Levadopa

• Levadopa (precursor of dopamine)  restores dopamine levels by being converted by enzymes to dopamine
• drug of choice (75% get 50% reduction in symptoms) – full response takes 2-3 months, but after 5 years less effective
• crosses blood-brain by active transport, then taken up into remaining dopaminergic nerve terminal in the striatum  converted to dopamine
• administered orally; absorbed rapidly by GI tract; only small amount reaches brain (metabolised by decarboxylase enzymes)
• effectiveness reduced when used with vitamin B6, phenytoin or benzodiazepines; MAO inhibitors increase risk for hypertension.
• contraindications – narrow angle glaucoma;
• adverse effects – nausea and vomiting (especially early), orthostatic hypertension, involuntary movements of limbs and face (dyskinesia), hallucinations and other psychiatric effects (common reason for limiting use).

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