The Effects of Aromatic Amino Acid Decarboxylase Inhibitors on Plasma Concentrations of 5‐Hydroxytryptophan in Man

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Abstract
5-Hydroxytryptophan is beneficial when administered alone or in combination with extracerebral aromatic amino acid decarboxylase inhibitors for therapeutic purposes in various disorders in which myoclonus is prominent. In 5 subjects the effect of decarboxylase inhibitors on the accumulation and elimination of 5-hydroxytryptophan in plasma was studied. The plasma concentrations of 5-hydroxytryptophan were increased about 10-fold by pretreatment with the decarboxylase inhibitors, carbidopa and benserazide. Half-lives of 2.2-3.0 h were obtained following oral administration of a single dose of 5-hydroxytryptophan with or without pretreatment. In 1 subject the half-life of 5-hydroxytryptophan in plasma increased to 5.5 h during long-term treatment with carbidopa.