Factors Influencing the Effectiveness of Allopurinol in Achieving and Sustaining Target Serum Urate in a US Veterans Affairs Gout Cohort

Objective. To assess factors associated with the ability to achieve and maintain target serum urate (SU) with allopurinol in patients with gout. Methods. We used US Veterans Affairs (VA) databases from 2002-2012. Eligible patients had >= 1 inpatient or >= 2 outpatient visits with a diagnostic code for gout, filled a new index allopurinol prescription, had at least 1 posttreatment SU level measured, and met the 12-month observability rule. Treatment successes were defined as the achievement of postindex SU < 6 mg/dl (success 1) and postindex SU < 6 mg/dl that was sustained (success 2). Results. Of the 198,839 unique patients with allopurinol use, 41,153 unique patients (with 47,072 episodes) and 17,402 unique patients (with 18,323 episodes) were eligible for analyses for success 1 and success 2; 42% each achieved (success 1) or achieved and maintained postindex SU < 6 mg/dl (success 2). In multivariable-adjusted models, factors associated with significantly higher odds of both outcomes were older age, normal body mass index, Deyo-Charlson index score of 0, rheumatologist as the main provider rather than non-rheumatologist, midwestern US location for the healthcare facility, a lower hospital bed size, military service connection for medical conditions of 50% or more (a measure of healthcare access priority), longer distance to the nearest VA facility, and lower preindex SU. Conclusion. We identified novel factors associated with maintaining SU < 6 mg/dl based on a theoretical model. Several potentially modifiable factors can be targeted by individual/provider/ systems interventions for improving successful achievement and maintenance of target SU in patients with gout.