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February 28, 1972

Low Pyridoxine Diet In Parkinsonism

Author Affiliations

New Haven, Conn

JAMA. 1972;219(9):1211. doi:10.1001/jama.1972.03190350047018

To the Editor.—  Recently low pyridoxine (vitamin B6) diets have been distributed by some pharmaceutical companies to be used in conjunction with levodopa in the treatment of parkinsonism. Presumably, this dietary recommendation was prompted by the observation that administered pyridoxine neutralizes the therapeutic action of levodopa in patients with parkinsonism.1 Levodopa is decarboxylated to dopamine by a pyridoxal 5′ phosphate-dependent enzyme. Administration of pyridoxine increases peripheral metabolism of levodopa, thereby reducing the amount of levodopa available for transport into the brain. Although a low pyridoxine diet might be expected to increase the proportion of levodopa reaching the brain, other factors suggest that the use of this diet could be an unwise or even dangerous procedure. After absorption, pyridoxine is converted enzymatically into pyridoxal 5′ phosphate.2 Pyridoxal 5′ phosphate nonenzymatically reacts at physiological pH with dopamine and levodopa as well as other amino acids to form Schiff bases,