CURRENT ISSUES

Hypertension: APOR studies identify patients, outcomes and costs

- Matthew Nguyen-

A t the Second Annual International Meeting of the Association for Pharmacoeconomics andOutcomes Research [APOR; Philadelphia, US; April 1997] a session was held on the

identification of patients with hypertension and the costs and outcomes associated withantihypertensive therapies. The results of the studies presented below suggest the economicburden of hypertension is substantial, that there is room for improvement in antihypertensiveprescribing, and that appropriate use of such drugs can lead to better health outcomes andconsiderable cost savings.

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Cost of treating hypertension in Canada ...The direct cost of hypertension in Canada is

estimated to be ~ SCan1.3 billion, reported Rachel Taschand colleagues from Quebec and New Found1and,Canada.!

They used the Saskatchewan Health databases tocompare direct medical costs in a group of patientswith hypertension, compared with an age- and gender­matched control group. Univariate and multivariateregression analyses were performed using age, sex andcomorbid conditions to predict the cost of physicianvisits, prescription medications, hospitalisation andtotal treatment. The results were extrapolated from theSaskatchewan Health databases, using Canadianpopulation prevalence figures, to estimate the totalannual cost of treating hypertension in Canada.

... $Canl.3-2.8 billion/yearThe researchers concluded that the annual cost of

treatment for a patient with hypertension was $Can2040,compared with $Can1360 for a patient in the controlgroup. All differences in the cost of physician visits,prescription medications and hospitalisation werehighly statistically significant [see table].

Direct medical costs (SCan/patient)for patients with and without hypertension

Cost variables With hypertension WIthout hypertension

Physician visits 500 347

Prescription 599 256medications

Hospltalisations 940 756

After controlling for the presence of comorbidconditions along with age and gender, they found a$Can603 (adjusted) difference in the direct medicalcost for a patient with hypertension, compared with acontrol patient. The researchers concluded that theestimated annual incremental direct cost of treatinghypertension in Canada ranged from SCan1.3 billionto $Can2.8 billion, depending on assumptions intJrevalence. These figures, however, did not includethe costs of laboratory tests and procedures.

Comparing once-daily dihydropyridinecalcium antagonists

There may be an opportunity for cost savings inmanaging hypertension by using an extended-release(ER) formulation of nifedipine instead of amlodipine,

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according to W Linde-Zwirble and colleaguesfrom Health Process Management in Doylestown,Pennsylvania, US.2 They suggested that this isbecause of lower acquisition cost and lowerconcomitant drug therapy with the former agent.

Their study compared differences in healthcareencounters, resource use, total charges and drug chargesfor patients treated with either nifedipine ER oramlodipine. Adverse events and resource use weresimilar for both groups in the study.

Better outcomes with nifedipine ERHowever, the study authors noted a lower rate of

cardiovascular (CV) conditions (7.4 vs 14.6%,respectively) and hospitalisations (15.9 vs 23.4%) inpatients receiving nifedipine ER, compared withamlodipine. Also, patients treated with nifedipine ERreceived a significantly lower average number ofconcurrent antihypertensive agents than those receivingamlodipine (0.38 vs 0.52, respectively), whichcorrelated with a lower medication cost in the formertreatment group. This effect remained constant aftercontrolling for pre-existing conditions.

Aggressive antihypertensive therapy ofeconomic benefit

More aggressive antihypertensive therapy andrigorous adherence to hypertension guidelines can beexpected to reduce the risk of CV disease and relatedmortality, as well as yield considerable financialbenefits. This is the conclusion of US-based researcherswho presented an economic model of CV disease inpatients with hypertension.3

Their economic model addressed CV diseaseand its association with raised BP levels andantihypertensive therapy in the US adult population(aged 40-79 years). The model incorporated data fromthe Framingham Heart Study, major national healthsurveys and healthcare cost databases.

CV disease costs $US147o-2270 per capitaThe researchers estimated that 18% of US individuals

who are currently free of CV disease receive anti­hypertensives, while 17% of these antihypertensiverecipients continue to have diastolic BP levels of~ 90mm Hg. Each 10-point increase in diastolic BPamong antihypertensive recipients was associated with a23, 15 and 6% increase in the incidence of coronary

PhannacoEconomics & Outcomes News 7 Jun 1997 No. 115

4CURRENT ISSUES

Hypertension studies at APOR - continued

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heart disease, stroke and congestive heart failure,respectively.

Over a 5-year period, the expected per capita costof CV disease in antihypertensive recipients rangedfrom $US1470 at a diastolic BP of < 80mm Hg to$2270 at a diastolic BP of 90mm Hg.

