ibntxa ibntxa ibntxa, or 3-iodobenzoyl naltrexamine, is an atypical opioid analgesic drug derived from naltrexone. in animal studies it produces potent analgesic effects that are blocked by levallorphan and so appear to be μ-opioid mediated, but it fails to produce constipation or respiratory depression, and is neither rewarding or aversive in conditioned place preference protocols. these unusual properties are thought to result from agonist action at a splice variant or heterodimer of the μ-opioid receptor, rather than at the classical full length form targeted by conventional opioid drugs. ibntxaclinical dataatc codenoneidentifiers iupac name n-isoquinoline-7-yl]-3-iodobenzamide pubchem cid51003467chemspider26617995chemical and physical dataformulac27h29in2o4molar mass572.443 g·mol−13d model (jsmol)interactive image smiles c1c2(3cc4=c52(ccn3cc6cc6)(1nc(=o)c7=cc(=cc=c7)i)oc5=c(c=c4)o)o inchi inchi=1s/c27h29in2o4/c28-18-3-1-2-17(12-18)25(32)29-19-8-9-27(33)21-13-16-6-7-20(31)23-22(16)26(27,24(19)34-23)10-11-30(21)14-15-4-5-15/h1-3,6-7,12,15,19,21,24,31,33h,4-5,8-11,13-14h2,(h,29,32)/t19-,21-,24+,26+,27-/m1/s1key:fgafdgwrfojpry-xgtkutnfsa-n in the radioligand binding assay it has shown to have affinities of 0.11nm at the mor, 0.24nm at the dor and 0.03nm at the kor and in the hot- plate assay it is shown to be around 20x more potent than morphine. azido aryl analogues of ibntxa retain significant activity at the mor.