Pyridoxine Antagonism of Levodopa in Parkinsonism

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Abstract
Since the decarboxylation of dopa to form dopamine is dependent upon pyridoxal phosphate, Duvoison and co-workers1 hypothesized that pyridoxine might enhance the therapeutic effects of levodopa. Accordingly, they administered pyridoxine hydrochloride to patients with parkinsonism who were receiving maintenance doses of levodopa. They found that large doses of pyridoxine completely eliminated the clinical effects of levodopa, while smaller doses reduced or abolished its therapeutic activity or only dyskinetic side effects. This was associated with a reduced rise in plasma dopa levels following levodopa administration. Other workers have also reported reduced clinical activity of levodopa following pyridoxine.2-3 The purpose of the present study was to correlate the effects of pyridoxine on the therapeutic activity of levodopa with its effects on absorption and metabolism. Materials and Methods The study population consisted of three men and one woman with parkinsonism who had achieved stable improvement (Table 1). Maintenance levels of levodopa

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