3‐O‐methyldopa administration does not alter fluorodopa transport into the brain

To determine if 3‐O‐methyldopa (3OMd) significantly inhibits the transport of 6‐{¹⁸F} fluorodopa (6‐FD) into the brain at the concentration normally encountered during L‐dopa administration, we performed 6‐FD studies with positron emission tomography in cynomolgus monkeys in the presence and absence of 3OMd. Infusion of 3OMd was designed to produce plasma concentrations equivalent to those seen in patients on chronic L‐dopa therapy. Plasma 3OMd levels of 39 ± μM did not alter the blood–brain transfer rate of 6‐FD. 6‐FD positron emission tomographic studies in parkinsonian patients will therefore not be altered by 3OMd present in the blood in those patients taking L‐dopa preparations. These results do not support the hypothesis that transport of L‐dopa into the brain is inhibited by 3OMd to cause the declining response seen in patients with advanced Parkinson's disease.