Factors Associated With Preventive Pharmacological Therapy Adherence Among Patients With Kidney Stones

To determine adherence patterns for thiazide diuretics, alkali citrate therapy, and allopurinol, collectively referred to as preventive pharmacological therapy (PPT), among patients with kidney stones.

Using medical claims data, we identified adults diagnosed with kidney stones between 2002 and 2006. Through National Drug Codes, we determined those with one or more prescription fills for a PPT agent. We measured adherence to PPT (as determined by the proportion of days covered formula) within the first 6 months of starting therapy and performed multivariate analysis to evaluate patient factors associated with PPT adherence.

Among 7980 adults with kidney stones who were prescribed PPT, less than one third (30.2%) were adherent to their regimen (indicated by proportion of days covered  ≥ 80%). Among those on monotherapy, rates of adherence differed by the type of PPT agent prescribed: 42.5% for thiazides, 40.0% for allopurinol, and 13.4% for citrate therapy. Factors that were independently associated with lower odds of PPT adherence included combination therapy receipt, female gender, less generous health insurance, and residence in the South or Northeast. In contrast, older patients and those with salaried employment had a higher probability of PPT adherence.

Adherence to PPT is low. These findings help providers identify patients where PPT adherence will be problematic. Moreover, they suggest possible targets for quality improvement efforts in the secondary prevention of kidney stones.