Designer Benzodiazepines: A Review of Toxicology and Public Health Risks

The rising use of designer benzodiazepines (DBZD) is a cat-and-mouse game between organized crime and law enforcement. Non-prohibited benzodiazepines are introduced onto the global drug market and scheduled as rapidly as possible by international authorities. In response, DBZD are continuously modified to avoid legal sanctions and drug seizures and generally to increase the abuse potential of the DBZD. This results in an unpredictable fluctuation between the appearance and disappearance of DBZD in the illicit market. Thirty-one DBZD were considered for review after consulting the international early warning database, but only 3-hydroxyphenazepam, adinazolam, clonazolam, etizolam, deschloroetizolam, diclazepam, flualprazolam, flubromazepam, flubromazolam, meclonazepam, phenazepam and pyrazolam had sufficient data to contribute to this scoping review. A total of 49 reports describing 1 drug offense, 2 self-administration studies, 3 outpatient department admissions, 44 emergency department (ED) admissions, 63 driving under the influence of drugs (DUID) and 141 deaths reported between 2008 and 2021 are included in this study. Etizolam, flualprazolam flubromazolam and phenazepam were implicated in the majority of adverse-events, drug offenses and deaths. However, due to a general lack of knowledge of DBZD pharmacokinetics and toxicity, and due to a lack of validated analytical methods, total cases are much likely higher. Between 2019 and April 2020, DBZD were identified in 48% and 83% of postmortem and DUID cases reported to the UNODC, respectively, with flualprazolam, flubromazolam and etizolam as the most frequently detected substances. DBZD toxicology, public health risks and adverse events are reported.


Introduction
Benzodiazepines (BZD), important forensic and clinical toxicology drugs, are widely prescribed for neurological and psychiatric disorders and are also highly abused [1][2][3]. Discovered in the mid-1950s, BZD were designed as pharmacotherapies for anxiety, panic attacks, sleep disorders and epilepsy, and they have been used as myorelaxants during surgical and orthopedic procedures [4,5]. BZD are positive allosteric modulators that enhance the binding affinity of the inotropic γ-aminobutyric acid-A receptor (GABA A ) for GABA, the major central nervous system (CNS) inhibitory neurotransmitter [6,7]. Unlike GABA A agonists that work directly on the receptor, BDZ increase the frequency of GABA A channel opening, depending only on the endogenously available GABA [8][9][10]. Due to controlled neuronal inhibition and lower CNS depression risk, BZD rapidly replaced older medications such as barbiturates, meprobamate and chloral hydrate, becoming the most prescribed drug class in the world during the 1970s [11,12]. Although they possess a high therapeutic index, BZD also come with several side effects, such as drowsiness, dizziness,   EtOH blood 0.68 g/L BUP blood 1.1 ng/g, urine200 ng/g 3F-AMP blood 10 ng/g MAMP blood 190 ng/g AMP blood 1000 ng/g Blood 13 ng/g EtOH blood 1.9 g/L Blood 33 ng/g N-ethyl-3F-AMP blood screen + 3F-AMP blood screen +

Adinazolam
Adinazolam or 1-(8-chloro-6-phenyl-4H- [1,2,4]triazolo [4,3-a] [1,4]benzodiazepin-1-yl)-N,N-dimethylmethanamine is a short acting triazolo-BZD with anxiolytic, antidepressant, anticonvulsant and sedative properties [121,122]. Clinical studies revealed that drowsiness and dizziness are commonly observed after oral administration of adinazolam up to 70 mg, resulting in significant amnestic and psychomotor effects at higher doses [123][124][125]. Adinazolam was never FDA approved and never introduced onto the public market; however, it started to emerge as an illegal designer drug in 2015 [126,127]. The first reported adinazolam-related death concerned a young woman found dead in her apartment next to five resealable bags with unidentified powders/crystals. In the US, since April 2020, adinazolam was identified in at least three toxicology cases in association with etizolam, fentanyl and flualprazolam [128]. One male, one female and one unknown sex individual, all of whom were aged 20-40 years and each either from Michigan, Mississippi or Rhode Island, were the decedents. Adinazolam was identified in postmortem blood samples but was neither quantified nor listed as the cause of death. [1,4]benzodiazepine, also known as clonitrazolam, is the triazolo-analogue of clonazepam [1,129]. Clonazolam is described as "insanely powerful", producing strong sedation and amnesia at oral doses as low as 0.5 mg, resulting in easy accidental overdose [78]. It was found for the first time in seized yellow capsules by Swedish police on October 2014 and reported to the EMCDDA on January 2015 [51]. Two patients were admitted to ED after consuming clonazolam bought on the Internet. Clonazolam was not confirmed, and the dose was estimated based on the patient's self-report. In the other four cases, clonazolam or clonazolam and etizolam (one case) were identified. The primary adverse effect was CNS depression.

