative regimens (Edelson et a1. 1990; Kawachi & Malcolm 1991), the existence of a cost-quality trade-off in anti­hypertensive therapy was noted. Initial monother­apy with ACE inhibitors - a regimen associated with comparatively few adverse effects and poten­tially a high quality of life (Croog et a1. 1986) -was found in both studies to be less cost-effective compared with the more traditional first-step reg­imens of diuretic (Kawachi & Malcolm 1991) or p-blocker therapy (Edelson et a1. 1990).

2. Improving the Cost-Effectiveness of Antihypertensive Therapy

Cost-effectiveness may be improved by reduc­ing the costs of treatment and/or increasing the ef­fectiveness of therapy. The framework by which

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Table I. Strategies for improving the cost-effectiveness of hypertension treatment (adapted from Stason 1989)

Increase effectiveness Initiate drug treatment only after verifying sustained blood pressure elevation

Exclude ·white coat' hypertension

Give higher priority to treating patients with diastolic blood pressure of 100mm Hg or above

Reduce costs Prescribing lower cost initial regimens

Reserve higher cost medicines for patients who fail to respond to lower cost medicines or who experience adverse effects

Use minimum effective doses

Try step-down therapy

one may consider the various strategies to improve the cost-effectiveness of treating hypertension is set forth in table I (adapted from Stason 1989).

2.1 Increasing the Effectiveness of Treatment

2.1.1 Importance of the Cut~Off BP Level for Initiating Treatment Wide variations have been noted in the level of

BP at which physicians in different countries ini­tiate drug treatment for hypertension (Weiland et al. 1991). For example, most practitioners in the US diagnose and treat hypertension soon after rec­ognition of a DBP above 90mm Hg (Bostick et al. 1991), whereas in Germany most practitioners treat at levels above loomm Hg (Weiland et al. 1991). Variations in management practices are even re­flected by the consensus guidelines issued by dif­ferent groups of experts; for example, the expert committee of the World Health Organization and the International Society of Hypertension (1989) recommends institution of drug therapy if the DBP is 95mm Hg or higher after 3 to 6 months of re­peated readings, whereas the guidelines issued by a working group of the British Hypertension Work­ing Party (1989) recommends that drug treatment is indicated only in patients aged under 80 years with DBP over 100mm Hg after 3 to 4 months.

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Even differences of 5 to 10mm Hg in the cut­off DBP for initiating drug treatment may have profound consequences for both the cost-effective­ness of therapy and the marginal costs of treating hypertension in the population. For example, in Sweden it has been estimated that lowering the cut­offDBP for treatment from 100 to 95mm Hg would increase the annual direct costs of treatment by £ltO million (Johannesson et al. 1991). It follows that the economic consequences of false-positive diag­nosis and over-treatment of raised BP may be sub­stantial. This has led to the recognition of the need for repeated measurements to verify the diagnosis of sustained BP elevations.

In the Australian National Blood Pressure Study, nearly half the people initially found to have DBP above 95mm Hg spontaneously dropped below 90mm Hg over the next 4 to 6 months (Manage­ment Committee of the Australian Therapeutic Trial in Mild Hypertension 1982). If drug treat­ment can be restricted to patients with sustained elevations in BP, the costs of treatment will be minimised at the population level, while the effec­tiveness of therapy for individual patients is en­hanced. Yet evidence from a Gallup survey in 1986 suggested that as many as 43% of physicians in the US commenced their patients on medication based on a DBP of 90 to 99mm Hg measured at a single office visit (quoted in Stason 1989). In a recent sur­vey of South Australian general practitioners, 32% revealed that they made the diagnosis of ' moderate hypertension' after measurements taken at 2 or fewer visits (Steven et al. 1992a). Thus, current medical practices in many countries probably tend to over-diagnose and over-treat 'hypertension', in spite of repeated recommendations by expert com­mittees to confirm the diagnosis of sustained BP elevation over 4 or more office visits (Kaplan 1992).

2.1.2 Excluding 'White Coat' Hypertension An additional cause of over-diagnosis is the

phenomenon of 'white coat' hypertension, in which about 20% of patients with persistently elevated of­fice readings have been found to be normotensive when multiple readings were obtained outside of the physicians' offices (Pickering et at. 1988). These

Initiation of Antihypertensive Therapy

patients do not require pharmacological treatment, even though they have 'sustained hypertension' as defined by expert guidelines. The 'white coat' phenomenon can be detected by the use of a semi­automatic home monitoring device (Evans et al. 1989); however, there have been no evaluations carried out to determine the cost-effectiveness of routinely using such devices in the screening and diagnosis of hypertension (American College of Physicians 1986; Reeves & Myers 1991).

