78.4 minutes and volume of distribution of 0.58 +/- 0.20 L/kg. Peak plasma levels are reached within 0.5-4.0 h after dosing, decline of plasma concentrations after the peak follow a biphasic pattern, with half-lives of 0.4-1.6 h for the first phase and 6.3-21.8 h for the terminal phase. While in about 40% of patients, half-lives from 1.5 to 4.7 h, in a monophasic manner. Less than 0.06% of the dose is excreted unchanged in urine within 8 h of administration. Chemistry Dextromoramide is the right-handed isomer of the moramide molecule. The left-handed molecule is called levomoramide, and a mixture of the two is called racemoramide. Its full chemical name is (+)-1-(3-Methyl-4-morpholino-2,2-diphenylbutyryl)pyrrolidine, and its molecular formula: C25H32N2O2, with an atomic weight of ~392.5. Dextromoramide was discovered during the course of research into a related family of compounds, the α,α-Diphenyl-γ-Dialkyamino-Butyramides, which show no analgesic activity, but are extremely active physiologically as inhibitors of gastric secretions in man. Other drugs from this series show antispasmodic and antihistamine effects, but most research was put into researching analgesics. The structure-activity relationships of this family of drugs was investigated extensively, with dextromoramide representing the optimisation of several different structural features; (i) at the 1-amide group only the pyrrolidine and dimethylamide substituents were active, with pyrrolidine being more potent (ii) the alkyl chain was more potent when methylated, 3-methylation was more potent than 4-methylation, and in the 3-methyl analogues the dextro isomer was more active (iii) while morpholine, dimethylamine, pyrrolidine and piperidine were all active at the 4-amine group, morpholine was the most active (iv) any substitution on the phenyl rings reduces activity. So dextromoramide, with a pyrrolidine ring on the 1-amide position, a dextro methyl group on the 3-position of the alkyl chain, a morpholine ring around the 4-amine group, and both phenyl rings unsubstituted, was by far the most potent out of all the compounds in this series and was the only one that became widely used in medicine (although the racemic mix racemoramide saw some limited use). References Further reading Synthetic opioids 4-Morpholinyl compunds Pyrrolidines Carboxamides Mu-opioid receptor agonists Janssen Pharmaceutica Belgian inventions Benzhydryl compounds pl:Moramid