Effects of Opioids on the Absorption of Alcohol

Administration of opiate agonists and antagonists has been shown to increase and decrease alcohol consumption, respectively. Because opioids can affect gastric emptying and decrease intestinal motility, the present experiments were done to determine whether changes in alcohol consumption following opioid administration might be due to opioid-induced changes in the pharmacokinetics of alcohol. In experiment 1, morphine in doses ranging from 1.5 to 4.5 mg/kg dose dependently decreased the absorption of alcohol induced by oral intubation (1 g/kg) and reduced peak blood alcohol levels (BALs). Naltrexone in doses ranging from 1.5 to 4.5 mg/kg produced a small, but significant, reduction in the absorption of alcohol, but the effects were not dose related. Similar effects of morphine and naltrexone on alcohol absorption were observed in rats infused with alcohol (1 g/kg) through an implanted intragastric cannula. The effects of morphine on alcohol absorption were observed whether alcohol levels were determined from tail vein or arterial blood samples or from brain samples. The effects of morphine on alcohol absorption were not blocked by pretreatment with methyl-naltrexone. However, the peripherally acting opioid agonist loperamide reduced BALs in a manner similar to morphine. These studies indicate that although opiate agonists and antagonists modify alcohol absorption to different extents, their effects on BALs are not a sufficient condition to induce changes in alcohol consumption.