VARIATIONS IN L‐DOPA ABSORPTION

Abstract. In a parkinsonian patient with a weak effect of L‐dopa on the parkinsonian symptoms, unusually high plasma levels of dopa and dopamine sulphate were noticed. The plasma concentrations of tyrosine and phenylalanine were low during the whole observation period. The urinary excretion of dopamine sulphate and the ratio of dopamine sulphate to dopamine in urine were high. The reason for this high ratio of dopamine sulphate to dopamine could not be determined. The disappearance of L‐dopa from plasma after i.v. administration was only slightly reduced. It was concluded that the L‐dopa absorption in this patient was very efficient due to a low dopa decarboxylation in the intestinal organs in spite of a normal decarboxylase activity in other peripheral tissues. Such a selective decrease in the dopa decarboxylation in the intestinal. organs is presumably unusual, but illustrates that very marked individual variations in the L‐dopa metabolism may occur in parkinsonian patients.