2.1.3 Priorities for Treatment After the diagnosis of a sustained elevation in

BP has been verified, there still remains the ques­tion of the level at which to initiate pharmacolog­ical therapy. As described above, some guidelines recommend such treatment for all patients with DBP above 95mm Hg, while others set the cut-off level at or above l00mm Hg. Some authorities have argued for treating all patients with DBP above 90mm Hg (Gifford 1986; Moser 1988). The ra­tionale for recommending treatment for milder de­grees of hypertension (DBP lower than 95mm Hg) appears to be based on the finding that there is no natural threshold of BP below which there is no excess risk of cardiovascular disease. In a meta­analysis of 9 prospective observational studies, the risk of cardiovascular disease was positively and continuously associated with DBP throughout the range 70 to llOmm Hg (MacMahon et al. 1990). From a clinical and epidemiological viewpoint, therefore, the lower the level of BP, the lower the risk of cardiovascular disease (MacMahon et al. 1990), hence the desirability of treating even min­imally elevated BP. The problem with this view is that it ignores the economic dimensions of extend­ing treatment to low risk persons.

Cost-effectiveness analyses have repeatedly demonstrated that the lower the pretreatment BP, the lower the expected health benefits of treatment. The implications of this finding are 2-fold: first, among patients at low risk, the likelihood is in­creased that a small incremental health gain will be offset by an equally small but important risk of adverse effects of treatment (which include both the negative psychological impact of labelling the

327

patient as 'hypertensive', as well as the adverse ef­fects of medication). Secondly, as the cut-off level of BP is lowered, the cost-effectiveness of treating hypertension becomes progressively less favoura­ble compared with alternative uses of the same health resources.

With regard to the balance of risks and benefits, several studies have found that estimates of the net health gains of treating mild hypertension are highly sensitive to the quality of life reported during drug therapy (Edelson et al. 1990; Kawachi & Malcolm 1991; Weinstein & Stason 1976). For example, if a year of life while receiving any antihypertensive medication were equivalent to just 0.98 years of life without it, there would be no net health gain (as measured by QALYs) compared with no treat­ment, because the adverse effects of treatment would outweigh any gain in life expectancy (Edel­son et al. 1990; Kawachi & Malcolm 1991). Val­uing a year of life under medication at 0.98 of a year of 'normal' life is the equivalent of being pre­pared to forego 2% of a life-year (7.3 days) in order to avoid the adverse effects of the drug. If this re­flects the preferences of a real patient, then such patients are better off without treatment. It goes without saying that treatment for such patients would not be cost-effective.

If it is assumed that medication does not affect quality of life, then it is still necessary to ask whether the incremental benefits of treating pro­gressively milder degrees of hypertension are 'worth' the extra costs. For example, Kawachi and Mal­colm (1990) reported a cost-effectiveness ratio of $NZ43 2001 per QALY gained for treating a 40-year-old male with a DBP of llOmm Hg, whereas for a male with a DBP of 90mm Hg, the ratio was $NZ174700 per QALY gained (both figures dis­counted at 5%). For a 50-year-old male, the ratios were $NZ30 200 (DBP llOmm Hg), $NZ44 000 (DBP 100mm Hg) and $NZ66 000 (DBP 90mm Hg). These estimates may be compared to the cost­effectiveness ratios for other medical interventions such as coronary artery bypass surgery ($NZ6000

1 $NZI.OO = £0.29 = $U80.55 in August 1992.

328

to $30000 per QAL Y gained), renal dialysis ($NZ20 000 to $30000) and heart transplantation ($NZ20 000) [Kawachi & Malcolm 1990]. Given constrained resources, higher priority should there­fore be given to patients with a DBP of 100mm Hg or above (British Hypertension Working Party 1989; Hampton 1986; Sleight 1985).

