Postoperative analgesia using a low-dose, oral-transdermal clonidine combination: lack of clinical efficacy

To determine if a lower than previously reported oral-transdermal clonidine regimen could reduce postoperative morphine requirements without producing systemic side effects.

Double-blind, randomized, placebo-controlled study.

University-affiliated hospital.

29 healthy, ASA physical status I and II females undergoing elective abdominal hysterectomy.

Patients received preoperative oral clonidine 4 to 5 mu/kg and a 7 cm2 transdermal clonidine patch (0.2 mg/24 hours) or a placebo tablet and patch.

Postoperative patient-controlled analgesia pumps provided morphine during the 48-hour study period. Morphine use, hemodynamic changes, and nonhemodynamic side effects were recorded. Additionally, visual analog pain scales (VAPS) and plasma concentrations of morphine and clonidine were measured. We found that low-dose clonidine had no potentiating effect on morphine analgesia. Postoperative morphine use, VAPS, and morphine plasma levels were similar between the control and clonidine-treated groups. Nevertheless, patients in the clonidine group experienced a significantly greater incidence of intraoperative and postoperative hypotension and bradycardia than did the control group. No differences were noted in the incidence of nonhemodynamic side effects.

The low-dose oral-transdermal clonidine regimen evaluated failed to reduce postoperative morphine requirements, although patients who received clonidine were still at risk for developing hypotension.