title: Effect of nicotine on the pharmacokinetics of levodopa.
abstract: OBJECTIVE
  Some patients with Parkinson disease improved their symptoms on treatment with nicotine patch or gum. Nicotine has also been studied for its antidyskinetic effect on levodopa-induced dyskinesia. We determined the effects of nicotine on levodopa pharmacokinetics and gastric emptying in healthy subjects and on levodopa transport in Caco-2 monolayers in vitro.
  
  
  METHODS
  Healthy subjects received transdermal nicotine patch application followed by oral levodopa/benserazide, 100/25 mg, in a fasting state and with enteral nutrition. Levodopa pharmacokinetics was determined, and gastric emptying was evaluated by carbon 13 ((13)C)-labeled acetic acid breath testing. In vitro studies using intestinal Caco-2 cell monolayers evaluated whether the intestinal transport of levodopa was affected by nicotine and its metabolite, cotinine.
  
  
  RESULTS
  Nicotine did not increase mean plasma concentration significantly during fasting or with enteral nutrition, although the extent of levodopa absorption was reduced by 34% to 60% in some individuals and the mean plasma concentration of levodopa was statistically decreased by nicotine in subjects who received enteral nutrition. However, gastric parameters were not significantly affected by nicotine. Nicotine and cotinine at 0.1 μmol/L significantly reduced levodopa uptake by Caco-2 cells (P < 0.01).
  
  
  CONCLUSIONS
  We found that nicotine reduced plasma levodopa concentration in some healthy subjects but with no alteration of gastric emptying rate. In vitro, nicotine inhibited levodopa transport by Caco-2 cell monolayers in an α-methyl amino isobutyric acid-independent, 2-amino-norbornanecarboxylic acid-dependent manner. These results suggest that nicotine may inhibit the transport of levodopa by the system L-amino acid transporter.
authors.affiliation: Department of Neurology and Therapeutic Medicine, Ehime University Hospital and Graduate School of Medicine, Shitsukawa, Tohon, Ehime, Japan.
authors.forename: Win Thiri
authors.initials: WT
authors.lastname: Kyaw
authors.forename: Masahiro
authors.initials: M
authors.lastname: Nagai
authors.forename: Mika
authors.initials: M
authors.lastname: Kaneta
authors.forename: Madoka
authors.initials: M
authors.lastname: Kubo
authors.forename: Noriko
authors.initials: N
authors.lastname: Nishikawa
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Tsujii
authors.forename: Hirotaka
authors.initials: H
authors.lastname: Iwaki
authors.forename: Masahiro
authors.initials: M
authors.lastname: Nomoto
mesh_terms: D000279:Administration, Cutaneous; D000284:Administration, Oral; D000328:Adult; D018938:Caco-2 Cells; D018592:Cross-Over Studies; D004347:Drug Interactions / Q000502:physiology; D020820:Dyskinesias / Q000188:drug therapy* / Q000209:etiology / Q000473:pathology; D005746:Gastric Emptying / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D007413:Intestinal Mucosa / Q000187:drug effects* / Q000473:pathology; D007980:Levodopa / Q000009:adverse effects / Q000493:pharmacokinetics*; D008297:Male; D008875:Middle Aged; D009538:Nicotine / Q000009:adverse effects / Q000494:pharmacology*; D061485:Tobacco Use Cessation Devices; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D007980:Levodopa; D009538:Nicotine