2.1.4 Nonpharmacological Therapy for Hypertension As a result of the rising cost of antihypertensive

drugs and concern about adverse effects, there has been increasing interest in managing patients with­out medicines. The 3 best established nondrug therapies include weight reduction in the obese, dietary sodium restriction (80 to 125 mmoljday) for those who are salt sensitive and moderation of alcohol intake to no more than one ounce per day (Kaplan 1991). As examples of additional strate­gies, regular aerobic exercise (World Hypertension League 1991), maintenance of an adequate dietary intake of potassium, calcium and magnesium (Cut­ler & Brittain 1990; Kaplan 1991) and stress man­agement have variously been shown to lower BP safely.

Nondrug therapy is increasingly used in the context of step-down therapy (see below). Blaufox and associates (1984) and Langford et al. (1985) investigated whether weight reduction was effec­tive in the maintenance of normal BP once anti­hypertensive medication was withdrawn. In these studies, 60% of the patients placed on a weight loss regimen remained normotensive at 56 weeks com­pared with 35% of patients whose medication was withdrawn without dietary intervention.

Apart from having few adverse effects, nondrug therapies may result in health benefits additional to BP lowering. For example, weight reduction is associated with a fall in lipid levels, improved glu­cose tolerance and an improved sense of well-being (Oberman et al. 1990). In practice, however, long term compliance with nondrug regimens is be­lieved to be difficult to maintain, and there have been no randomised trials demonstrating the effi­cacy of nondrug therapy in lowering the incidence of hypertension-related disease (Millar & Waal-

PharmacoEconomics 2 (4) 1992

Manning 1992a). Finally, formal cost-effectiveness evaluations of non pharmacological therapies have yet to be carried out. Such analyses will need to take account of the costs of non pharmacological therapy, including the costs of joining weight re­duction programmes, maintaining a low-salt diet and increased frequency of visits to the clinic for BP monitoring.

2.2 Reducing the Costs of Treatment

2.2.1 Prescribing Low-Cost Initial Regimens Surveys of family practitioners have found wide

variations in the choice of initial therapy for hyper­tension (Kawachi et al. 1989; Steven et al. 1992b).The choice of drug can have a substantial impact on the cost and cost-effectiveness of therapy. In a survey of general practitioners' prescribing habits conducted within New Zealand in 1989, there was a greater than 12-fold variation in the average monthly costs of antihypertensive regi­mens, ranging from $NZ3.77 for monotherapy with thiazide diuretics to $NZ43.10 for ACE inhibitors and $NZ48.19 for calcium antagonists (Kawachi et al. 1989). Depending on the mix of drugs pre­scribed by the physician, the annual cost of treating a patient ranged from $NZ 12 to over $NZ580.

Similarly impressive variations in the costs of antihypertensive regimens have been reported in other countries (Baksaas 1984; Bergman 1987; Bock 1987; Hjort et al. 1984; Knorr et al. 1987; Steven et al. 1992a), where it has been concluded that the observed variations in prescription patterns essen­tially lack a rational explanation (Hjort et al. 1984), and appear to depend more on the therapeutic tra­ditions within countries (Bergman 1987) or the in­fluence of promotional activities by pharmaceuti­cal manufacturers (Knorr et al. 1987).

Following the entry of ACE inhibitors and cal­cium antagonists into the market, the costs of treating hypertension have increased rapidly (Bock 1987; Kawachi & Malcolm 1989b). In New Zea­land, the national inflation-adjusted expenditure on antihypertensive drugs increased by 61.7% between 1981 and 1987 (from $NZ21.4 million to $NZ34.6 million in constant 1981 dollars). During the same

Initiation of Antihypertensive Therapy

period, the number of patients receiving drug treat­ment remained virtually static, so that over 90% of the increased expenditure was attributable to the rise in the real cost of treatment. The increasing cost of treatment was in turn mostly due to 'mix' and 'entry' effects. The former refers to increases in the average cost of treating hypertension brought about by changes in the 'mix' of drugs prescribed; in particular, there was a marked decline in the market share of diuretics from 68.6% in 1981 to 47.1 % in 1987. By contrast, 'entry' effects refer to the introduction of newer, more expensive agents on the market - captopril and verapamil in 1983, nifedipine in 1985 and enalapril in 1986 - which contributed substantially to the rising cost of treat­ing hypertension. In New Zealand, the market shares of ACE inhibitors and calcium antagonists increased between 1981 and 1987 from 0% to 18.2% and 9.7%, respectively (Kawachi & Malcolm 1989b). Since 1987, other ACE inhibitors as well as second-generation a-blockers have entered the market. Equally dramatic changes in the choice of first-line therapy have been noted in other coun­tries (Bostick et al. 1991; Hurley et al. 1990; Knorr et al. 1987; Ray et al. 1986). In every case, the mar­ket share of ACE inhibitors and calcium antag­onists has gained at the expense of diuretics.

