Since motor fluctuations in Parkinsonian patients might be, at least in part, explained by an antagonism between levodopa (LD) and its metabolite 3-O-methyldopa (3-OMD) at bloodbrain-barrier (BBB), we decided to study LD and 3-OMD plasma and cerebrospinal fluid (CSF) levels in subjects undergoing lumbar puncture for diagnostic purposes. After informed consent, 70 subjects took a tablet of carbidopa-levodopa association (Sinemet or Sinemet-CR) 0.5, 1, 2, 4, 8, 12 h before blood and lumbar cerebrospinal fluid collection. LD and 3-OMD were determined by an HPLC-electrochemical method. The subjects treated with Sinemet-CR had lower LD cerebrospinal fluid concentrations along with lower LD and higher 3-OMD plasma concentrations. This pattern of LD cerebrospinal fluid concentrations may be explained by means of a transport competition between LD and 3-OMD at blood brain barrier level.
