Penthrox enables quicker management of fractures, dislocations and more: learning lessons from expedited care of trauma patients during the COVID-19 pandemic

INTRODUCTION

Methoxyflurane is an historical anaesthetic agent that has undergone a renaissance with the introduction of a smaller dose in a handheld 'Penthrox' device. The benefits of Penthrox include its ease of use, with disposable individual packets, and the need for less monitoring and staff, when compared with deeper sedation. The literature acknowledges its use for analgesia and in the management of anterior shoulder dislocation but in no other procedural orthopaedic circumstance.

METHODS

Following institutional approval, we undertook a retrospective review of all incidences of Penthrox use to facilitate minor procedures within a 2-month period starting 24 March 2020. Time to procedure and success were recorded using the surrogate markers of patient attendance and x-Ray occurrence times.

RESULTS

Some 101 Penthrox doses were given to 89 patients over 97 unique episodes between 24 March and 26 May 2020. No complications were recorded following the use of Penthrox during this period. Patient demographics were explored. Fracture manipulations and casting (n=54) had a 100% success rate in achieving adequate and safe reduction. Joint dislocations (n=34) were treated with varying success. Native elbow dislocations were reduced most successfully (4/4, 100%). Native shoulder dislocations were seen in 17 patients and successful relocation was seen in 11 cases, giving a success rate of 65%.

CONCLUSIONS

This is the first study, outside anterior shoulder dislocations, to report on the efficacy of Penthrox within emergent orthopaedic scenarios. We have demonstrated Penthrox to be a safe tool for helping to manage trauma procedures in the emergency department.

Literature review on the use of methoxyflurane in the management of pain in cancer-related procedures

INTRODUCTION

Self-administered methoxyflurane, also known as Penthrox, at a sub-anesthetic dose is a short-term, fast-acting, and safe analgesic that may provide suitable pain relief for cancer patients. This review aims to compile the existing evidence on methoxyflurane and its efficacy in reducing pain during cancer-related procedures.

METHODS

A literature search was conducted through OVID Medline and Embase. The search was limited to articles published between 2012 and 2021 and studies were included if they assessed the efficacy of methoxyflurane to reduce pain in cancer-related procedures. All types of cancer were included.

RESULTS

The literature search yielded seven studies published between 2012 and 2021. The studies analyzed assessed methoxyflurane use in prostate biopsy, colonoscopy, removal of brachytherapy rods, and bone marrow biopsy. Various research designs were employed, including three randomized controlled trials, two prospective observational studies, one retrospective, and one non-randomized controlled trial. In all, methoxyflurane has a demonstrated ability to reduce pain in these procedures.

CONCLUSION

In the limited studies available in evaluating the efficacy of methoxyflurane for reducing procedural pain during cancer-related procedures, all have demonstrated clinical equivalency or superiority. Pain relief appears to be equivalent however methoxyflurane overcomes the standard limitations of respiratory sedation and has demonstrated quicker procedural recovery times than traditional sedation methods. The accumulated data to date supports the use of methoxyflurane which can supplement or supplant current methods of analgesia in cancer-related procedures.

How I Do It: Penthrox in Urology

Penthrox is a portable handheld inhaler that delivers a low dose of methoxyflurane - an anesthetic with analgesic effects, rapid onset of action, and a favorable side-effect profile. It has been widely used for acute pain management in Australia for the past 40 years. Currently, it is approved for use in over 55 countries, including Canada. Prospective randomized studies highlight Penthrox analgesic effectiveness and safety profile for emergency, prehospital and outpatient settings. In addition, the use of multimodal analgesia, specifically Penthrox, can play an important role in the analgesic management of urological procedures, such as prostatic biopsies and office-based minimally invasive surgical therapies. Herein readers will familiarize themselves with Penthrox, significant studies, and technique used for outpatient urological procedures.

Efficacy and safety of methoxyflurane (Penthrox) for pain control during water vapor thermal therapy (Rezum) for benign prostatic enlargement

INTRODUCTION

The safety and efficacy of low dose methoxyflurane disposable inhaler (Penthrox) was assessed in this study of men undergoing Rezum water vapor thermal therapy (WVTT).

