Inhibitors of the Thioesterase Activity of Mycobacterium tuberculosis Pks13 Discovered Using DNA-Encoded Chemical Library Screening.

DNA-encoded chemical library (DEL) technology provides a time- and cost-efficient method to simultaneously screen billions of compounds for their affinity to a protein target of interest. Here we report its use to identify a novel chemical series of inhibitors of the thioesterase activity of polyketide synthase 13 (Pks13) from Mycobacterium tuberculosis (Mtb). We present three chemically distinct series of inhibitors along with their enzymatic and Mtb whole cell potency, the measure of on-target activity in cells, and the crystal structures of inhibitor-enzyme complexes illuminating their interactions with the active site of the enzyme. One of these inhibitors showed a favorable pharmacokinetic profile and demonstrated efficacy in an acute mouse model of tuberculosis (TB) infection. These findings and assay developments will aid in the advancement of TB drug discovery.

Cognitive impairment following sedative overdose.

INTRODUCTION: Patients with sedative overdose may have residual cognitive impairment at the time they are deemed medically cleared for discharge. Impairment could affect the performance of high-risk activities, including driving. The Trail Making Test is an alpha-numeric assessment that can be performed at the bedside to assess cognitive function. We examined whether there were differences in cognitive function when medically cleared between patients that overdosed on sedative and non-sedative drugs. METHODS: A prospective, observational study assessed cognitive function using the Trail Making Test between 2018 and 2021. Patients (16 years and greater) completed testing upon medical clearance if they spoke English and had no previous neurological injury. Continuous covariates were compared using t-tests or Mann-Whitney U tests and multiple linear regression; binary variables were modelled using logistic regression. RESULTS: Of 171 patients enrolled, 111 (65 per cent) had sedative overdose; they were older (median 32.1 versus 22.2 years) and more likely to be male (58.6 per cent versus 36.7 per cent). Benzodiazepines and paracetamol were the commonest drug overdoses. Patients with sedative overdose performed worse on Trail Making Test part A (37.0 versus 33.1 seconds, P = 0.017) and Trail Making Test part B (112.4 versus 81.5 seconds, P = 0.004). Multiple linear regression analysis indicated that patient age (P < 0.001, 1.7 seconds slower per year, 95 per cent confidence interval: 0.9-2.6 seconds) and perception of recovery (P = 0.006, 36.4 seconds slower if perceived not recovered, 95 per cent confidence interval: 10.8-62.0 seconds) were also associated with Trail Making Test part B times. Patients with sedative overdose were more likely to be admitted to the intensive care unit (Odds Ratio: 4.9, 95 percent confidence interval: 1.1-22.0; P = 0.04). DISCUSSION: Our results are broadly in keeping with previously published work, but include a wider range of drug overdose scenarios (polypharmacy and recreational drugs). While patients demonstrated some perception of their cognitive impairment, our model could not reliably be used to provide individual discharge advice. The study design did not allow us to prove causation of cognitive impairment, or to make comparison between the strength of an overdose to the trail making test time. CONCLUSIONS: Trail Making Test results suggested that patients who had sedative drug overdoses may have significant cognitive deficits even when medically cleared. Risk of harm may be minimised with advice to avoid high-risk activities such as driving. More profound impacts seen on the Trail Making Test part B than A may mean higher-order thinking is more affected than simple cognitive function.

Common pitfalls in the use of hypertonic sodium bicarbonate for cardiac toxic drug poisonings.

