Serum phosphorus levels and pill burden are inversely associated with adherence in patients on hemodialysis

BACKGROUND Phosphate binders (PBs) account for about one half of the daily pill burden for US hemodialysis (HD) patients, which may reduce adherence. Adherence can be estimated by the medication possession ratio (MPR), which is defined as the proportion of time a patient had sufficient medication to have taken it as prescribed. Gaps of time between prescription fills lower the patient's MPR. We assessed the association of PB pill burden and adherence (MPR) with phosphorus goal attainment. METHODS Using pharmacy management program data, HD patients on PB monotherapy were tracked from first PB fill during 1 January 2007-30 June 2011 for 1 year, or until PB change or censoring. Data were assessed with generalized linear models. RESULTS We analyzed 8616 patients. Higher pill burden was associated with lower adherence. Lower adherence tended to be associated with higher mean phosphorus levels and lower percentage of patients with serum phosphorus ≤5.5 mg/dL (P < 0.001). The association between adherence and these clinical outcomes was most pronounced in the lowest and highest pill burden strata (<3, >3-6, >12-15, >15). CONCLUSIONS Adherence, as measured by the MPR, was negatively related to higher pill burden and phosphorus levels and positively related to patients in the phosphorus target range. Within pill burden strata, phosphorus increased and patients in the target range generally decreased with decreasing adherence, suggesting that patients prescribed fewer PB pills are less likely to have treatment gaps, and may be more likely to achieve phosphorus targets.