Background/Purpose: Higher serum uric acid levels in gout patients have been associated with an increased frequency and risk of gout flares and greater subsequent healthcare costs. Despite the wide availability of allopurinol, achieving a therapeutic serum uric acid (sUA) level remains problematic for clinicians and patients. The objectives of this study included identifying predictors of an sUA response to allopurinol and investigating the associated healthcare costs.

Methods: A retrospective cohort study of a large health benefits company was conducted among Medicare Advantage Prescription Drug (MAPD) plan patients with gout newly initiated on allopurinol between 1/1/08 and 12/31/10. Patients were separated into two cohorts defined by their sUA response to allopurinol (sUA < 6 mg/dL or sUA > 6 mg/dL). Mean allopurinol adherence, as measured by proportion of days covered (PDC), was reported at 12 months follow-up. Multivariate logistic regression was used to determine factors associated with allopurinol response. A generalized linear model was developed to assess the association between allopurinol response and total healthcare costs.

Results: Of the 2,703 patients initiated on allopurinol, 57% had a baseline sUA and 33% had sUA ≤ 6 mg/dL in the follow-up period. Higher adherence was associated with achieving an sUA < 6 mg/dL compared to > 6 mg/dL (PDC=0.74 and 0.59, respectively, p<.0001). Predictors of sUA < 6 mg/dL included female sex, higher allopurinol PDC, and allopurinol dose  >100 mg/day (OR:1.74, CI:1.41-2.13; OR:12.28, CI:8.25-18.28; OR:5.84, CI:4.73-7.20, respectively). Hispanic ethnicity, higher baseline sUA, renal impairment (Stage 3 vs. Stage 1), colchicine use, and NSAID use were associated with lower odds of responding to allopurinol therapy (OR:0.32, CI:0.14-0.76; OR:0.60, CI:0.56-0.66; OR:0.41, CI:0.30-0.55; OR:0.79, CI:0.65-0.97; OR:0.68, CI:0.55-0.85, respectively). There were no significant differences in total healthcare costs between the two cohorts.

Conclusion: A large percentage of patients initiated on allopurinol did not have adequate sUA monitoring, and did not achieve an sUA < 6 mg/dL. Drivers of a therapeutic response included increased adherence and dose escalation. This study demonstrates that ample opportunity exists for clinicians and patients to improve sUA monitoring and treatment adherence when initiating urate lowering therapy.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/evaluating-allopurinol-therapy-and-serum-uric-acid-levels-in-medicare-beneficiaries-with-gout/