BACKGROUND: Hypertonic sodium bicarbonate is advocated for the treatment of sodium channel blocker poisoning, but its efficacy varies amongst different sodium channel blockers. This Commentary addresses common pitfalls and appropriate usage of hypertonic sodium bicarbonate therapy in cardiotoxic drug poisonings. SODIUM BICARBONATE WORKS SYNERGISTICALLY WITH HYPERVENTILATION: Serum alkalinization is best achieved by the synergistic effect of hypertonic sodium bicarbonate and hyperventilation (PCO2 ∼ 30-35 mmHg [0.47-0.6 kPa]). This reduces the dose of sodium bicarbonate required to achieve serum alkalinization (pH ∼ 7.45-7.55) and avoids adverse effects from excessive doses of hypertonic sodium bicarbonate. VARIABILITY IN RESPONSE TO SODIUM BICARBONATE TREATMENT: Tricyclic antidepressant poisoning responds well to sodium bicarbonate therapy, but many other sodium channel blockers may not. For instance, drugs that block the intercellular gap junctions, such as bupropion, do not respond well to alkalinization. For sodium channel blocker poisonings in which the expected response is unknown, a bolus of 1-2 mmol/kg sodium bicarbonate can be used to assess the response to alkalinization. SODIUM BICARBONATE CAN EXACERBATE TOXICITY FROM DRUGS ACTING ON MULTIPLE CARDIAC CHANNELS: Hypertonic sodium bicarbonate can cause electrolyte abnormalities such as hypokalaemia and hypocalcaemia, leading to QT interval prolongation and torsade de pointes in poisonings with drugs that have mixed sodium and potassium cardiac channel properties, such as hydroxychloroquine and flecainide. THE GOAL FOR HYPERTONIC SODIUM BICARBONATE IS TO ACHIEVE THE ALKALINIZATION TARGET (∼PH 7.5), NOT COMPLETE CORRECTION OF QRS COMPLEX PROLONGATION: Excessive doses of hypertonic sodium bicarbonate commonly occur if it is administered until the QRS complex duration is < 100 ms. A prolonged QRS complex duration is not specific for sodium channel blocker toxicity. Some sodium channel blockers do not respond, and even when there is a response, it takes a few hours for the QRS complex duration to return completely to normal. In addition, QRS complex prolongation can be due to a rate-dependent bundle branch block. So, no further doses should be given after achieving serum alkalinization (pH ∼ 7.45-7.55). MAXIMAL DOSING FOR HYPERTONIC SODIUM BICARBONATE: A further strategy to avoid overdosing patients with hypertonic sodium bicarbonate is to set maximum doses. Exceeding 6 mmol/kg is likely to cause hypernatremia, fluid overload, metabolic alkalosis, and cerebral oedema in many patients and potentially be lethal. RECOMMENDATION FOR THE USE OF HYPERTONIC SODIUM BICARBONATE IN SODIUM CHANNEL BLOCKER POISONING: We propose that hypertonic sodium bicarbonate therapy be used in patients with sodium channel blocker poisoning who have clinically significant toxicities such as seizures, shock (systolic blood pressure < 90 mmHg, mean arterial pressure <65 mmHg) or ventricular dysrhythmia. We recommend initial bolus dosing of hypertonic sodium bicarbonate of 1-2 mmol/kg, which can be repeated if the patient remains unstable, up to a maximum dose of 6 mmol/kg. This is recommended to be administered in conjunction with mechanical ventilation and hyperventilation to achieve serum alkalinization (PCO2∼30-35 mmHg [4-4.7 kPa]) and a pH of ∼7.45-7.55. With repeated bolus doses of hypertonic sodium bicarbonate, it is imperative to monitor and correct potassium and sodium abnormalities and observe changes in serum pH and on the electrocardiogram. CONCLUSIONS: Hypertonic sodium bicarbonate is an effective antidote for certain sodium channel blocker poisonings, such as tricyclic antidepressants, and when used in appropriate dosing, it works synergistically with hyperventilation to achieve serum alkalinization and to reduce sodium channel blockade. However, there are many pitfalls that can lead to excessive sodium bicarbonate therapy and severe adverse effects.

Rivastigmine for the management of anticholinergic delirium.

