Postoperative analgesia by intraarticular clonidine and neostigmine in patients undergoing knee arthroscopy

Background and Objective: Clonidine and neostigmine have a central mechanis m of analgesic action and are synergistic when given intrathecally. Both dr ugs also have a peripheral analgesic effect. The purpose of this study was to compare the analgesic effect of intraarticular clonidine and neostigmine , used separately and in combination, in patients undergoing knee arthrosco py. Methods: Eighty-four American Society of Anesthesiologists (ASA) I and II p atients scheduled for meniscus repair under arthroscopy were allocated rand omly in 6 groups to receive in a double-blind manner at the end of surgery 150 mug of intraarticular clonidine with subcutaneous saline, 500 mug of in traarticular neostigmine with subcutaneous saline, an intraarticular combin ation of 150 mug of clonidine and 500 mug of neostigmine with subcutaneous saline, 150 mug of intraarticular clonidine with 500 mug of subcutaneous ne ostigmine, 500 Ag of intraarticular neostigmine with 150 mug of subcutaneou s clonidine, or intraarticular and subcutaneous isotonic saline. Postoperat ive pain scores were measured on a visual analog scale (VAS) at rest and on mobilization. Paracetamol (I g) was given as a rescue medication when pain score was greater than 40. Results: VAS scores at rest and on mobilization were lower in the first 5 g roups compared with the intraarticular saline group (P < .05), but no signi ficant difference was documented between the treated groups. The time to th e first paracetamol administration was shorter in the saline group compared with the other groups, and the paracetamol demand was also higher in this group. Forty-five percent of the patients who had received clonidine had at least I episode of hypotension versus 4% of those who did not (P < .01). T he incidence of bradycardia was 20% and 0%, respectively (P = .01). The inc idence of nausea was not statistically different in patients who did and di d not receive neostigmine (43% v 36%, respectively). Conclusion: Intraarticular administration of 150 mug of clonidine, 500 Ag o f neostigmine, or both produce postoperative analgesia, and the combination is not more effective.