Lowering serum uric acid concentrations is effective to control gout attacks and prevent formation of tophi. The objective of this retrospective cohort study was to describe patterns of persistence with and adherence to allopurinol treatment among gout patients, and explore determinants of non-persistence and non-adherence, using data from the clinical practice research datalink (CPRD) from the UK that were certified for valid data collection.
Patients 40 years or older with a first ever diagnosing coding for gout between 1st January 1987 – 30th June 2014 were included. Start of follow-up was the first prescription of allopurinol. Patients were excluded if they were (ever) users of febuxostat and probenecid or had a follow-up of less than 90-days after completion of the first prescription. Medication taking behaviour was described by non-persistence (occurrence of a first gap of 30 or 90 days) and non-adherence (proportion of days covered [PDC]) to allopurinol treatment.
Determinants included patient characteristics (at baseline), medication use (6 months prior to index-date) and other comorbidities (ever before index-date). Kaplan Meier survival and multivariable Cox- and logistic regression were used to estimate the median time until discontinuation, and the strength of the association between determinants with non-persistence (90-day gap) and non-adherence, respectively.
A total of 47.744 gout patients (76% men; mean age 64 yrs) received allopurinol exclusively. After 5.3 years (SD 4.6) of follow-up 77% had a gap of 30-days and 54% had a gap of 90-days, and were non-persistence. Median time until discontinuation was 229 days (CI 224 – 235) for a 30-day and 1059 days (CI 1012 – 1107) for a 90-day gap. The median PDC was 0.67 (IQR: 0.64). 61% of the patients were non-adherent (PDC<0.80). Females and current smokers have an increased risk on non-persistence and non-adherence, while older age, overweight, receiving anti-hypertensive or colchicine as well as suffering from dementia, depression, diabetes or dyslipidaemia decreased the risk of non-persistence and/or non-adherence.
Conclusion : this is the first large population based study in Europe which showed poor medication taking behaviour among gout patients initiating allopurinol. Females and current smokers have an increased risk, while an older age, overweight, receiving anti-hypertensives and suffering from certain comorbidities appear to decrease the risk of non-persistence and non-adherence.