INTRODUCTION: Anticholinergic agents are commonly taken in overdose, often causing delirium. The spectrum of anticholinergic delirium ranges from mild agitation to severe behavioural disturbance. Physostigmine is an effective treatment for anticholinergic delirium, but its availability is limited. As rivastigmine is readily available, it has been used to manage anticholinergic delirium; however, there is limited research investigating its use. METHOD: This was a retrospective review of patients with anticholinergic delirium treated in two toxicology units with rivastigmine (oral capsule or transdermal patch) from January 2019 to June 2023. The primary outcome was the use of further parenteral treatment (sedation or physostigmine) for delirium post rivastigmine administration. RESULTS: Fifty patients were administered rivastigmine for the management of anticholinergic delirium. The median age was 36 years (interquartile range: 25-49 years) and 27 (54 per cent) were females. Features consistent with anticholinergic toxicity included tachycardia in 44 (88 per cent) and urinary retention requiring catheterisation in 40 (80 per cent). Forty-three patients (86 per cent) were treated with physostigmine before rivastigmine administration. Twenty-two were managed with transdermal rivastigmine (most commonly 9.5 mg/24 hour patch), and 28 with oral rivastigmine 6 mg. Further parenteral sedation and/or physostigmine treatment were required more often in patients given transdermal than oral rivastigmine [16/22 (73 per cent) versus 9/28 (32 per cent), P = 0.010)]. No patients had bradycardia or gastrointestinal symptoms following rivastigmine administration. One patient with a history of epilepsy had a seizure, 1.5 hours post physostigmine administration and 7 hours post transdermal rivastigmine. DISCUSSION: Rivastigmine has been increasingly used for the management of patients with anticholinergic delirium, due to the lack of availability of physostigmine. In this case series, rivastigmine transdermal patch appeared to be less effective than oral rivastigmine capsules, likely due to its slow onset of action and/or insufficient dose. CONCLUSION: Rivastigmine can be used to treat anticholinergic delirium. In our case series oral rivastigmine appeared more effective than transdermal rivastigmine.

Home Therapies to Neutralize Button Battery Injury in a Porcine Esophageal Model.

STUDY OBJECTIVE: Button battery ingestion can cause alkaline esophageal injury. There is interest in first-aid household products to neutralize the injury. The objective was to investigate which household products are effective at reducing button battery injury. METHODS: Two cadaveric porcine experiments were performed. Experiment 1 utilized esophageal mucosal segments. A button battery (3VCR2032) was placed onto the mucosa, and substances (saline control, honey, jam, orange juice, yogurt, milk, and cola) were applied every 10 minutes for 6 applications. Tissue pH was measured every 10 minutes, and macroscopic ulceration size was assessed at 120 minutes. Experiment 2 used an intact esophageal model with a battery inserted into the lumen and jam, honey, and saline irrigation as per experiment 1. Tissue pH, macroscopic and histopathology changes were evaluated at 60, 90 and 120 minutes. RESULTS: In experiment 1, only honey and jam had a lower mean tissue pH at 120 minutes (8.0 [standard deviation [SD] 0.9, n=12] and 7.1 [SD 1.7, n=12], respectively) compared to saline solution 11.9 (SD 0.6, n=6, P<.0001). Both honey (0.24 cm2, SD 0.17) and jam (0.37 cm2, SD 0.40) had smaller mean areas of ulceration compared to saline solution (3.90 cm2, SD 1.03, P<.0001). In experiment 2, honey and jam had significantly lower mean tissue pH at all timepoints compared to saline solution. Histologic changes were evident at 60 minutes in the saline group, whereas honey and jam exhibited no or minimal changes until 120 minutes. CONCLUSIONS: Honey and jam were able to neutralize injury caused by a button battery resulting in a smaller area of ulceration. Jam should be further explored as a possible first-aid option as an alternative to honey in suspected button battery ingestion prior to definitive management.

Acetaminophen Metabolites on Presentation Following an Acute Acetaminophen Overdose (ATOM-7).