Following such trends, the question has been raised as to whether the new prescribing patterns constitute cost-effective clinical practice. In eco­nomic evaluations to date, the traditional diuretic/ ~-blocker regimens have been found to be more cost-effective than the newer agents (Edelson et al. 1990; Kawachi & Malcolm 1991). Edelson et al. (1990) compared the cost-effectiveness of various regimens to treat patients aged 35 to 64 years with DBP above 95mm Hg. The cost per year of life saved was $USlO 900 for propranolol, $US16 400 for hydrochlorothiazide, $US31 600 for nifedipine, $US61 900 for prazosin and $US72 100 for cap­topril (1987 US dollars, discounted at 5% per an­num). In the study by Kawachi and Malcolm (1991), the cost-effectiveness of treating a 50-year­old male with a DBP of llOmm Hg was $NZ7270 per QAL Y gained for thiazide diuretics, $NZ26 100 for ~-blockers and $NZ31 390 for ACE inhibitors

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($NZl.OO = approximately $USO.60 in 1988, 5% discounting).

2.2.2 Choice of First-Line Therapy: The 'Cost-Quality Trade-Off Quality of life is an important factor in making

comparisons of different regimens; for example, captopril appears to be associated with fewer ad­verse effects on quality of life compared with pro­pranolol (Croog et al. 1986). However, in the stud­ies to date, the incremental cost-effectiveness ratio for ACE inhibitors remained high compared with diuretics (Kawachi & Malcolm 1991) or ~-blockers (Edelson et al. 1990), even after reasonable as­sumptions were made to accommodate the degree to which ACE inhibitors 'improved' quality of life. For example, when Edelson et al. (1990) assumed that captopril had no adverse effect on health (i.e. a QALY equal to 1.0), while propranolol reduced the quality of life by 1 %, the incremental cost-ef­fectiveness of captopril over propranolol was $US 107 300 per additional QAL Y saved. If a year of life on propranolol was assumed to be equiva­lent to 0.995 of a year oflife without it (i.e. a 0.5% reduction in quality of life), then the incremental cost-effectiveness ratio of captopril over propran­olol rose to $USI 514700 per additional QALY saved. These results provide an indication of the magnitude of the 'cost-quality trade-offs' in anti­hypertensive therapy, originally described by Sta­son (1989).

A cost-effective strategy given the above find­ings would be to initiate hypertension treatment with lower-cost thiazide diuretics and ~-blockers. Individual patients may be still be suitable can­didates for first-line therapy with ACE inhibitors or calcium antagonists. For example, verapamil may be useful in hypertensive patients with coexi­sting angina, supraventricular arrhythmia or asthma (Millar & Waal-Manning 1992b), and ACE inhib­itors may be indicated in patients with congestive heart failure (Kaplan et al 1989). However, such individualised therapy is unlikely to explain the wide variations observed in actual clinical practice. For example, in the national survey of New Zea­land family doctors, the percentage of hypertensive

330

patients within a practice receiving ACE inhibitors ranged from zero to over 36% (Kawachi et al. 1989).

Thus, although the 1988 guidelines issued by the Joint National Committee endorse ACE inhibitors and calcium antagonists as appropriate choices for first-line therapy, there are sound economic rea­sons for continuing to use the traditional diuretic/ ,8-blocker regimens (Alderman 1992; Gifford & Borazanian 1989; Swales 1990; 1991). The most compelling reason is that a majority of patients do well on diuretic and ,8-blocker therapy, i.e. BP is controlled without sacrificing quality of life. In the Systolic Hypertension in the Elderly Program (SHEP), two-thirds of all participants were satis­factorily controlled on low-dose diuretics and ,8-blockers (SHEP Cooperative Research Group 1991). While it is possible that substituting an ACE inhibitor or calcium antagonist as the first drug of choice for all patients might achieve a marginal re­duction in unwanted adverse effects (Croog et al. 1986), such a strategy would deny the opportunity for cost-effective prescribing in the large majority of patients who would do well on either diuretics or ,8-blockers (Alderman 1992).

