I've had it (UK) didn't know it had been discontinued, when was that?
I found it disgusting stuff. Interesting pharmacologically, in that it is a selective agonist for the MOR1 isoform of the MOR receptor, partial agonist, I'd say stronger than codeine but I couldn't tolerate it. It did a real number on my guts and left me doubled over in pain. Thinking this might be due (it happened even in opioid withdrawal so I think perhaps inherent to the properties of the drug itself, whereas a partial agonist would have made me feel better by some at least in full WD), but thinking it may be due to the bare phenolic moiety, the propionyl and benzoyl phenolic esters were tried, which, well to sum it up, only one of the two got tried, forget which as this was nearly 6 years ago maybe 7. And both the rest of it, and the other ester were chucked out.
They used it as a stronger than codeine alternative here, for those who couldn't take morphia or its relatives and were nontolerant and so fent etc. couldn't be used. My former housemate was scripted it and I seized all she had when i kicked her to the curb to experiment on and with. Nothing good ever came of it and all projects were scrapped. (if anyone was wondering about the housemate, she had it coming, she was a borderline PD bitch from fucking hell, who stole and hoarded my meds to try and make me go into WD, and then try to control me through controlling access to her own meds. Eventually she made at least one, probably two and possibly three attempts on my life, after which of course I kicked her ass out with nothing but the clothes on her back and an asthma inhaler thrown at her, after she tried outright, to gut me with a katana, only to find herself facing a swordsman more skilled than she, disarmed and beaten senseless. Had stolen money from my family, made false rape claims against not me, but two or three other people just to get an advantage over them and get things out of them. Real dirtbag, so as I saw it any of her possessions, once I had kicked her out, were mine for the taking as I saw fit, for she had no rights as a person, for a person she was and is not)
Bugger meptazinol and its esters though. Not worth the reagents it took to make them or the effort taken to recrystallize the stuff.
Longer action? trust me, you don't want longer acting meptazinol. It might well leave you doubled over in the foetal position begging for it to stop.