Background: Patient adherence limits the effectiveness of preventive pharmacologic therapy (PPT) for urinary stone disease (USD), highlighting the need for accurate adherence monitoring. We assessed associations between potassium citrate adherence measures, changes in 24-hour urine parameters, and the risk of recurrent stone events. Methods: In this retrospective cohort study, we identified adults enrolled in Medicare with USD, a baseline 24-hour urine collection (2010-2019), hypocitraturia or low urine pH, a prescription for potassium citrate monotherapy, and a follow-up urine collection. We defined two adherence measures: (1) percentage of days covered (PDC) using pharmacy claims and (2) change in urinary potassium between baseline and follow-up divided by medication dose (ΔK/dose). We assessed the association of these measures with changes in urinary citrate and pH using analysis of covariance, and the association between adherence and recurrent stone events using Cox models. Results: Among 793 patients meeting study criteria, 504 (63.6%) were adherent based on pharmacy claims (PDC≥80%) and 389 (49.1%) based on ΔK/dose≥0.5. Compared to PDC≥80%, ΔK/dose≥0.5 had a stronger association with change in urinary citrate ( p <0.001) and pH ( p <0.001). Compared to PDC≥80%, patients with PDC<80% had a higher risk of recurrent stone events (hazard ratio HR 1.431; 95% confidence interval CI, 1.049-1.952), whereas ΔK/dose was not statistically significantly associated with recurrent stone events (HR 1.032; 95% CI, 0.740-1.439). Conclusions: There are clinically meaningful differences in potassium citrate adherence measures. ΔK/dose was more strongly associated with the change in urinary citrate and pH. However, only PDC was significantly associated with recurrent stone events.
Ennis et al. (Tue,) studied this question.