Mr 2033 CL--a novel non-morphine-like opioid analgesic

Mr 2033 CL is a very potent non-morphine-like opioid analgesic as shown in different test models and animal species. On a weight for weight basis, it is about 20 times more potent than morphine. The analgesic effects of Mr 2033 CL are supposed to be different from those of morphine and bremazocine because of individual sensitivity against selective antagonists like naloxone and Mr 2266 CL. Mr 2033 CL does not induce the Straub tail phenomenon and increased circling movements in mice, catatonia in rats, and stupor in rabbits which are characteristic for mu agonists. Moreover, Mr 2033 CL does not have a morphine-like abuse potential in rats, dogs and rhesus monkeys. CNS-depressive effects were observed in different species. Respiratory depression and inhibition of intestinal transit seem to be of minor degree. In contrast to morphine, Mr 2033 CL provokes diuresis in rats. Binding studies in rats as well as dependence studies in rats and rhesus monkeys characterize Mr 2033 CL as a predominant kappa agonist with morphine antagonistic properties.