Prevalence and cost of medication nonadherence in Parkinson's disease: evidence from administrative claims data.

We estimated the prevalence of medication nonadherence in Parkinson's disease (PD) and the association between treatment nonadherence and healthcare costs. Insurance claims from over 30 US health plans were analyzed. Inclusion criteria were as follows: PD diagnosis, >or=1 PD-related prescription between 1/1/1997 and 12/31/2004, continuous health plan enrollment for >or=6 months before and >or=12 months after first PD prescription. Adherence, all-cause healthcare utilization, and all-cause costs were evaluated over 12 months post-treatment initiation. Adherence was measured using the medication possession ratio (MPR), with MPR < 0.8 defining nonadherence. Among patients identified for inclusion (N = 3,119), 58% were male and mean age was 69 years. Mean MPR was 0.58 and 61% of patients were nonadherent. Unadjusted mean medical costs were significantly higher (P < 0.01) among nonadherers ($15,826) compared with adherers ($9,228), although nonadherers had lower prescription drug costs ($2,684 vs. $3,854; P < 0.05). After controlling for confounders in multivariable analyses, a large positive relationship between nonadherence and both medical and total healthcare costs remained (+$3,451, P < 0.0001 and +$2,383, P = 0.0053, respectively). Medication adherence in PD is suboptimal and nonadherence may be associated with increased healthcare costs despite offsets from reduced drug intake. Efforts to promote medication adherence in PD may lead to cost savings for managed care systems.