title: L-dopa decarboxylation in chronically treated patients.
abstract: We measured decarboxylation of oral L-dopa in patients chronically treated with L-dopa, and in untreated controls. Chronic L-dopa and carbidopa administration did not affect the extent of whole-body decarboxylation, and it is therefore unlikely that on-off fluctuations are related to chronic changes in the activity of L-aromatic amino acid decarboxylase. The observed duration of action and dose-response properties of carbidopa suggested that current empirically based dose schedules are optimal and supported the concept that decarboxylase inhibitors enhance the clinical effect of L-dopa largely by reducing the extent of first-pass metabolism rather than through an action on the decarboxylase enzyme in cerebral capillaries.
mesh_terms: D000328:Adult; D002230:Carbidopa / Q000627:therapeutic use; D002625:Chemistry, Organic; D003653:Decarboxylation; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D007980:Levodopa / Q000378:metabolism* / Q000627:therapeutic use; D008297:Male; D055601:Organic Chemistry Phenomena; D010300:Parkinson Disease / Q000188:drug therapy / Q000378:metabolism*; D013997:Time Factors
chemical_list: D007980:Levodopa; D002230:Carbidopa