INCREASED INCIDENCE OF LEVODOPA THERAPY FOLLOWING METOCLOPRAMIDE USE

Objective.-To determine whether there is an increase in use of antiparkinsonian therapy in older persons taking metoclopramide hydrochloride. Design.-Case-control study. Setting.-New Jersey Medicaid program. Patients.-Medicaid enrollees aged 65 years and older. Cases were patients newly prescribed a levodopa-containing medication (n=1253); a secondary case group were patients newly prescribed an anticholinergic antiparkinsonian drug (n=2377). The control group consisted of 16 435 Medicaid enrollees older than 65 years who were not users of any antiparkinsonian therapy. Main Outcome Measures.-We used logistic regression to determine the odds ratio (OR) for the initiation of antiparkinsonian therapy in patients using metoclopramide relative to nonusers, after adjusting for age, sex, race, nursing home residence, exposure to antipsychotic medication, and days hospitalized. Results.-Metoclopramide users were three times more likely to begin use of a levodopa-containing medication compared with nonusers (OR=3.09; 95% confidence interval [CI], 2.25 to 4.26). Risk increased with increasing daily metoclopramide dose: the OR was 1.19 (95% CI, 0.50 to 2.81) for more than 0 to 10 mg per day, 3.33 (95% CI, 1.98 to 5.58) for more than 10 to 20 mg per day, and 5.25 (95% CI, 1.16 to 8.50) for more than 20 mg per day. The effect persisted after adjustment for demographic, health service utilization, and medication use variables. The OR for initiation of anticholinergic antiparkinsonian drugs was also elevated in metoclopramide users. Conclusion.-Metoclopramide use confers an increased risk for the initiation of treatment generally reserved for the management of idiopathic Parkinson's disease. Such polypharmacy may represent the misdiagnosis of Parkinson's disease in patients with drug-induced parkinsonian symptoms, which should be ruled out before starting dopaminergic therapy for this condition.