A new group of potent synthetic opioids called nitazenes has been recognized as a growing threat. This review of the emerging case reports (published 2 months ago with fairly stringent inclusion criteria, and is the only one in existence) found that:
patients required doses of naloxone ranging from 1-6 mg
admission rates were 33-78%
the LOS ranged from 20 hrs for protonitazene to 360 hrs for metonitazene
nearly a quarter of the patients died
However, this prospective series out of Australia demonstrated a much milder picture of clinical burden, with a median IV naloxone dose of 0.4 mg and a median LOS of 17 h. However, this is likely attributable to expected geographic variation of the supply, as protonitazene was most commonly detected in this study, while was only rarely found in the previous scoping study (where it was also linked to the shortest mean LOS of 20 hrs).
Perhaps unsurprisingly, the latter article points out that most patients were not aware they were taking nitazenes, and co-ingestants were present in 97% (mostly methamphetamine).