Apart from their effects on quality of life, con­cern has been expressed about the adverse meta­bolic effects of the traditional diuretic/,8-blocker first-step regimens (Swales 1991). It has been hy­pothesised that the disappointing failure to detect a statistically significant reduction in coronary dis­ease in the randomised trials of mild hypertension may have been due partly to the use of thiazide diuretics and ,8-blockers (MacMahon et al. 1986). However, there is meagre evidence to suggest that the adverse metabolic effects of traditional first-line regimens are quantitatively important. The study by Edelson et al. (1990) concluded that the BP-low­ering effect of a drug overwhelmed any effects it had upon serum cholesterol: the life years gained by each additional Imm Hg lowering of DBP was equivalent to the life years lost by raising the serum cholesterol level by 6%. From a meta-analysis of reports in the literature, hydrochlorothiazide was found to reduce DBP by an average 7.4mm Hg (for a person with pretreatment DBP of 95 to 104mm Hg), while causing the serum cholesterol level to

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Table II. Meta-analysis of the effects of antihypertensive agents on diastolic blood pressure (DBP) and serum cholesterol level (adapted from Edelson et al. 1990)

Drug Change in DBpe Change in serum (mm Hg) cholesterol (%)

Hydrochlorothiazide -7.4 +5.2 Nifedipine -10.0 -2.0 Captoprll -4.9 +1.3 Propranolol -9.8 -0.1

a For patients with initial DBP of 95 to 104mm Hg.

rise by an average 5.2% (Edelson et al. 1990). When these figures are compared with the antihyperten­sive and total cholesterol effects of newer drugs such as nifedipine and captopril, there does not appear to be a strong case for recommending the routine use of the newer agents as first-line therapy purely on the basis of their more favourable metabolic profile (table II).

In considering the economic consequences of choosing a first-line regimen, McCarron et al. (1984) found that diuretics, unlike a- and ,8-blockers, tended to induce more metabolic abnormalities, and hence necessitated more frequent supplemen­tal therapy and increased monitoring of clinical la­boratory tests. The authors concluded that the price advantage of thiazide diuretics over ,8-blockers was largely negated by the additional costs of supple­mental potassium therapy necessitated by the for­mer regimen (McCarron et al. 1984). On the other hand, even the extra costs of office visits, supple­mental medication and laboratory test monitoring are unlikely to obliterate the greater than II-fold difference in cost between diuretic monotherapy and ACE inhibitor (or calcium antagonist) mono­therapy (Kawachi et al. 1989).

Future studies may prove that the newer agents are superior to diuretics/,8-blockers in preventing coronary heart disease. However, based on the pre­sent state of evidence - which relies largely upon extrapolations from clinical studies using inter­mediate end-points - the beneficial effects of the newer regimens on coronary morbidity and mor­tality remain a matter of speculation (Alderman 1992; Gifford & Borazanian 1989; Swales 1990).

Initiation of Antihypertensive Therapy

2.2.3 Choosing the Minimum Effective Dose A further strategy to minimise the costs of anti­

hypertensive therapy without sacrificing the bene­fits is to use the minimum effective dose for an individual patient. The dose of many antihyper­tensive drugs is often less than the unit tablet size in marketed form. There are several precedents in the history of hypertension treatment where the in­itially recommended starting doses for a particular class of drugs - thiazide diuretics, (j-blockers and ACE inhibitors - turned out to be too high (Herx­heimer 1991). For example, captopril was mar­keted in 50 and 25mg tablets when first intro­duced. Following reports that the effective dose was often lower in patients (Veterans Administration Cooperative Study Group 1982), 12.5mg scored tablets were introduced in 1985 with a recommen­dation to begin treatment with a dose of 6.25mg.

The reason for the high doses seems to be that pharmaceutical manufacturers frequently market their products at doses that will be effective in around 90% of the target population (Herxheimer 1991). This apparently helps to convince physi­cians and regulatory authorities that the medicine is effective, thereby enhancing market penetration (Herxheimer 1991; Millar 1992). Ideally, pharma­ceutical manufacturers should be encouraged to market tablets containing less than the maximal effective dose - for example, by defining each mar­keted tablet size according to the proportion of patients responding to each dose. Dose levels set at ED20 and EDso could be marketed in addition to the ED90 (Herxheimer 1991; Kaplan 1992; Mil­lar 1992}.2 However, in the absence of doses de­fined in this way, it is still possible to determine the minimum effective dose for an individual patient via back titration (Maling & Kawachi 1990).