Acetaminophen (APAP) is commonly taken in overdose and can cause acute liver injury via the toxic metabolite NAPQI formed by cytochrome (CYP) P450 pathway. We aimed to evaluate the concentrations of APAP metabolites on presentation following an acute APAP poisoning and whether these predicted the subsequent onset of hepatotoxicity (peak alanine aminotransferase > 1,000 U/L). The Australian Toxicology Monitoring (ATOM) study is a prospective observational study, recruiting via two poison information centers and four toxicology units. Patients following an acute APAP ingestion presenting < 24 hours post-ingestion were recruited. Initial samples were analyzed for APAP metabolites, those measured were the nontoxic glucuronide (APAP-Glu) and sulfate (APAP-Sul) conjugates and NAPQI (toxic metabolite) conjugates APAP-cysteine (APAP-Cys) and APAP-mercapturate (APAP-Mer). The primary outcome was hepatotoxicity. In this study, 200 patients were included, with a median ingested dose of 20 g, 191 received acetylcysteine at median time of 5.8 hours post-ingestion. Twenty-six patients developed hepatotoxicity, one had hepatotoxicity on arrival (excluded from analysis). Those who developed hepatotoxicity had significantly higher total CYP metabolite concentrations: (36.8 µmol/L interquartile range (IQR): 27.8-51.7 vs. 10.8 µmol/L IQR: 6.9-19.5) and these were a greater proportion of total metabolites (5.4%, IQR: 3.8-7.7) vs. 1.7%, IQR: 1.3-2.6, P < 0.001)]. Furthermore, those who developed hepatotoxicity had lower APAP-Sul concentrations (49.1 µmol/L, IQR: 24.7-72.2 vs. 78.7 µmol/L, IQR: 53.6-116.4) and lower percentage of APAP-Sul (6.3%, IQR: 4.6-10.9 vs. 13.1%, IQR, 9.1-20.8, P < 0.001)]. This study found that those who developed hepatotoxicity had higher APAP metabolites derived from CYP pathway and lower sulfation metabolite on presentation. APAP metabolites may be utilized in the future to identify patients who could benefit from increased acetylcysteine or newer adjunct or research therapies.

Case series profile of olanzapine post-injection delirium/sedation syndrome.

Olanzapine pamoate is an intramuscular depot injection for the treatment of schizophrenia. Approximately 1.4% of patients develop a serious adverse event called post-injection delirium/sedation syndrome (PDSS), characterised by drowsiness, anticholinergic and extrapyramidal symptoms. The objective is to investigate olanzapine PDSS presentations including clinical features and treatment approach. This is a retrospective review of olanzapine PDSS patients from three toxicology units and the NSW Poisons Information Centre between 2017 and 2022. Adult patients were included if they had intramuscular olanzapine then developed PDSS criteria. Clinical symptoms, treatment, timing and length of symptoms were extracted into a preformatted Excel database. There were 18 patients included in the series, with a median age of 49 years (interquartile range [IQR]: 38-58) and male predominance (89%). Median onset time post injection was 30 min (IQR: 11-38). PDSS symptoms predominate with drowsiness, confusion and dysarthria. Median length of symptoms was 24 h (IQR: 20-54). Most common treatment included supportive care without any pharmacological intervention (n = 10), benzodiazepine (n = 4) and benztropine (n = 3). In one case, bromocriptine and physostigmine followed by oral rivastigmine were given to manage antidopaminergic and anticholinergic symptoms respectively. This proposed treatment combination could potentially alleviate some of the symptoms but needs further studies to validate the findings. In conclusion, this case series supports the characterisation of PDSS symptomology predominantly being anticholinergic with similar onset (<1 h) and duration (<72 h). Bromocriptine is proposed to manage PDSS if patients develop severe dopamine blockade and physostigmine followed by rivastigmine for anticholinergic delirium.

Tapentadol exposures and poisonings in Australia.

