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Metabolic Interactions

Harold Mars, MD, CM, FRCP(C)

Arch Neurol. 1974;30(6):444-447.

Abstract
Exogenous pyridoxine is known to antagonize the neuropharmacologic action of levodopa in Parkinson disease. The metabolic interactions of levodopa, pyridoxine, and carbidopa, a peripheral decarboxylase inhibitor, were studied in 15 long-term, levodopa-treated patients. Pyridoxine reduced plasma dopa levels 67% but enhanced homovanillic acid synthesis 49% Carbidopa potentiated plasma dopa, inhibited homovanillic acid synthesis, and minimized the effects of pyridoxine.

The decarboxylase activity index following pyridoxine administration increased 483% and 136% for plasma and urine respectively. Carbidopa effected a 77% and 94% reduction.

It is suggested that pyridoxine accelerates systemic metabolism of levodopa, thereby decreasing availability of the amino acid to brain parenchyma. The combination of levodopa and carbidopa prevents the loss of levodopa effect produced by exogenous pyridoxine.

Author Affiliations
Cleveland

From the Division of Medicine, Department of Neurology, Mt. Sinai Hospital, Case Western Reserve University, Cleveland.

Footnotes
Accepted for publication Oct 29, 1973.

Read in part before the combined 98th annual meeting of the American Neurological Association and the 25th annual meeting of the Canadian Neurological Society, Montreal, June 13, 1973.

Reprint requests to Division of Medicine, Department of Neurology, Mt. Sinai Hospital, Case Western Reserve University, Cleveland, OH 44106 (Dr. Mars).

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