Deschloroetizolam
Deschloroetizolam is a short-acting thienotriazolodiazepine that differs from etizolam by the absence of a chlorine on the benzene ring with consequent reduced potency [1]. On 1 September 2014, the UK Focal Point reported that the substance was confirmed after analysis of a blue seized tablet [50]. There are few data available on deschloroetizolam. In a self-administration study, one of the authors ingested one-half pink tablet of deschloroetizolam, about 6 mg, bought on the Internet [79]. After 15 min, the subject's overall behavior changed rapidly; both physical and cognitive effects were described. Oral fluid was collected after 30 min. Deschloroetizolam and diclazepam's metabolites, lorazepam and lormetazepam, were detected in a young male. The subject was found dead with injection materials and several small plastic bags labelled with different DBZD [81].

Diclazepam
Diclazepam, or 2-Chlorodiazepam, is the 2'-chloro derivative of diazepam and the positional isomer of 4-chlorodiazepam [84]. It was reported to EMCDDA by Germany in August 2013 [49]. In two of three cases displayed, subjects were admitted to the ED in a severe state of agitation and disorientation; diclazepam was detected along with stimulants and dissociatives. In the third ED admission, diclazepam was the sole drug reported. Symptoms of intoxication were mainly characterized by CNS depression and a withdrawal syndrome. The patient reported having ingested two 30 mL vials of 4 mg/mL diclazepam (240 mg) purchased online. Again, 13 drivers apprehended for DUID submitted to a clinical test of impairment (CTI). The level of impairment was assessed based on the single test results and the individual's general condition. Common signs of impairment were found for alertness, appearance, cognitive function, motor coordination and vestibular function. Heide et al. report four additional DUID cases. Subjects were aged between 30 and 39 years; sex was not specified, and diclazepam was found in blood at concentration ranging from 5.4 ng/mL to 32 ng/mL [86]. The subjects did not show impairment. The only death reported involved a young man with a history of methamphetamine use found deceased at home. He previously told a friend that at times he took etizolam. Retrospective quantitative analysis revealed the presence of diclazepam and flubromazolam, along with opioids and stimulants. In addition, in 2013, a French patient was admitted to the ED after ingestion of two pills labelled "diclazepam" and "2-aminoindane" bought on the Internet. Upon clinical examination, the patient was anxious, but the anxiety resolved, and the patient was discharged the same day [130]. Diclazepam was neither confirmed nor quantified.

Etizolam
Etizolam, or 4-(2-chlorophenyl)-2-ethyl-9-methyl-6H-thieno[3,2-f ] [1,2,4]triazolo [4,3α] [1,4]diazepine, is a short-acting thienotriazoldiazepine introduced in 1983 under the trade name Depas ® [131,132]. It is currently used in India, Italy, Japan and Korea for the short-term treatment of insomnia, anxiety and panic attacks, but it is not approved for medical use elsewhere [55,71]. It was reported to EMCDDA in December 2011 by UK [133]. Three intoxications required ED admission. Three children were found drowsy and wobbly after eating colored pills thought to be candies. Etizolam was confirmed in one patient's urine. In addition, a subject was found unconscious next to a syringe of heroin. He had previously ingested a large quantity of etizolam tablets. Three patients with psychiatric disorders presented at an outpatient department for etizolam detoxification after exhibiting tolerance and withdrawal. Etizolam was prescribed or illegally obtained in one case and was taken at supratherapeutic doses. For six DUID cases, three were apprehended drivers undergoing CTI, while three drivers were stopped for impaired driving and underwent a standardized field sobriety test (SFST). These results supported the diagnosis of motor and functional impairment. The other two males, ages 34 and 19 years, underwent CTI [85]. Etizolam was found in blood at concentrations of 31 ng/mL and 120 ng/mL, respectively; however, impairment was impossible to determinate or not reported. A total of 34 deaths were reported. In five cases, etizolam was found in association with diclazepam, (one case), flubromazepam (one case), flubromazolam (two cases) and flualprazolam and flubromazolam in one case. In 33 cases the cause of death was reported as accidental overdose due to polydrug toxicity; subjects were known drug users or had a history of mental disorders. In the remaining case [92], the subject was found dead in the bathroom with a suicide note in her diary. In these nine cases [92,95,97], etizolam was detected in peripheral blood at concentrations of 1-237 ng/mL. Subjects were seven males and two females between 22 and 61 years of age, residing in Japan, the UK or the US. However, etizolam was not listed as the cause of death.