INTRODUCTION: Tapentadol is an atypical opioid with mu-receptor affinity and noradrenaline reuptake inhibition approved for use in Australia in 2011. However, data on tapentadol poisoning are scarce. OBJECTIVES: To investigate tapentadol poisonings and related deaths in Australia. METHODS: We performed a retrospective review of tapentadol poisonings from New South Wales Poisons Information Centre (NSWPIC) and three toxicology units in Australia. The National Coronial Information System (NCIS) database was searched to determine the number of tapentadol-related deaths. RESULTS: Between 2016 and 2020, 220 tapentadol calls were made to NSWPIC, with a 4.5-fold increase in tapentadol exposure calls. The median dose ingested was 575 mg (IQR: 300-1163 mg). Most overdoses included co-ingestions (75%), especially benzodiazepines (26%) and opioids (25%). From Jan 2016 to Dec 2021, 107 patients presented to the three toxicology units with tapentadol poisoning. The median dose ingested was 500 mg (IQR: 200-1400 mg). Most patients took co-ingestants (84%), including benzodiazepines (40%) and opioids (32%). Naloxone was administered in 39 patients (36%), 10 (9%) were intubated and the median length of stay was 18 h (IQR: 9-30). Thirty-five tapentadol-related deaths were recorded within NCIS between Jan 2015 and Oct 2021 with a median age of 51 years (IQR: 42-61 years). CONCLUSION: There are increasing tapentadol poisonings and deaths reported to the NSWPIC, three toxicology units, and NCIS in Australia. Most tapentadol poisonings were taken with benzodiazepines and/or other opioids.

Prescribing trend of tapentadol in a Sydney local health district.

AIMS: Tapentadol, an opioid with mu-opioid receptor agonism and noradrenaline reuptake inhibition, has been increasingly used in Australia since 2011. However, data on hospital prescribing trends and indications are scarce. This study aimed to investigate hospital prescribing trends of tapentadol, oxycodone and tramadol in a Sydney local health district (LHD) and the indications for tapentadol hospital prescriptions in an Australian tertiary hospital. METHODS: We analysed 5-year patient dispensing for tapentadol, oxycodone and tramadol from four hospitals in a Sydney LHD with data expressed as oral morphine equivalents (OME). We also conducted a retrospective review of 140 and 54 patients prescribed tapentadol at a tertiary hospital's surgical and spinal units in 2020. RESULTS: Over 5 years in the Sydney LHD, there was a 19.5% reduction in total dispensing of these opioids from 1 225 210 to 986 477.5 OME milligrams. Decreases were specifically for oxycodone (-37.8% immediate-release, -65.2% sustained-release) and tramadol (-74.6% immediate-release, -70.1% sustained-release). Contrastingly, hospital prescriptions of tapentadol immediate-release increased by 223.2% between 2018-19 and 2020-21 while sustained-release increased by 17.9% from 2016-17 to 2020-21. By 2020-21, tapentadol overtook oxycodone to become the most prescribed opioid in the Sydney LHD (51.4%). At the hospital's surgical units, 137 (97.9%) patients were prescribed tapentadol for acute post-operative pain with the majority (54.0%) prescribed both immediate-release and sustained-release tapentadol, while 71.1% were prescribed for neuropathic pain in the spinal units. CONCLUSION: In a Sydney LHD, tapentadol prescriptions increased significantly to become the preferred opioid analgesic. At the hospital's surgical units, off-label prescriptions of tapentadol sustained-release for acute post-operative pain were observed.

Overdose and take-home naloxone in emergency settings: A pilot study examining feasibility of delivering brief interventions addressing overdose prevention with 'take-home naloxone' in emergency departments.