Randomised clinical trials to determine the minimum effective dose have been published for a variety of antihypertensive agents, including thiazide diuretics (Carlsen et al. 1990; McVeigh et al. 1988), ACE inhibitors (Veterans Administra­tion Cooperative Study Group 1982), and (j-block-

2 The EDso is the dose at which the drug is effective in SO% of patients.

331

ers (Maling & Kawachi 1990). According to a na­tional survey of New Zealand general practitioners (Kawachi et al. 1989), some (j-blockers are cur­rently prescribed for the treatment of hypertension at levels substantially exceeding the minimum ef­fective doses. For example, at least 25% of the patients in the survey (which included data on 1858 hypertensive patients) were being treated with doses of atenolol which were twice the established min­imum effective dose of 50 mgJday (Douglas-Jones & Cruickshank 1976; Jeffers et al. 1977). Similarly, the mean daily dose of propranolol in the survey was 106mg, whereas the established minimum ef­fective dose of propranolol is 80 mgjday (Serlin et al. 1980).

In a general practice-based study within New Zealand, 73 controlled and stable patients with hypertension were monitored for 3 months follow­ing a halving of their (j-blocker dosage (Maling & Kawachi 1990). In spite of the 50% reduction in dosage, there was no loss of antihypertensive effect at the end of the study.

These studies suggest that using the minimum effective dose by individual titration may lower the costs of therapy at no sacrifice to the patient in terms of BP control. A further benefit of back-ti­tration is the reduced chance of adverse effects. As Herxheimer noted: 'If one tablet contains the ED90 and no smaller size is made, then the therapeutic margin (the ratio between the toxic and the ther­apeutic dose - e.g. TDs/ED90) will be needlessly small for many patients, and this is usually un­desirable' (Herxheimer 1991). 3 By locating the minimum effective dose for an individual patient, it is possible to increase that therapeutic margin.

2.2.4 Step-Down Therapy A concept related to back-titration is the use of

step-down or discontinuation of antihypertensive therapy (Schmieder et al. 1991). A number of stud­ies have documented the potential for intermittent therapy or even complete discontinuation of therapy as an effective alternative to lifelong, con-

3 The TDs is the dose at which 5% of patients will experience toxicity.

332

tinuous medication. Broad selection criteria of can­didates for step-down therapy have been identified. Such candidates include patients with mild hyper­tension with I or more of the following character­istics: young age, normal bodyweight, low salt in­take, no alcohol consumption, low pretreatment BP, successful therapy with 1 drug only, and no or only minimal signs of end-organ damage (Schmieder et al. 1991).

Although the long term consequences for mor­bidity and mortality remain to be determined, step­down therapy appears to be safe for a period of several months to years. If successfully imple­mented, step-down therapy may result in savings in treatment costs, reduced adverse effects of cer­tain drugs, improved compliance with treatment, and hence improved cost-effectiveness of therapy.

3. Conclusions

Current management practices for the treat­ment of hypertension vary widely between physi­cians in different countries. Between individual physicians within any particular country, there are also wide variations in clinical practice, including the choice of a cut-off for initiating drug treatment and the selection of an initial regimen. The wide variations in practice may be attributable in part to the conflicting guidelines issued by different ex­pert committees.

To date, practice guidelines and protocols have tended to neglect the consideration of economic factors in initiating antihypertensive therapy. Cost­effectiveness analysis can help to clarify the trade­offs between the costs and benefits of treatment. The cost-effectiveness approach may be further ex­tended to quantify the trade-offs between the risks and benefits of treatment (using measures such as QAL Y s), as well as the cost-quality trade-offs in­volved in the choice of different therapeutic regi­mens.

Existing economic evaluations suggest a con­sistent set of strategies by which to improve the cost-effectiveness of hypertension treatment. They suggest that substantial opportunities exist for low­ering the costs of therapy, enhancing its effective-

PharmacoEconomics 2 (4) 1992

ness and reducing the variability of management practices. Consideration of cost-effectiveness ought to become an integral part of policy setting and treatment protocols.

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Correspondence and reprints: Dr Jchiro Kawachi. Channing Laboratory, 180 Longwood Avenue, Harvard Medical School, Boston, MA 02115, USA.

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