ENHANCED POTENCY OF INTRAVENOUS, BUT NOT INTRATHECAL, MORPHINE AND MORPHINE-6-GLUCURONIDE AFTER BURN TRAUMA

We examined the analgesic effect of morphine (M) and its metabolite mo rphine-6-glucuronide (M6G) in a rat model of acute thermal trauma. M o r M6G were given by intrathecal (IT) or intravenous (IV) routes after brief burn or sham burn delivered during inhalational anesthesia. In t he sham group, M6G was significantly less potent than M when given IV, yet tended to be more potent than M when given IT. For both drugs, th ermal injury increased IV potency, yet decreased (for M) or displayed a trend to decrease (for M6G) IT potency. The increased potency seen w ith IV but not IT opioid administration may reflect pharmacokinetic (e .g., diminished clearance) and/or pharmacodynamic responses (e.g., act ivation of peripheral opioid receptors) after thermal injury.