Abstract
Among patients with kidney stones rates of adherence to thiazide diuretics, alkali citrate therapy and allopurinol, collectively referred to as preventive pharmacological therapy, are low. This lack of adherence may reduce the effectiveness of secondary prevention efforts, leading to poorer clinical health outcomes in patients with kidney stones. To examine the impact that medication nonadherence has on the secondary prevention of kidney stones, we compared clinical health outcomes between patients who adhered to their regimen and those who did not.
Using medical and pharmacy claims data we identified adult patients with a physician coded diagnosis for kidney stones. Among the subset with a prescription fill for a preventive pharmacological therapy agent, we then measured adherence to therapy within the first 6 months of initiating treatment using the proportion of days covered formula. We defined adherence as a proportion of days covered value of 80% or greater. Finally, we fitted multivariable logistic regression models to examine the association between medication adherence and the occurrence of a stone related clinical health outcome (an emergency department visit, hospitalization or surgery for stone disease).
Of the 8,950 patients who met the study eligibility criteria slightly more than half (51.1%) were adherent to preventive pharmacological therapy. The frequency of emergency department visits, hospitalization and surgery for stone disease was significantly lower among adherent patients. After controlling for sociodemographic factors and the level of comorbid illness, patients who were adherent to therapy had 27% lower odds of an emergency department visit (OR 0.73, 95% CI 0.64-0.84), 41% lower odds of hospital admission (OR 0.59, 95% CI 0.49-0.71) and 23% lower odds of surgery for stone disease (OR 0.77, 95% CI 0.69-0.85) than nonadherent patients.
Our data highlight the consequences of nonadherence to preventive pharmacological therapy among patients with kidney stones. To improve adherence further research is needed to understand patient and provider level factors that contribute to lower rates of adherence.