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A Double-blind Clinical Trial

John G. Nutt, MD; Julie H. Carter, ANP; Nichole E. Carlson, PhD

Arch Neurol. 2007;64(3):319-323.

Objective  To determine if repeated dosing with methylphenidate hydrochloride (MPD) (Ritalin; Novartis Pharmaceuticals, East Hanover, NJ), an inhibitor of the dopamine transporter, would augment the effects of oral levodopa in patients with Parkinson disease.

Design  The study was a double-blind, randomized, placebo-controlled crossover trial.

Setting  The trial was conducted at the General Clinical Research Center (GCRC) as an inpatient study.

Subjects  Thirteen people with idiopathic Parkinson disease and a fluctuating motor response to levodopa were recruited from movement disorder clinics as a convenience sample. One subject was excluded because he did not have a 10% increase in tapping speed in response to levodopa. The remaining 12 subjects completed the protocol.

Interventions  A 0.4-mg/kg dose of MPD was administered orally at 8 AM, noon, and 4 PM in conjunction with the subjects' normal oral antiparkinsonian medications. Oral levodopa dosage was decreased as clinically feasible during the first 4 days in the GCRC during open-label administration of MPD and hourly monitoring of parkinsonism and vital signs between 7 AM and 8 PM. Subjects were discharged taking their usual antiparkinsonian medications without MPD. They returned 1 and 2 weeks later to the GCRC for 1 day of hourly monitoring of their response to the medication regimen derived during the 4 days in the GCRC, once with MPD and once with identical-appearing placebo, in a randomized sequence and double-blind conditions.

Main Outcome Measures  The main outcome measure was the duration of "on" time between 9 AM and 8 PM measured by an increase in tapping speed by 10% over the average of the 7 AM to 8 AM predosing tapping speed measurements. Secondary measures were estimates of "on" time obtained with the timed walking task, tremor scores, and dyskinesia scores. In addition, averages of hourly tapping speeds, walking speed, tremor scores, dyskinesia scores, vital signs, and analog scale scores for mood, anxiety, and fatigue between 9 AM and 8 PM were examined. Adverse events on the double-blinded days were compared.

Results  Methylphenidate tended to increase the time "on" as measured by tapping (P = .09) but not by walking time or dyskinesia scores (P = .40 and .42, respectively). Methylphenidate tended to increase average tapping speed, decrease time to perform walking task, decrease tremor, and increase dyskinesia score but only the decrease in tremor reached significance. Neither the investigators nor the subjects could reliably identify active drug. Methylphenidate was well tolerated.

Conclusions  The effects of 0.4 mg/kg of MPD 3 times per day on the motor response to levodopa were small and variable and judged to be clinically insignificant.

Trial Registration  clinicaltrials.gov Identifier: NCT00359723

Author Affiliations: Department of Neurology (Dr Nutt and Ms Carter), and Public Health and Preventative Medicine, Division of Biostatistics (Dr Carlson), Oregon Health and Science University, Portland.

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