Nifoxipam

Nifoxipam is a benzodiazepine and an active metabolite of flunitrazepam, also known as 3-hydroxydesmethylflunitrazepam. It appeared on the new psychoactive substance market in Europe in the mid-2010s, where it was detected in powders and tablets. Unlike many designer benzodiazepines, it is not simply a new synthetic analogue: it is a metabolite already formed by the human body after exposure to flunitrazepam.

Chemistry and relationship to flunitrazepam

Nifoxipam retains the fluorophenyl and nitrobenzodiazepine structure of flunitrazepam, but lacks the N-methyl group and carries a hydroxy group at the 3-position of the diazepine ring. This makes it one of the active metabolites formed during flunitrazepam metabolism, alongside compounds such as fonazepam.

Nifoxipam was identified in seizures of powders and tablets in Europe between 2014 and 2016. Its appearance as a separate product led forensic researchers to examine whether benzodiazepine metabolites could circulate as drugs in their own right (Katselou and colleagues, 2017).

Pharmacology

Direct pharmacological data on nifoxipam are limited. Because it is an active metabolite of flunitrazepam, similar benzodiazepine activity is expected. It is presumed to bind to the benzodiazepine site of the GABA_A receptor, enhancing inhibitory neurotransmission and producing sedative and anxiolytic effects.

Animal data summarised in the available literature describe tranquilising and sleep-prolonging effects. However, the evidence is not sufficient to establish a human potency comparison with flunitrazepam or other benzodiazepines.

Reported effects

The PsychonautWiki profile of nifoxipam describes strong tranquillising and sleep-promoting effects, although information is limited. Most expectations about its effects come from its relationship to flunitrazepam.

Likely benzodiazepine-class effects include reduced anxiety, sedation, muscle relaxation, impaired coordination and memory disruption. Reliable human reports are too scarce to establish how prominent each effect is or how nifoxipam differs from its parent compound.

Metabolism and forensic findings

Because nifoxipam is already a metabolite of flunitrazepam, its presence in a biological sample can reflect either direct exposure or metabolism of the parent drug. This distinction is important in forensic interpretation. A review of nifoxipam and fonazepam noted that, at the time of publication, no intoxication cases attributed specifically to either metabolite had been described in the scientific literature (Katselou and colleagues, 2017).

Later analytical work detected nifoxipam in urine samples from routine testing and emergency-department investigations. A study of glucuronidation found that nifoxipam conjugates could be detected in pooled human liver microsomes, although the responsible enzyme pathway was not fully resolved (Bergstrand and colleagues, 2019).

Toxicity and research limitations

There is no well-established human toxic range or clinical safety profile for nifoxipam. Its pharmacological effects are expected to resemble those of other benzodiazepines, but direct clinical evidence is sparse. Detection in toxicology samples confirms exposure but does not establish that nifoxipam was responsible for the symptoms in each case.

As with other benzodiazepines, combining nifoxipam with opioids, alcohol or other central nervous system depressants may increase sedation and respiratory depression. Dependence and withdrawal are plausible class-related concerns, but have not been quantified for nifoxipam itself.

Related compounds

Nifoxipam is related to Flunitrazepam and Fonazepam, both of which are part of the same metabolic pathway. It should be distinguished from flunitrazolam, which is a separate triazolobenzodiazepine.