Some clinicians think it is reasonable to continue selegiline once it has been started. If selegiline is later shown not to have a neuroprotective effect, little harm will have been done. If, on the other hand, the drug is later shown to have such an effect, patients who did not receive it may have needlessly suffered a greater loss of neurons than those who did. The choice of drugs used in the treatment of PD is determined in part by the relative chronologic and biologic age of the patient. If its effect wanes and other antiparkinsonian medications are added, amantadine should be discontinued to avoid unnecessary polypharmacy.
Gradual withdrawal is recommended to prevent acute exacerbation of parkinsonian symptoms.
This drug's major advantage is a low incidence of side effects but, since it is excreted largely unchanged in the urine, it should be used with caution in patients with renal failure. Peripheral vascular side effects include livedo reticularis and ankle edema, but these are rarely severe enough to limit treatment. Confusion, hallucinations, insomnia, and nightmares can occur but are less common in patients aged 60 years or less, and they are more likely to occur when amantadine is used in combination with other antiparkinsonian drugs. Dry mouth and blurred vision are presumed to be peripheral anticholinergic side effects, but they seem to occur more commonly when amantadine is given in combination with anticholinergic drugs. In summary, amantadine is indicated for early treatment of PD in patients 60 years of age or less who have mild akinesia and rigidity and in whom tremor is not a major problem.