[The pharmacokinetics of continuous peridural morphine infusion]

In patients with cancer pain treated by continuous epidural opiate infusion (4.5-24 mg morphine per day) via implanted or portable pumps (n = 40) plasma levels of morphine were determined during the postoperative period and during regular refill of the pump systems. Concentrations were between 2.6 and 18.8 ng/ml depending on daily dosage and body weight. There were no signs of accumulation. Concentrations in lumbar CSF measured in some of the patients were 15-20 higher but decreased by 10-20% (in relation to daily dosage) in the course of long-term treatment. This may be induced by reduction in permeability of the dura due to fibrosis within the epidural space after chronicle catheterization. Cervical CSF concentrations (during chordotomy) were about 1/6 to 1/7 of the corresponding lumbar CSF levels. It may be assumed that epidural opiate infusion in spite of low blood levels is accompanied by relevant cerebral opiate actions.