Assessment of adherence to cinacalcet by prescription refill rates in hemodialysis patients

Abstract

Secondary hyperparathyroidism is common among dialysis patients and leads to numerous complications including cardiovascular disease and renal osteodystrophy. Cinacalcet, an oral daily calcimimetic agent that sensitizes the calcium receptor to serum calcium, is approved for treatment of secondary hyperparathyroidism in dialysis patients. We identified 101 patients who received their first cinacalcet prescription between November 2004 and April 2005. All patients were participating in a Missouri state-funded pharmacy program providing free or low cost medications. We tracked the cinacalcet refill rate and refills for another control medication prescribed to each patient. The average cinacalcet refill rate over the first 12 months was 56% vs. 64% for the control medication (P=0.02). Good adherence, defined as >80% medication possession ratio over the 12 months, was 29% for cinacalcet and 33% for the control medication (P=0.68). Additionally, the refill rate for cinacalcet fell significantly over five quarterly periods from 53% in the first quarter to 37% in the 5th quarter. We conclude that dialysis patients' adherence to medications, including cinacalcet, is poor even when medications are provided at a nominal cost. Poor cinacalcet adherence would be expected to impair long-term control of SHPT. In a reimbursement system where injectable, but not oral medications, are bundled with dialysis payments there may be pressure to move patients to oral medications. The poor compliance found in this study highlights the potential adverse effects of movement toward self-administered oral therapy.