To the Editor.—
Recent reports in The Journal have clearly indicated the negative effects of pyridoxine on the therapeutic response of patients with parkinsonism to levodopa.1,2 Blood dopa levels have been demonstrated as decreased and clinical disability augmented following co-administration of dopa and pyridoxine. It is believed that these responses are due to an activation of systemic dopa decarboxylation by the vitamin. Cotzias et al3 have theorized and presented supportive clinical data that, under conditions of peripheral decarboxylase inhibition, as produced by the inhibitor α-methyldopa hydrazine (MK-486), the antagonistic actions of pyridoxine to dopa effect are reversed. Enhancement may result, as evidenced by lower daily dopa requirements and sudden onset of toxic effects.In order to investigate this effect further, mice were injected intraperitoneally with placebo, levodopa (100 mg/kg), MK-486, (50 mg/kg), and pyridoxal-5-phosphate, (5 mg/kg), singly or in combination. One hour later, the animals were killed, and
Mars H, Barrera ER, Bennett S. Levodopa and Pyridoxine. JAMA. 1972;219(13):1764. doi:10.1001/jama.1972.03190390048026
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