Abstract: The invention generally relates to compositions and methods with tramadol and an opioid antagonist to enhance analgesic potency and/or attenuate one or more adverse effects of tramadol, including adverse side effect(s) in humans such as nausea, vomiting, dizziness, headache, sedation (somnolence) or pruritis. This invention relates to compositions and methods for selectively enhancing the analgesic potency of tramadol and simultaneously attenuating anti-analgesia, hyperalgesia, hyperexcitability, physical dependence and/or tolerance effects associated with the administration of tramadol. The methods of the present invention comprise administering to a subject an analgesic or subanalgesic amount of tramadol and an amount of excitatory opioid receptor antagonist such as naltrexone or nalmefene effective to enhance the analgesic potency of tramadol and attenuate the anti-analgesia, hyperalgesia, hyperexcitability, physical dependence and/or tolerance effects of tramadol.

Abstract: This invention relates to a method for selectively enhancing the analgesic potency of a bimodally-acting opioid agonist such as morphine and simultaneously attenuating anti-analgesia, hyperalgesia, hyperexcitability, physical dependence and/or tolerance effects associated with the administration of the bimodally-acting opioid agonist. The method of the present invention comprises administering to a subject an analgesic or sub-analgesic amount of a bimodally-acting opioid agonist such as morphine and an amount of an excitatory opioid receptor antagonist such as naltrexone or nalmefene effective to enhance the analgesic potency of the bimodally-acting opioid agonist and attenuate the anti-analgesia, hyperalgesia, hyperexcitability, physical dependence and/or tolerance effects of the bimodally-acting opioid agonist.

Abstract: This invention relates to a method for treating a subject with irritable bowel syndrome (“IBS”) which comprises long-term administration of an opioid receptor antagonist at an appropriately low dose which will selectively antagonize excitatory opioid receptor functions, but not inhibitory opioid receptor functions, in myenteric neurons in the intestinal tract as well as in neurons of the central nervous system (“CNS”). The administration of the opioid receptor antagonist at a low dose enhances the potency of the inhibitory effects of endogenous opioid peptides present in the intestinal tract and the CNS, thereby reducing abdominal pain and stool frequency resulting from abnormally supersensitized excitatory opioid receptor functions. The invention also relates to a composition for treating a subject with IBS, which comprises an effective dose of an opioid receptor antagonist, and a pharmaceutically acceptable carrier.