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Plasma oxypurinol as a measure of adherence in clinical trials
  1. Lisa K Stamp1,
  2. Tony Merriman2,
  3. Christopher Frampton1,
  4. Mei Zhang1,3,
  5. Mary Wallace4,
  6. Jeffrey N Miner5,
  7. Nicola Dalbeth6
  1. 1Department of Medicine, University of Otago, Christchurch, Christchurch, New Zealand
  2. 2Department of Biochemistry, University of Otago, Dunedin, New Zealand
  3. 3Department of Toxicology, Canterbury Health Laboratories, Christchurch, New Zealand
  4. 4Deparment of Surgery, University of Otago, Dunedin, New Zealand
  5. 5Biology Department, Ardea Biosciences, Inc., San Diego, California, USA
  6. 6Deparment of Medicine, University of Auckland, Auckland, New Zealand
  1. Correspondence to Professor Lisa Stamp, Department of Medicine, University of Otago, Christchurch, P. O. Box 4345 Christchurch 8140, New Zealand; lisa.stamp{at}cdhb.health.nz

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Adherence to urate-lowering therapy (ULT) in people with gout is often poor. A recent systematic review revealed 10%–46% of people with gout adhere to treatment.1 Among chronic diseases, gout has particularly low adherence rates.2 Adherence in clinical trials of ULT is a particularly important issue, as the primary efficacy endpoint for most studies (including phase III studies that form the basis of regulatory approval) is the ability of the agent to reduce serum urate (SU). Pill count-based adherence ≥80% is frequently regarded as an appropriate cut-off for good adherence; however, this is an indirect measure. Measurement of drug concentration may be an improved measure of the adherence.3 The aim of this study was to establish the relationship between two different measures of adherence and SU endpoints in a clinical trial of allopurinol in gout.

Data, including demographics, SU, estimated glomerular filtration rate (eGFR), and plasma oxypurinol and allopurinol concentrations were available from a single study visit, and cumulative pill counts from the entire study period were available for 395 …

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