Levodopa dosage determines adherence to long-acting dopamine agonists in Parkinson's disease

To test whether adherence to non-ergot, once-daily dopamine agonist (ODDA) therapy depends upon concomitant levodopa daily dose in Parkinson's disease (PD).

Consecutive levodopa-treated PD patients on ODDA therapy were invited to participate in the study. ODDA adherence was measured using subjective (Morisky-Green test, MGT) and objective (electronic monitoring of refill compliance, IANUS) methods. A combination of MGT and IANUS was used to define full (100%) adherence to ODDA therapy. Logistic regression methods were used to investigate the impact of levodopa daily dose on ODDA adherence after adjusting for relevant covariates.

Thirty-nine patients (19 men, 20 women; age, 70.2±8.9 years) were enrolled in the study. Twelve (31%) participants admitted to suboptimal ODDA compliance. Only 18 (46%) were estimated to be fully compliant. As expected, adherence was inversely related to levodopa daily dose. For every 100mg increase in levodopa dose, the risk to failure to adhere increased 1.86 times (95% CI, 1.21-3.74; p=0.0020). The covariate "total daily number of drugs" (not total daily number of pills) was also associated with worse adherence (p=0.0061). In contrast, patients who were initially treated with a dopamine agonist showed better ODDA adherence than those who were initially treated with levodopa (p=0.012). Levodopa doses greater than 600 mg/day were associated with suboptimal compliance.

In levodopa-treated PD patients, adherence to ODDA therapy is suboptimal and strongly associated with the levodopa daily dose and the total number of drugs used to treat patients' medical conditions.