Long-Term Effects of Amantadine in Parkinsonian (AMANDYSK)

This is a French national trial, conducted using a double-blind, placebo-controlled, randomised design involving 7 centers and 80 patients of both sexes. The primary objective of the trial is to evaluate the effects of the interruption of a long term treatment (ex. Greater than 6 months) with Amantadine (prescribed as an antidyskinetic) in patients suffering from Parkinson disease being treated with Levodopa and suffering from mid dose dyskinesias. Secondary objectives of the trial are the evaluation of the other effects of withdrawal of Amantadine on the same group of patients: motor fluctuations, vigilance, apathy, fatigue, certain cognitive aspects, the disappearance or development of undesirable side effects and quality of life.

The trial will involve the participation of the patients for a period of 3 months each. The two groups of patients to be studied are: * a group who will continue their treatment with Amantadine with no modification to dosage; * a group who will have their dosage of Amantadine progressively replaced over several days with a placebo (with the aim of avoiding a "brutal" withdrawal which has been associated with symptoms of hyperthermia in rare cases in the literature). The trial visits are scheduled as such: * weekly visits for the first 4 weeks, with a telephone call between each visit to assure that the withdrawal from Amantadine causes any problems. * every 2 weeks from week 4 until week 8, with weekly telephone calls in between these visits. * a telephone call in the 10th week followed by an end of study visit in week 12. In the event of an early withdrawal from the trial, and assuming that the patient gives their consent, a complete end of study visit will be performed prior to recommencing open label treatment with Amantadine in progressively increasing doses (100mg every 3 days until the pre-study dose is reached).