Spinal clonidine produces less urinary retention than spinal morphine

We have conducted a double-blind, randomized study in two groups of 20 patients each, undergoing hip surgery during spinal anaesthesia, to compare the incidence of urinary retention after spinal morphine or clonidine. Patients received 0.5% spinal bupivacaine 15 mg combined with either clonidine 75 mu g or morphine 0.2 mg. After operation, patients were examined for micturition, bladder distension, or both, when they failed to void, they received naloxone 0.2 mg, and if bladder distension persisted, a catheter was inserted. At 12 h, all patients in the morphine group but only five in the clonidine group had bladder distension, and at 24 h this was present in seven and one patient in the morphine and clonidine groups, respectively (P < 0.001). Naloxone was given in 16 and one, and a catheter was placed in one and six patients in the morphine and clonidine groups, respectively (P < 0.001). We conclude that spinal clonidine impaired bladder function to a lesser extent than morphine.