Estimation of adherence to urate‐lowering therapy in people living with gout using Australia's Pharmaceutical Benefits Scheme and patient‐reported dosing

Aims The aim of this study was to estimate adherence to urate‐lowering therapy (ULT), predominately allopurinol, from Australia's Pharmaceutical Benefits Scheme (PBS) claims database in association with (1) patient‐reported doses and (2) World Health Organization's (WHO) defined daily doses (DDD), namely, allopurinol (400 mg/day) or febuxostat (80 mg/day). Methods Proportion of days covered (PDC) was calculated in 108 Gout App (Gout APP) trial participants with at least two recorded ULT dispensings in an approximately 12‐month period before provision of intervention or control apps. Adherence was defined as PDC ≥80%. We measured the correlation between the two methods of calculating PDC using a Wilcoxon signed rank test. Agreement between ULT‐taking status (self‐reports) and ULT‐dispensed status (PBS records) was tested with Cohen's kappa (κ), and positive and negative percent agreement. Results Allopurinol was prescribed in 93.5% of participants taking ULT. Their self‐reported mean daily dose (SD) was 291 (167) mg/day. Mean PDC (SD) for allopurinol was 83% (21%) calculated using self‐reported dose, and 63% (24%) using WHO's DDD. Sixty‐three percent of allopurinol users were identified as adherent (PDC ≥80%) using self‐reported dose. There was good agreement between self‐reported ULT use and PBS dispensing claims (κ = 0.708, P