OBJECTIVE: Although most unintentional opioid deaths in Australia are attributed to pharmaceutical opioids, take-home naloxone (THN) programmes have to date predominantly targeted people using illicit opioids in drug treatment and harm reduction settings. We sought to examine the feasibility of delivering THN brief interventions (THN-BIs) with intranasal naloxone in EDs. METHODS: This pilot feasibility study was conducted across three major metropolitan EDs in Sydney and Melbourne. ED staff were surveyed about their perspectives regarding THN before completing a 30-min training programme in THN-BI delivery. Patients presenting with opioid overdose or considered high risk for future overdose were eligible to receive the THN-BI. Staff survey responses were compared between hospitals and provider types using one-way analysis of variances. Patient demographic and clinical characteristics were extracted from medical records and compared between hospitals and overdose type using Fisher's exact test and one-way analysis of variances. RESULTS: One hundred and twenty-two ED staff completed the survey. One hundred and ten (90.2%) agreed that EDs should provide THN-BIs, whereas 23 (19.2%) identified time constraints and 17 (12.9%) felt uncomfortable discussing overdose with patients. Fifty-seven patients received the THN-BI, with the majority (n = 50, 87.7%) having presented following opioid overdose. The median age was 44 years and 40 (71.4%) were men. Two-thirds of the overdoses (n = 31, 66.0%) were attributed to heroin with one-third (n = 16, 34%) being attributed to pharmaceutical opioids. CONCLUSIONS: ED-based delivery of THN-BIs can reach a wide range of individuals at-risk of overdose. The present study supports the feasibility of THN interventions in EDs and underscores the importance of addressing implementation barriers including staff training.

Clinical experience with titrating doses of digoxin antibodies in acute digoxin poisoning. (ATOM-6).

INTRODUCTION: For acute digoxin poisoning, it has been recommended to give bolus doses of 10-20 vials or potentially larger than needed doses calculated from dose ingested or the measured concentration. However, a recent revision of internal Poisons Information Centre guidelines prompted a change of our recommendations, specifically instead of large boluses, to use titrating repeated low doses of digoxin antibodies(Digoxin-Fab) based on bedside assessment of cardiac toxicity. METHODS: This is a prospective observational study of patients with acute digoxin poisoning identified through two Poisons Information Centres and three toxicology units. Patient demographics, signs and symptoms of digoxin toxicity, doses and response to Digoxin-Fab, free and bound serum digoxin concentrations. Outcomes were recorded and analysed. RESULTS: From September 2013 to September 2020, 23 patients with 25 presentations (median age 56 years, females 56%) were recruited. Median dose ingested was 13 mg(IQR: 9.5-25). Median heart rate (HR) was 41 beats/min before treatment. Initial median digoxin and potassium concentrations were 14.5 nmol/L (IQR: 10.9-20) [11.2 µg/L(IQR: 8.4-15.4)] and 5 mmol/L (IQR: 4.5-5.4 mmol/L), respectively. Gastrointestinal symptoms and acute kidney injury were present in 22 patients (88%) and 5 patients (20%), respectively. Four patients received an initial bolus dose of Digoxin-Fab of 5-20 vials. Twenty-one patients received repeated titrated doses (1-2 vials) of Digoxin-Fab and the median total dose was 4 vials (IQR: 2-7.5). Median maximal change in HR post-Digoxin-Fab was 19 beats/min. The median potassium concentration decrease post-Digoxin-Fab was 0.3 mmol/L. Total dose used in the titration group was 25% and 35% of the predicted doses based on the amount of digoxin ingested or measured serum concentration, respectively. Twelve had free digoxin concentrations measured. Free digoxin concentrations dropped to almost zero after any dose of Digoxin-Fab. Ten patients had a rebound of digoxin >2.6 nmol/L (2 µg/L). There were no deaths from acute digoxin toxicity. CONCLUSIONS: The new practice of using small, titrated doses of Digoxin-Fab led to a considerable reduction in total usage and major savings. The clinical response to titrated doses was safe and acceptable in acute digoxin poisoning.

Optimising alkalinisation and its effect on QRS narrowing in tricyclic antidepressant poisoning.

