The disposition of the tolcapone 3-O-methylated metabolite is affected by the route of administration in rats

J Pharm Pharmacol. 1994 Jul;46(7):571-4. doi: 10.1111/j.2042-7158.1994.tb03859.x.


Catechol-O-methyltransferase (COMT) catalyses the transfer of the methyl group from S-adenyl-L-methionine (SAM) to one of the hydroxy groups of a catechol, usually the hydroxy group in position 3. COMT is present mainly in a soluble form (S-COMT) in the cytosol, but a small fraction is bound to cell membranes (MB-COMT). MB-COMT has higher affinity for the catechol substrate than does S-COMT by a factor of > 10, and high MB-COMT activity is observed in the intestinal muscle layer. The present study investigates the effect of the administration route on the disposition of the tolcapone 3-O-methylated metabolite following intravenous and oral tolcapone administration in rats. Tolcapone is a substrate for COMT although the 3-O-methylated metabolite produced has no pharmacological actions. The 3-O-methylated metabolite was eliminated very slowly following oral administration of tolcapone, and its concentration approached a plateau level, which was in contrast to the situation following intravenous administration of tolcapone. It is thought that the oral dose of tolcapone receives a high exposure to MB-COMT in the intestinal muscle layer during its absorption, and tolcapone seems to form a complex with MB-COMT having a high affinity constant (i.e. a very low Ki). The fraction of the intravenous dose of tolcapone metabolized to the 3-O-methylated metabolite at 10 mg kg-1 was 2.6%, whereas those of the oral doses, which were corrected by the bioavailability, were 5.4% for 20 mg kg-1 and 2.7% for 40 mg kg-1.

Publication types

  • Comparative Study

MeSH terms

  • Administration, Oral
  • Animals
  • Antiparkinson Agents / administration & dosage
  • Antiparkinson Agents / metabolism
  • Antiparkinson Agents / pharmacokinetics*
  • Benzophenones / administration & dosage
  • Benzophenones / pharmacokinetics*
  • Biological Availability
  • Catechol O-Methyltransferase Inhibitors*
  • Chromatography, High Pressure Liquid
  • Dose-Response Relationship, Drug
  • Injections, Intravenous
  • Intestinal Absorption / drug effects
  • Intestinal Mucosa / metabolism*
  • Male
  • Methylation
  • Muscle, Smooth / metabolism
  • Nitrophenols
  • Rats
  • Rats, Sprague-Dawley
  • Regression Analysis
  • Substrate Specificity
  • Tolcapone


  • Antiparkinson Agents
  • Benzophenones
  • Catechol O-Methyltransferase Inhibitors
  • Nitrophenols
  • Tolcapone