Clements J A, Nimmo W S, Grant I S
J Pharm Sci. 1982 May;71(5):539-42. doi: 10.1002/jps.2600710516.
The pharmacokinetics of ketamine in analgesic doses after intravenous, intramuscular, and oral administration was investigated in healthy volunteers. Plasma ketamine concentration-time curves were fitted by a two-compartment open model with a terminal half-life of 186 min. Absorption after intramuscular injection was rapid and the bioavailability was 93%. However, only 17% of an oral dose was absorbed because of extensive first-pass metabolism. Simultaneous measurements of the elevation of pain threshold in an ischemic exercise test showed a marked effect for 15-60 min after intramuscular injection, but little or no effect after the oral solution. Pain threshold elevation occurred at plasma ketamine concentrations above 160 ng/ml.