AIMS: The objectives were to determine the effect of NaHCO3 and/or mechanical ventilation on the biochemical profile and serum alkalinisation in tricyclic antidepressant (TCA) poisoning and investigate the impact of effective alkalinisation therapy on the QRS interval in TCA poisoning. METHODS: This was a retrospective review of TCA poisonings from three Australian toxicology units and a poisons information centre (Jan 2013 to Jan 2019). We included patients with TCA toxicity who ingested>10 mg/kg or had clinically significant toxicities consistent with TCA poisoning, and analysed patients' clinical, electrocardiogram and biochemical data. RESULTS: Of 210 patients, 84 received NaHCO3 and ventilation (dual therapy), 12 NaHCO3 , 46 ventilation and 68 supportive care treatment. When compared with single/supportive groups, patients who received dual therapy had taken a significantly higher median dose of TCA (1.5 g vs1.3 g, P < .001), a longer median maximum QRS interval (124 ms, interquartile ranges [IQR] 108-138 vs106 ms, IQR 98-115, P < .001) and were more likely to have seizures (14% vs3%, P = .006) and arrhythmias (17% vs1%, P < .001). The dual therapy group demonstrated greater increases in serum pH (median 0.11, IQR 0.04-0.17) compared to the single/supportive therapy group (median 0.03, IQR -0.01-0.09, p < .001). A greater proportion of patients reached the target pH 7.45-7.55 in the dual therapy group (59%) compared to the single/supportive therapy group (10%) (P < .001). For each 100 mmol bolus of NaHCO3 given, the median increase in serum sodium was 2.5 mmol/L (IQR 1.5-4.0). QRS narrowing occurred twice as quickly in the dual therapy vs single/supportive therapy group. CONCLUSIONS: A combination of NaHCO3 and mechanical ventilation was most effective in achieving serum alkalinisation and was associated with a more rapid narrowing of the QRS interval. We advise that the maximal dose of NaHCO3 should be <400 mmol (6 mmol/kg).

Just 'nanging' around - harmful nitrous oxide use: a retrospective case series and review of Internet searches, social media posts and the coroner's database.

BACKGROUND: The chronic recreational inhalation of nitrous oxide (N2 O) 'nanging', can have adverse neurological and psychiatric effects. AIM: To evaluate cases of chronic N2 O use presenting to two hospitals, as well as to evaluate nationally N2 O deaths reported to the coroner and trends in Internet searches and social media posts related to N2 O. METHODS: Retrospective review of two toxicology units, from July 2017 to October 2020, of patients presenting with chronic N2 O use and neurological and/or psychiatric symptoms. We evaluated 10 years (2010-2019) of Internet search and social media trends involving N2 O and the National Coronial Information System (NCIS) database for deaths across Australia. RESULTS: Twenty-two patients were identified: median age 22 years, half female, 17 Asian background and 15 students. Presentations included decreased mobility or unsteady gait (n = 15) and psychiatric symptoms (n = 5). The median reported bulb use/day was 300 (interquartile range (IQR): 200-370), for a median of 6 months (IQR: 3-24). On magnetic resonance imaging, 10/18 had subacute combined degeneration of the spinal cord and 7/7 sensorimotor neuropathy on nerve conduction studies. All received high-dose intramuscular vitamin B12 and 11 methionine. Despite prolonged rehabilitation, nine required walking aids on discharge. Since 2017, social media posts and Internet searches for N2 O increased rapidly, the latter mostly directed at obtaining N2 O canisters. From the NCIS, 36 deaths were identified, 12 unintentional (recreational drug use), 20 intentional self-harm and 4 traumatic. CONCLUSION: We report a case series of symptomatic chronic N2 O use, many with ongoing neurological sequelae. Furthermore, a sharp increase in Internet searches to obtain N2 O cannisters was noted. Education of high-risk student groups on the long-term sequelae is important.