Original Research Article

PharmacoEconomics

, Volume 24, Issue 8, pp 767-781

First online:

Pharmacoeconomic Analyses of Azathioprine, Methotrexate and Prospective Pharmacogenetic Testing for the Management of Inflammatory Bowel Disease

  • Virginia L. PriestAffiliated withDepartment of Clinical Pharmacology, Christchurch HospitalDepartment of Pharmacology & Toxicology, University of Otago
  • , Evan J. BeggAffiliated withDepartment of Clinical Pharmacology, Christchurch HospitalDepartment of Medicine, Christchurch School of Medicine
  • , Sharon J. GardinerAffiliated withDepartment of Clinical Pharmacology, Christchurch HospitalDepartment of Medicine, Christchurch School of Medicine
  • , Christopher M. A. FramptonAffiliated withDepartment of Medicine, Christchurch School of Medicine
  • , Richard B. GearryAffiliated withDepartment of Medicine, Christchurch School of MedicineDepartment of Gastroenterology, Christchurch Hospital
  • , Murray L. BarclayAffiliated withDepartment of Clinical Pharmacology, Christchurch HospitalDepartment of Gastroenterology, Christchurch Hospital
  • , David W. J. ClarkAffiliated withDepartment of Pharmacology & Toxicology, University of OtagoIntensive Medicines Monitoring Programme, Pharmacovigilance Centre, Department of Preventive & Social Medicine, University of Otago
  • , Paul HansenAffiliated withDepartment of Economics, University of Otago

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Abstract

Objectives: To compare the cost effectiveness of azathioprine (AZA), methotrexate (MTX) and no immunosuppression for maintaining remission of moderate to severe inflammatory bowel disease (IBD) in New Zealand Caucasians, and to determine whether prospective testing for poor metabolisers of AZA by genotype or phenotype is cost effective.

Methods: Pharmacoeconomic models were developed to compare treatment costs and effects (QALYs) in theoretical populations of 1000 IBD patients over a 1-year period. Efficacy and tolerability profiles for AZA and MTX were taken from the literature. The costs (year 2004 values) of the drugs and treatment of adverse effects were estimated from New Zealand drug and service costs. Representations of the patients’ health-related quality of life (HR-QOL) were obtained from clinicians via the EQ-5D health state classification system and valued using the New Zealand EQ-5D social tariff. The effects of genotyping or phenotyping a population for thiopurine methyltransferase (TPMT) status were compared using the prevalence of TPMT deficiency in Caucasians, the relative risks of neutropenia and the associated costs.

Results: Net cost savings (vs no immunosuppressant treatment) of approximately $NZ2.5 million and $NZ1 million were realised for AZA and MTX, respectively, for the theoretical 1000 patients, and AZA generated 877 QALYs compared with 633 for MTX. Phenotype and genotype testing generated net cost savings (vs no testing) of $NZ120 000 and $NZ11 000, respectively. Savings related to phenotype tests were greater because of the lower assay costs of phenotype testing and a greater likelihood of pre-empting neutropenia.

Conclusion: Our model suggests that both MTX and AZA may generate significant net cost savings and benefits for patients with IBD in New Zealand, with AZA likely to be more cost effective than MTX. Prospective testing for poor metabolisers of AZA may also be cost effective, with phenotype testing likely to be more cost effective than genotype testing.