Pharmacokinetics of rectal ketamine in children

We have studied the pharmacokinetics of ketamine administered rectally in a dose of 10 mg kg-1 to five children aged 6-9 yr and mean weight 28.80 (SD 6.55) kg. An acceptable level of anaesthesia was not obtained in any patient. Despite this, the degree of analgesia obtained was good and no child required further administration of analgesics during the postoperative period. Tolerance to the suppositories was excellent. The absorption of ketamine was found to be relatively fast, with a median peak concentration of 160 ng ml-1 (range 96-250 ng ml-1) at 0.75 h (range 0.50-1.00 h) after administration. The plasma concentrations of norketamine were greater than those of the parent drug, with a maximum of 510 ng ml-1 (range 450-810 ng ml-1) at 0.81 h (range 0.50-1.00 h) after administration. The medians of the half-lives of ketamine and norketamine were 3.15 h and 2.56 h, respectively (range 1.57-4.95 h and 1.47-5.30 h, respectively).