Name: L-Dopa
Class: Antiparkinsonian Agent (Precursor)
Mechanism: Inactive. Converted to dopamine in the brain by L-aromatic acid decarboxylase.
Absorption: Oral. Absorbed from small intest. via non-specific AA transport system. Absorption slowed if other AAs present (i.e., if taken w/food).
Dist.:
Metabolism.: MAO-B, COMT Excretion, t½:
T/S.E.s: Wearing off—decreased length of effect. Each dose effective for only 1-2 hr., followed by rapid return of motor deficits. Possibly controllable w/ dose & frequency of dosing. Dyskinesias—excessive & abnormal involuntary movements (dystonia, esp. upon waking w/low plasma levels; choreiform dyskinesia occurs during peak levels). On/off phenom.—In late PD, patient rapidly fluctuates btwn. having no beneficial effect from L-Dopa to having good mobility (but often w/signif. dyskinesia). Others—hallucinations & confusion (clozapine may help), cardiac arrhythmias (rare), life-threatening hypertension & pyrexia if coadmin. w/non-specific MAO inhibitor, may exacerbate/ppt. melanoma in predisposed patients. C/I w/closed-angle glaucoma. Vit. B6 may ¯ efficacy.
Utility: Treat Parkinson’s Disease symptoms. May initially produce complete improvement in rigidity, bradykinesia, & tremor.
Features: Must be admin. w/a peripheral decarboxylase inhibitor—carbidopa (carbidopa/L-Dopa = Sinemet), benserazide.