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Effectiveness of blood pressure-lowering drug treatment by levels of absolute risk: post hoc analysis of the Australian National Blood Pressure Study
  1. Chau Le Bao Ho1,
  2. Monique Breslin1,
  3. Jenny Doust2,
  4. Christopher M Reid3,4,
  5. Mark R Nelson1,4
  1. 1 Menzies Institute for Medical Research, University of Tasmania, Hobart, Tasmania, Australia
  2. 2 Faculty of Health Sciences and Medicine, Bond University, Gold Coast, Queensland, Australia
  3. 3 School of Public Health, Curtin University, Perth, Western Australia, Australia
  4. 4 CCRE Therapeutics, School of Public Health and Preventive Medicine, Monash University, Melbourne, Victoria, Australia
  1. Correspondence to Dr Chau Le Bao Ho; chau.ho{at}


Objectives In many current guidelines, blood pressure (BP)-lowering drug treatment for primary prevention of cardiovascular disease (CVD) is based on absolute risk. However, in clinical practice, therapeutic decisions are often based on BP levels alone. We sought to investigate which approach was superior by conducting a post hoc analysis of the Australian National Blood Pressure (ANBP) cohort, a seminal study establishing the efficacy of BP lowering in ‘mild hypertensive’ persons.

Design A post hoc subgroup analysis of the ANBP trial results by baseline absolute risk tertile.

Setting and participants 3244 participants aged 35–69 years in a community-based randomised placebo controlled trial of blood pressure-lowering medication.

Interventions Chlorothiazide500 mg versus placebo.

Primary outcome measures All-cause mortality and non-fatal events (non-fatal CVD, congestive cardiac failure, renal failure, hypertensive retinopathy or encephalopathy).

Results Treatment effects were assessed by HR, absolute risk reduction and number needed to treat. Participants had an average 5-year CVD risk in the intermediate range (10.5±6.5) with moderately elevated BP (mean 159/103 mmHg) and were middle aged (52±8 years). In a subgroup analysis, the relative effects (HR) and absolute effects (absolute risk reduction and number needed to treat) did not statistically differ across the three risk groups except for the absolute benefit in all-cause mortality (p for heterogeneity=0.04). With respect to absolute benefit, drug treatment significantly reduced the number of events in the high-risk group regarding any event with a number needed to treat of 18 (10 to 64), death from any cause with 45 (25 to 196) and major CVD events with 23 (12 to 193).

Conclusion Our analysis confirms that the benefit of treatment was substantial only in the high-risk tertile, reaffirming the rationale of treating elevated blood pressure in the setting of all risk factors rather than in isolation.

  • cardiovascular disease
  • antihypertensive drug
  • absolute cardiovascular risk
  • primary prevention
  • hypertension

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  • Contributors MRN is responsible for the study conception and data archive from the Australian Data Archive. CLBH performed the analysis and drafted the manuscript. MB, CMR and JD provided substantial support on statistical analyses. All authors made great contribution to the interpretation of data, critically revised the manuscript and approved the final version.

  • Funding The ANBP was supported by the National Health and Medical Research Council of Australia, the Life Insurance Medical Research Fund of Australia and New Zealand, the Victorian Government, the Clive and Vera Ramaciotti Foundations and the Raine Medical Research Foundation of Western Australia.

  • Competing interests CLBH is a PhD candidate at Menzies Institute for Medical Research; she has received a PhD scholarship from Merle Weaver Postgraduate Scholarship. JD is supported by National Health and Medical Research Council Screening and Test Evaluation Program Grant 633003. CMR is supported by a National Health and Medical Research Council Senior Research Fellowship (1045862). MRN has in the last 5 years served on an advisory board for AMGEN.

  • Patient consent Detail has been removed from this case description/these case descriptions to ensure anonymity. The editors and reviewers have seen the detailed information available and are satisfied that the information backs up the case the authors are making.

  • Ethics approval This study was approved by the Tasmanian Health and Medical Human Research Ethics Committee (H0015252).

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement No additional data are available.

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