CSF AND BLOOD PHARMACOKINETICS OF HYDROMORPHONE AND MORPHINE FOLLOWING LUMBAR EPIDURAL ADMINISTRATION

Sixteen consenting patients scheduled for elective thoracotomy were enrolled into a randomized trial of epidural morphine and hydromorphone. Each patient had a lumbar epidural catheter placed preoperatively for the purpose of post-thoractomy analgesia. Shortly before the end of the operative procedure each patient received 5 mg of morphine and 0.75 mg of hydromorphone via the epidural catheter. Blood was sampled at regular intervals following the opiate administration and patients were randomized to 1 of 7 cervical CSF sampling times. Blood and CSF samples were assayed for morphine and hydromorphone concentration to determine blood and CSF pharmacokinetic profiles. A maximum blood morphine concentration of 60 +/- 25 ng/ml (mean +/- S.D.) was obtained at 11 +/- 6 min (mean +/- S.D.). The blood hydromorphone peak of 14 +/- 13 ng/ml (mean +/- S.D.) occurred 8 +/- 6 min (mean +/- S.D.). The mean peak CSF opioid concentrations of 1581 ng/ml for morphine and 309 ng/ml for hydromorphone occurred 60 min after epidural administration. The blood and CSF pharmacokinetic profiles for morphine and hydromorphone are presented. These profiles are similar for the two drugs after lumbar epidural administration.