In recent years the use of 2-benzylbenzimidazole opioids (\'nitazenes\') has increased with them becoming one of the most prominent synthetic opioid subclasses of novel psychoactive substances. With the increased prevalence there is also a concern of the dangers to public health with the use of nitazenes due to their high potency especially with polypharmacy. To aid in the detection of such compounds it is important that forensic toxicology laboratories maintain up-to-date compound libraries for drug screening methods and that sensitive analytical instrumentation is available to detect the low blood/plasma concentrations of more potent drugs. This includes not only the compounds themselves but also potential metabolites and/or degradation products. Metonitazene is a \'nitro-nitazene\' with a nitro group at position 5 of the benzimidazole ring. As a nitro-nitazene there is a potential for bacterial degradation of metonitazene to 5-aminometonitazene, as occurs with nitro-benzodiazepines. In this study we provide evidence from a post-mortem case of degradation of metonitazene in unpreserved post-mortem blood using LC-QQQ-MS, and putative identification of the degradation/ metabolic products 5-aminometonitazene and 5-acetamidometonitazene by LC-QTOF-MS. The results from LC-QQQ-MS analysis indicated that there did not appear to be such degradation in preserved (fluoride/oxalate) blood. These results suggest that nitro-nitazenes may be subject to similar in vitro stability/degradation issues as nitro-benzodiazepines. These breakdown products should be added to instrument libraries to aid in the detection of the use of nitro-nitazenes, and nitro-nitazenes should be quantified in preserved blood samples where available.