PLASMA-CONCENTRATIONS AND DISPOSITION OF CLONIDINE FOLLOWING A CONSTANT 14-DAY EPIDURAL INFUSION IN CANCER-PATIENTS

Epidural administration of clonidine, a partial alpha(2)-adrenergic ag onist, provides effective relief for patients with intractable cancer pain. However, clonidine's long plasma elimination half-life suggests a potential for plasma accumulation following repeated doses or consta nt infusion. Adult male and female cancer patients experiencing severe , intractable pain were administered a continuous epidural infusion (3 0 mu g/h) of clonidine hydrochloride for 14 days. Plasma clonidine con centrations were determined for 31 patients using a radioimmunoassay w ith a limit of quantitation of 0.062 ng/mL. Mean (+/- SD) plasma cloni dine concentration and calculated total body clearance after 7 days of infusion (respectively, 2.19 +/- 1.17 ng/mL, n = 24; 279 +/- 184 mL/m in, n = 27) were comparable to those following 14 days of infusion (2. 50 +/- 1.51 ng/mL, n = 19; 272 +/- 163 mL/min, n = 21). Clonidine does not appear to accumulate in the plasma compartment during prolonged ( 14-day) continuous epidural infusion in cancer patients.