“On‐off” phenomenon with levodopa therapy in parkinsonism
Clinical and pharmacologic correlations and the effect of intramuscular pyridoxine
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Abstract
Five parkinsonian patients with severe “on-off” effects from levodopa therapy also were given combination carbidopa/levodopa. Serial half-hourly measurements of plasma levels of dopa, 3-O-methyldopa, and homovanillic acid showed partial concordance between clinical fluctuation and plasma dopa levels in patients receiving levodopa alone or in combination with carbidopa. The combination therapy does not lessen “on-off” effects except when administered in greater and more-frequent doses, which are permitted by the improved gastrointestinal tolerance with carbidopa/levodopa. A single intramuscular injection of pyridoxine has no clinical effect and slightly lowers subsequent plasma dopa only in the absence of carbidopa. Possible biochemical mechanisms are discussed.
- © 1974 by the American Academy of Neurology
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