Predicted fold increase in the AUCs of codeine and morphine based on plasma ketamine concentrations reported following anesthetic and analgesic doses

ReferenceKTM DoseTotal Plasma [KTM] (μM)aPredicted Fold Increases in Codeine and Morphine AUC Ratios Based on Reported Total and Unbound In Vivo Ketamine Concentrations
Codeine ([KTM]total)Codeine ([KTM]unbound)Morphineb ([KTM]total)Morphineb ([KTM]unbound)
Idvall et al. (1979)2 mg + 41 μg · min−1 · kg−1 i.v.9.32.392.121.611.50
Xie et al. (2003)0.5 mg/kg epidurally2.71.541.411.261.20
Clements and Nimmo (1981)0.125–0.25 mg/kg i.v.0.42c1.
  • a Unbound ketamine concentration calculated as fu × total plasma concentration.

  • b Morphine AUC ratios represent the sum of the separate ratios for the 3- and 6-glucuronidation pathways.

  • c Pain threshold increased >5 min when total plasma ketamine concentration was >100 μg/l.