Not all that long ago I sampled clonitazene to see if that family is one which may have members which would make good candidates to make into multi-year pellets or load into implantable osmotic engines six months at a time but was very unimpressed -- I think we are seeing all of the problems with fentantils including potential intolerance, allergies, and some very un-narcotic-like subjective effects which could send chronic pain patients around the bend, just ask folks at Morton Thiokol about the sustainability of benzimidazoles, and similar troubles seem to arise with Bentley Compounds -- if 14-methoxymetopon and its derivatives turn out to have the same trouble, I think the folks working on these somewhat futuristic and wonderful ideas are going to be stuck . . .
Analogues of ketobemidone, piritramide, dipipanone & phenadoxone, dimenoxadole, and dextromoramide may be helpful . . . my few experiences some time ago with dimethylthiambutene and reading the literature make me think that branch of the open chain opioids may be restricted to veterinary use at least until the brave new world of Doctor Doolittle becomes reality and they start demanding heroin and dipipanone + cyclizine, as DMTB didn't feel that good and didn't relieve pain all that well, and the thiambutenes don't have favourable therapeutic indices and other statistics compared to other narcotics already out there . . .