Allopurinol is used as long-term therapy to reduce the occurrence of gout flares. This study estimated the impact of patient adherence to allopurinol on hyperuricaemia (serum uric acid levels, sUA > 6 mg/dl) and the identification of non-adherence predictors.
The Italian Health Search-CSD Longitudinal Patient Database was accessed to identify outpatients aged ≥ 18 years with gout and prescribed with allopurinol during the years 2002-2011. Patients with a proportion of days covered ≥ 80% were considered adherent to allopurinol. Data on sUA levels over the first year of therapy were categorised in three time-windows (30-89; 90-149; 150-365 days). Logistic regressions were used to estimate the association between adherence and hyperuricaemia, as well as non-adherence predictors.
A total of 3727 patients were included. In the interval 0-29 days, the proportion of patients adherent to allopurinol was 45.9%, while up to 89, 149 and 365 days the percentages were 16.7%, 10.0% and 3.2%, respectively. The proportions of hyperuricaemic patients for each time-window were 43.1%, 42.4%, 32.6% and 59.0%, 64.0%, 66.4% among adherent and non-adherent patients, respectively. In the multivariable analysis, adherence was associated with a significant lower risk of hyperuricaemia. The adjusted ORs were 0.49 (95% CI: 0.33-0.73), 0.40 (95% CI: 0.24-0.67) and 0.23 (95% CI: 0.15-0.34) for the first, second and third time-window, respectively. Patients with hypertension (adjusted OR = 0.64, 95% CI: 0.42-0.99) and history of gout flares (adjusted OR = 0.55, 95% CI: 0.32-0.95) were significantly adherent to allopurinol.
Adherence monitoring in patients with gout is pivotal to ensure the effectiveness of therapy. To gain a better patient adherence, the communication between physicians and patients should be improved.