Subchronic administration of (R,S)-ketamine induces ketamine ring hydroxylation in Wistar rats

J Pharm Biomed Anal. 2016 Aug 5;127:3-8. doi: 10.1016/j.jpba.2016.03.030. Epub 2016 Mar 14.


Subchronic administration of (R,S)-ketamine, (R,S)-Ket, is used in the treatment of neuropathic pain, in particular Complex Regional Pain Syndrome, but the effect of this protocol on the metabolism of (R,S)-Ket is unknown. In this study, daily administration of a low dose of (R,S)-Ket for 14-days to Wistar rats was conducted to determine the impact of sub-chronic dosing on the pharmacokinetics of (R,S)-Ket and its major metabolites. The data indicate that, relative to a single administration of (R,S)-Ket, subchronic administration resulted in increased clearance of (R,S)-Ket and the N-demethylated metabolite norketamine measured as elimination half-life (t1/2) and decreased plasma concentrations of these compounds. Subchronic administration produced a slight decrease in t1/2 and an increase in plasma concentration of the major metabolite, (2S,6S;2R,6R)-hydroxynorketamine, and produced significant increases in the plasma concentrations of the (2S,6R;2R,6S)-hydroxynorketamine and (2S,4R;2R,4S)-hydroxynorketamine metabolites. The metabolism of (R,S)-Ket predominately occurs via two microsomal enzyme-mediated pathways: (R,S)-Ket⇒(R,S)-norketamine⇒(2S,6S;2R,6R)-hydroxynorketamine and (2S,4R;2R,4S)-hydroxynorketamine and the (R,S)-Ket⇒(2S,6R;2R,6S)-hydroxyketamine⇒(2S,6R;2R,6S)-hydroxynorketamine and (2S,6S;2R,6R)-hydroxynorketamine. The results indicate that the activity of both metabolic pathways are increased by subchronic administration of (R,S)-Ket producing new metabolite patterns and potential differences in clinical effects.

Keywords: (2S,6R)-hydroxynorketamine; Complex Regional Pain Syndrome; Neuropathic pain.

MeSH terms

  • Analgesics / administration & dosage*
  • Analgesics / blood
  • Analgesics / chemistry
  • Analgesics / pharmacokinetics*
  • Animals
  • Area Under Curve
  • Biotransformation
  • Dose-Response Relationship, Drug
  • Half-Life
  • Hydroxylation
  • Injections, Intraperitoneal
  • Ketamine / administration & dosage*
  • Ketamine / blood
  • Ketamine / chemistry
  • Ketamine / pharmacokinetics*
  • Male
  • Metabolic Networks and Pathways / drug effects
  • Rats, Wistar
  • Stereoisomerism


  • Analgesics
  • Ketamine