Flualprazolam
Flualprazolam is the ortho fluorine analogue of alprazolam that was reported to the EMCDDA by Swedish police in January 2018 [99]. Seven young patients were transported to the ED after ingesting a BZD thought to be alprazolam. Three patients exhibited sedation and verbal impairment, two CNS depression, and two were asymptomatic. In three cases the presence of flualprazolam was not confirmed. Another thirteen DUID cases were reported. One individual was subjected to the CTI while twelve other drivers underwent SFSTs. Considerable motor and functional impairment were observed. Two biological samples screened positive for etizolam. Furthermore, Papsun et al. reported an additional 11 DUID [101]; however, demographic information and flualprazolam blood concentrations were not available. A total of 38 deaths were reported. All cases had multiple drugs; one was also positive for etizolam. In 36, the cause of death was listed as accidental overdose due to multiple drug toxicity, while in 2 cases they were ruled intentional flualprazolam poisonings. Furthermore, there were 28 additional deaths in which flualprazolam was not listed as the cause of death; these include 5 decedents from Finland, 13 from Sweden and 10 from the US. Flualprazolam blood concentrations ranged from 3 ng/mL to 620 ng/mL [101,102].

Flubromazepam
7-Bromo-5-(2-fluorophenyl)-1,3-dihydro-2H-1,4-benzodiazepin-2-one, well known as flubromazepam, was detected for the first time in ten seized capsules in Germany and reported to the EMCDDA in March 2013 [49]. Four subjects were admitted to the ED in a profound state of agitation and delirium, followed by rigidity and CNS depression. In one case, flubromazepam's depressant effect was mitigated by the presence of methoxyphenidine. Only one DUID was reported. The driver was mildly impaired based on the CTI. Another apprehended, a 22-year-old driver, had a flubromazepam blood concentration of 7 ng/mL but did not show impairment on his CTI [86]. Only a single death case is included for flubromazepam. This young man was admitted to the ED in a severe state of CNS depression requiring resuscitation and mechanical ventilation; he died after six days of hospitalization. Flubromazolam and U-47700, which was also detected, were listed as the cause of death.

Flubromazolam
Flubromazolam is the triazolo-derivate of flubromazepam. It was identified in Sweden in 10 seized white tablets labelled "XANAX" and reported to EMCDDA in October 2014 [50]. It possesses strong and long-lasting depressive effect on the CNS. Eighteen patients were admitted to the ED in a severe state of CNS depression with functional and motor impairment. In 16 cases, flubromazolam was the sole drug detected, while in 2 cases subjects were also positive for meclonazepam. One patient required three days of hospitalization. After logical verbal contact was established, he admitted that he bought flubromazolam on the Internet and consumed about 3 mg approximately 19 h before ED admission [106]. Eleven flubromazolam DUID cases were reported; in two, driving impairment was assessed by CTI, while in the remaining nine, a SFST was performed by officers. Motor and functional impairment was evident in all subjects. Flubromazolam was listed as a contributory cause of death in four cases. Abdul et al. reported two additional deaths in which flubromazolam was found in femoral blood at concentrations of 8 and 16 ng/mL [108]. The two male decedents were 32 years old and 46 years old. The cause of death was not flubromazolam toxicity. Flubromazolam pharmacokinetics were assessed in a self-administration study. One of the authors ingested a 0.5 mg capsule of flubromazolam. During the following 24 h, the author observed strong sedation and considerable memory impairment.

Meclonazepam
Meclonazepam is structurally related to clonazepam and was reported for the first time to EMCDDA in August 2014 after identification in 145 seized capsules in Sweden [50]. A young man was admitted to the ED in December 2014 after ingesting approximately 100 tablets (600 mg) of meclonazepam. The subject was awake but not completely lucid.

