Methylnaltrexone prevents morphine-induced delay in oral-cecal transit time without affecting analgesia: a double-blind randomized placebo-controlled trial.
Methylnaltrexone is a quaternary opioid antagonist with limited ability to cross the blood-brain barrier and the potential to antagonize the peripherally mediated effects of opioids. The effectiveness of methylnaltrexone in preventing morphine-induced changes in gastrointestinal motility and transit without affecting analgesia was evaluated in humans. Twelve healthy volunteers were given intravenous placebo, placebo plus 0.05 mg/kg morphine, or 0.45 mg/kg methylnaltrexone plus 0.05 mg/kg morphine. Oral-cecal transit time was assessed by the pulmonary hydrogen measurement technique, and analgesia was measured with use of the cold-pressor test. Morphine significantly increased oral-cecal transit time from 104.6 +/- 31.1 minutes (mean +/- SD) to 163.3 +/- 39.8 minutes (p