Tool to identify patients at risk for ADRsIn another study, TJ Hudson and colleagues from

the University of Arkansas for Medical Sciences andPharmacy Associates in Little Rock, Arkansas, US,demonstrated how a retrospective database could beadvantageous for identifying patients at risk foradverse drug reactions (ADRs), as well as educatingphysicians about drug prescribing.4

The objective of their study was to determine theprevalence of hydrochlorothiazide (HCTZ) 50 mg/dayusing paid claims in a pharmacy benefit management(PBM) database. Of the 145000 individuals identifiedin the claims database, the study authors were able toidentify 340 who were dispensed HCTZ 50 mg/day(excluding patients with incomplete data). The studyauthors also sought to identify prescription claims forconcomitant medications for the treatment of metabolicdisturbances that could be negatively affected by theuse of thiazide diuretics.

Metabolic disorders in 31% of patientsThey found that 104 claims profiles (31 %) included

at least one medication for the treatment of metabolicdisorders in categories such as antidiabetic agents,antihyperlipidemic medications, potassium supple­ments and antigout medications. Physicians werenotified via a letter outlining the ceiling effect andmetabolic disturbances associated with high dosesof HCTZ.

The authors concluded that although some indivi­duals may respond favourably to HCTZ 50 mg/day,patients should be closely monitored for the presenceof new metabolic disturbances or worsening of knowndisorders.

Antihypertensives cost effective in the elderlyA Markov decision analysis conducted by investi­

gators from the University of Georgia, Athens, US,showed that drug therapy for hypertension is costeffective in the elderly, compared with other healthcareinterventions.5

Their decision tree modelled over a IS-year periodthe prognosis of an elderly individual (aged 60-75years) with hypertension. Estimated event rates forclinical endpoints (cerebrovascular, major coronary,and all other CV events) were obtained from9 randomised clinical trials of hypertension therapiesin individuals aged ~ 60 years.

The average expenditure on antihypertensives was$US428/patient/year. The average expenditures onhospitalisation for patients with and without a priordiagnosis on at least one of the clinical endpoints

PhaRT1acoEconomics & Outcomes News 7 Jun 1997 No. 115

totalled $US2I50 and $US4030 per patient per year,respectively. Over the IS-year period, the nondiscountedlife-expectancy among elderly patients with hyper­tension who were or were not receiving drug therapywas estimated to be 11.79 and 0.37 years, respectively.The average marginal cost-effectiveness ratio forantihypertensive therapy, compared with no suchtherapy, was $US2047Ilife-year gained.

Identifying a hypertensive cohortIF Murray and colleagues from US Quality

Algorithms in Blue Bell and Merck & Co. Inc., WestPoint, Pennsylvania, US, demonstrated how valuableadministrative data from a hospital or managed-care(MC) organisation can be, not only to characterise thepopulation in question, but also to extract informationthat may be useful in making sound medical decisions.6

The objective of this study was to develop andvalidate a selection algorithm for identifying patientswith hypertension in a large MC database. All patientswere identified using ICD-9-CM* codes specific forhypertension. Also, when available, any secondarycodes found on claims and pharmacy records wereused as corroborating evidence to help identify thiscohort. Validation of this technique was performedthrough a random sample chart audit of 174 patients.

Criteria for diagnosing hypertensionA diagnosis of hypertension was confirmed if any

of the following criteria were met:• hypertension recorded on a problem list• two separate recordings of systolic BP > 140mm Hg• two separate recordings of diastolic BP > 90mm Hg.

The study authors concluded that their algorithmwas highly accurate for identifying a hypertensivecohort using their administrative MC database with apositive predictive value of 90.2% which improved to95.4% when corroborating evidence of a diagnosiswas used.* ICD-9-CM = International Classification ofDisease, version 9,clinically modified1. Tasch RF, et aI. Cost of treatment of hypertension in Canada. AmericanJournal of Managed Care 3: S41-542, Mar 19972. Linde-Zwirble W. et a1.Comparison of two once-daily dihydropyridine CCBs in the management ofhypertension in PA Medicaid patients. American Journal of Managed Care3: 542, Mar 19973. Huse OM, et a1. An economic model of cardiovasculardisease in hypertensives receiving pharmacologic treatment. American Journalof Managed Care 3: 542, Mar 19974. Hudson TJ, et al. Pharmacy benefitmanagement databases can be used as a tool to identify patients at risk foradverse drug reactions. American Journal of Managed Care 3: 541, Mar1997 S. Ricci JF, et al. Meta-analysis, Markov decision tree, and cost­effectiveness analysis on the treaunent of essential hypertension in the elderly.American Journal of Managed Care 3: 542, Mar 1997 6. Murray JF, et a1.Utility and validation of administrative data for identifying a hypertensivecohort in a managed care population. American Journal of Managed Care 3:541. Mar 1997

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