Phenazepam and 3-Hydroxyphenazepam
Phenazepam, also known as "Bonsai", "Zannie" or "Supersleep", is a long-acting benzodiazepine developed in the 1970s and currently used as an anxiolytic, hypnotic and for the treatment of Alcohol Withdrawal Syndrome in the former USSR [134]. Phenazepam was reported to EMCDDA in July 2011 by Germany and UK. It is metabolized to the active metabolite 3-hydroxyphenazepam by different isoforms of CYP450 [114,135]. 3-Hydroxyphenazepam was identified in a seized white tablet and reported in October 2016 by Denmark. Three subjects were admitted to the ED after ingesting illicit phenazepam purchased on the Internet. Patients exhibited both motor and functional impairment and depressant effects. One patient had Asperger's syndrome [110]. In May 2016, a patient was admitted to the ED after ingesting four tablets of 3-hydroxyphenazepam. There also are 19 DUID and a drug offense cases included in Table 1. Of these, 11 underwent SFST, 5 had roadside drug tests, 3 CTI, while 1 driver refused to perform SFST, and symptoms of impairment were provided by the officer's observations. Moderate to considerable motor and functional impairments were evident in all drivers. Heide et al. reported one additional DUID of a young driver submitted for CTI [86] who also had a phenazepam blood concentration of 120 ng/mL. The driver passed his CTI and was declared not impaired. Of sixty deaths reported, phenazepam alone was listed as the sole cause of death in two cases, while the remaining were attributed to accidental overdose due to polydrug toxicity.

Pyrazolam
Pyrazolam is the triazolo analogue of bromazepam that was identified in Finland in 10 white tablets and notified to EMCDDA in August 2012 [136]. In February 2016, a young man was found dead in an advanced state of putrefaction next to five plastic bags labelled pyrazolam, diclazepam, 3F-phenmetrazine, 1-(2-fluorophenyl) propan-2-amine and diphenhydramine hydrochloride, as well as one unlabelled bag. Asphyxia promoted by polydrug intoxication was listed as the cause of death.

Discussion
Seventy percent of the new DBZD were introduced into the European Union (EU), representing about thirteen percent of worldwide NPS seizures [137]. The EU market is dominated by a handful of these, most notably clonazolam, diclazepam, etizolam, flualprazolam, flubromazolam and phenazepam [31,58,64,[138][139][140]. Etizolam, in particular, is the "street" BZD that is most often implicated in drug related deaths. In Scotland, its numbers grew from 223 in 2016 to 752 in 2019 [141]. DBZD are a worldwide growing public health concern. In the US, more than 5000 cases regarding clonazolam, etizolam and flualprazolam were reported in the US NFLIS from Federal, State and local laboratories between October and December 2020 [142]. The Center for Forensic Sciences Research and Education confirmed this trend for the first quarter of 2021, underlining the popularity of flubromazolam [143]. Etizolam, flualprazolam and flubromazolam were recently identified in counterfeit Xanax tablets in Canada, and their use is increasing also in Central and South America, mainly in Brazil, Chile and Paraguay [54,144]. Surprisingly, no updated data on DBZD are available from Asia, although most NPS are synthesized in this area of the world. However, a small number of DBZD may be sourced from companies in India, typically as finished medicinal products [54,[145][146][147].
According to the UNODC, the highest public health risk around the world is from etizolam, flualprazolam, flubromazolam and phenazepam [54,72]. DBZD are widely available on the Internet in different forms, i.e., blotters, liquids, pills, powders and tablets, and sold at low prices [148]. Etizolam and phenazepam are further diverted from the regulated market and illegally imported from those countries where they are licensed therapeutic drugs [138,149]. For most NPS placed under international control, the number of reports decreased rapidly the year after the scheduling decision [150]. However, for flualprazolam, phenazepam, flubromazolam and etizolam, enforcement was delayed two, five, seven and nine years, respectively, after formal notification [73]. The social harms produced by these drugs' long residence on the illicit market are characterized by an increasing rate of DBZD-related deaths, involvement of criminal activity, violence, risktaking behavior, suicide attempts and concurrent substance use disorders [151,152].
Only cases in which DBZD were the sole or a contributory cause of intoxication, impairment or death are included in Table 1, which evaluates global DBZD intake. This facilitates review of the biological concentrations in the different types of cases. Clinicians are unaware of DBZD and their contribution to drug overdoses and deaths, sometimes leading to incorrect interpretations of cause of death. Clinicians should be asking patients about substance abuse including NPS and DBZD during routine preventive care and ED visits. The patients may not be aware of the identity or concentration of DBZD in a drug product before suffering symptoms of intoxication [135]. When a DBZD is the only drug identified, it provides the opportunity to characterize its associated sedative-hypnotic toxidrome as seen in cases [45,74,77,79,80,82,[84][85][86][89][90][91]98,106,109,111,113,115].
However, since few pharmacokinetics studies were performed [82,109], it is currently hard to associate concentrations in biological matrices with presumable related adverseeffects. To date, correlations between dose and response, duration of action, metabolism, and onset of action are still poorly understood, making it harder for users to accurately dose the compound they purchased, increasing the prospect of potential intoxication. The slow elimination and the hepatic transformation in active metabolites of certain DBZD (i.e., flubromazolam and phenazepam) are responsible of their accumulation in lipid-based tissues, which can lead to a delayed overdose in cases of repeated consumption [44,82,91,152,153]. There was overlap between diclazepam, etizolam and phenazepam blood concentrations in impaired and non-impaired drivers [85,86]. Similarly, blood etizolam and flualprazolam concentrations were similar in DUID cases and deaths [86,92,101,102]. This may reflect differences in tolerance that appear after frequent drug exposure. In other cases, there is too little information or analytical data to improve our knowledge about the DBZD [74,83,104], and in many cases, because polypharmacy is the rule rather than the exception, it is not possible to assign causation to a single drug because the death is due to the drug combination [78,86,88,100,101,112]. On the other hand, it is also possible that many individuals exposed to DBZD never developed significant adverse events [154]. However, a major problem is knowing that in many cases the DBZD will never be detected due to a lack of analytical method capability or even just to unawareness of the presence of this class of NPS. Furthermore, the newest DBDZ may have high cross-reactivity with common BZD immunoassays, which often do not distinguish between designer and prescribed BZD. Metabolism to licensed BZD, the sale of metabolites of prescribed BZD and the unavailability of confirmatory testing in health care centers pose the risk of an incorrect interpretation of analytical findings [5,127,[155][156][157]. The roles DBZD play in deaths remains poorly understood, and how different pathologists and toxicologists attribute and interpret cause of death is largely unknown. For attributing the cause of death, each case must be assessed individually, taking into account the circumstances surrounding the death, drug tolerance and postmortem redistribution. [119,158,159]. The present data should inform interpretation of DBZD-related deaths and apprise law enforcement, clinicians and ED personnel on the dangers of DBZD.

