To the Editor.—
On theoretical grounds, extra attention should be paid to patients with Parkinson's disease being considered for levodopa therapy who also have conditions rendering them relatively pyridoxine deficient. Among the conditions associated with relative pyridoxine deficiencies are certain illnesses (diabetes mellitus, chronic alcoholism, malnutrition, and malignancies), industrial exposures (hydrazine-containing rocket fuels1 ), and drug therapies (isoniazid2 or cycloserine3 for tuberculosis and penicillamine4 for Wilson's disease, cystinuria, and heavy metal intoxication). In patients with these conditions, supplemental pyridoxine hydrochloride is often used.
Several investigators have now reported that pyridoxine antagonizes the beneficial effects of levodopa,5-8 and at least one multiple vitamin preparation without pyridoxine is now available because of this.
The Food and Drug Administration, in releasing levodopa, has required the manufacturers to continue reporting upon its clinical efficacy and hazards. Because I am not aware of any completed documentation of the interaction of levodopa with
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