Materials and Methods
31 DBZD were selected after consulting the UNODC Early Warning Advisory on NPS portal, the European Database on New Drugs, the US National Poison Data System and the Japanese Data Search System for NPS. Thereafter, a comprehensive literature search was performed using PubMed, Scopus, Google Scholar and Web of Science bibliographic databases to identify scientific reports on ED admissions, DUID and fatalities associated with DBZD use. Database-specific search features with truncations (represented by an asterisk) and multiple keywords (represented by quotation marks) were employed. The search terms employed were: acute, abuse, "access* to emergency department", "adverse effect*", diversion, "driving under the influence of drug*", DUID, fatal, "illegal market", intoxication*, lethal, misuse, overdose*, prescription, poison*, report*, schedule*, seizure* or traffic in combination with 3-hydroxyphenazepam, 4-chlorodiazepam, adinazolam, alprazolam triazolobenzophenone derivative, bentazepam, bromazolam, cinazepam, clobromazolam, cloniprazepam, clonazolam, deschloroetizolam, diclazepam, etizolam, flualprazolam, flubromazepam, flubromazolam, fluclotizolam, flunitrazolam, fonazepam, meclonazepam, metizolam, methylclonazepam, nimetazepam, nifoxipam, nitrazolam, norfludiazepam, norflunitrazepam, phenazepam, pyrazolam, thionordazepam or tofisopam. Further studies were retrieved from the reference list of selected articles and from reports from international institutions such as the World Health Organization (WHO), the EMCDDA, the US Drug Enforcement Administration (DEA) and the US Food and Drug Administration (FDA). Articles written in English and only one in Swedish were included. Databases were screened through March 2021 and references were independently reviewed by one of the authors to determine their relevance to the present article.

Conclusions
The outbreak of DBZD is a rising health and social concern. Clinical and forensic toxicologists are on the front line, in cooperation with public health safety institutions, to identify emerging DBZD in cases of intoxication, drug offenses and unexplained deaths. In order to decrease the availability of these substances in the global illicit drug market, more effort is needed by early warning agencies to reduce the timing between formal notifications and scheduling decisions. Further studies, professional training and analytical development are required to reduce the undercounting and underreporting of the cases in order to obtain robust and consistent epidemiological data.

Data Availability Statement:
No new data were created or analyzed in this study. Data sharing is not applicable to this article.

Conflicts of Interest:
The authors declare no conflict of interest.