MATERIAL AND METHODS

An open-labeled, single-center study was conducted to demonstrate the safety and efficacy of using methoxyflurane inhaler during a Rezum procedure. Patients assessed current pain intensity using a 10-point Visual Analog Scale (VAS) of Pain at 4 timepoints including (1) before any medication, (2) initially after insertion of the rigid cystoscope and before any Rezum treatment, (3) immediately after final injection of Rezum treatment and (4) at discharge. Patients were asked to fill out the Treatment Satisfaction Questionnaire for Medication (TSQM 1.4) and one question about pain relief at discharge. Treating physician also completed the TSQM 1.4.

RESULTS

Ten patients were recruited. Median prostate volume was 53.4 cc (range 24-158 cc). Patients received a median of 10.5 Rezum injections, with a median procedure time of 4.5 minutes. Median VAS scores were 0, 0.1, 0 (primary efficacy outcome) and 0 (out of scale of 10) at the 4 timepoints, respectively. TSQM scores on effectiveness, side effects, convenience and global median satisfaction rated by patients were respectively 69.4, 100.0, 77.8 and 82.1 (out of scale of 100). Treatment satisfaction on pain relief was rated as 4.0 (very good). There were no observed adverse events.

CONCLUSIONS

Methoxyflurane inhaler (Penthrox) was low cost, rapid, feasible and easy to administer as a pain management strategy for Rezum therapy. Further data from a larger comparative study will be conducted.

Pain management with methoxyflurane (Penthrox®) in Swedish ambulance care - An observational pilot study

BACKGROUND

In ambulance care, patients are often classified as high-risk, particularly when they are in immediate need of pain relief. It has been shown that, after ambulance nurses administer intravenous analgesic drugs, patients delivered to the emergency department tend to complain of moderate to severe pain.

AIMS AND OBJECTIVES

The present study aimed to evaluate the overall patient-perceived pain during treatment with methoxyflurane (MTX) in an ambulance-care setting. We also explored potential demographic variations.

METHODS

This prospective observational study included 50 patients in need of ambulance care that perceived acute pain, defined as a Numeric Rating Scale (NRS) value ≥4 (scale range: 1-10). We monitored the vital parameters of patients and MTX treatment characteristics, including the total number of inhaled MTX breaths and the average number of treatment sequences.

RESULTS

Among the 50 patients initially assessed, we excluded 8 patients (16%), due to MTX contraindications. We excluded 10 patients (24%), due to discontinued treatment. The remaining cohort (n = 32) that fulfilled the pain-relieving procedure, included equal numbers of men and women. The average time spent in ambulance care was 29 ± 15 min. The NRS scores for pain measured at the scene (median 8.0, interquartile range [IQR]: 7.25-10.0) were significantly higher than those measured at hospital admission (median 5.0, IQR: 4.0 7.0; p = .001). The median NRS scores measured at the hospital were different between sexes (men: 6.0, IQR: 5-7.25; women: 4.0, IQR: 3.76-6.0; p = .036). The average number of treatment sequences was 2. The overall average number of inhaled breaths was 17 ± 9.

CONCLUSION

This study demonstrates that MTX provided clinically significant lower pain scores among patients in ambulance care without significant effects on vital parameters. However, the pharmacological characteristics of MTX appeared to affect the potential of achieving standardized treatment objectives.

Inhaled methoxyflurane (Penthrox) for analgesia in trauma: a systematic review protocol

BACKGROUND

More than 75% of patients presenting to the Emergency Department are suffering symptoms of pain. Despite this, 67% will not receive any analgesia. Methoxyflurane is a fluorinated hydrocarbon gas which has analgesic properties when inhaled. Penthrox is a methoxyflurane autoinhaler recently licenced in Europe. Its ease of administration, safety, and fast onset of action make it of particular relevance to emergency medicine. Additionally, outside the hospital, it has the advantage of increased temperature stability and portability over current standard care. New evidence of its efficacy is emerging; however, currently, its use in Europe is not widespread. The objective of this study will be to systematically evaluate the evidence on inhaled methoxyflurane to determine if it is a superior analgesia in the acute trauma setting.

METHODS

We designed and registered a study protocol for a systematic review and meta-analysis on randomised controlled trials, comparing inhaled methoxyflurane and either placebo or standard care. A comprehensive search will be conducted from database inception onwards in MEDLINE, Embase, and the Cochrane CENTRAL database, concurrent with a search of the grey literature for other relevant studies, including clinical trial databases. Only randomised controlled trials will be included. No limitations will be imposed on publication status or language of publication. The primary outcome will be mean difference in patient-reported pain at time points within the first 30 min of administration. Secondary outcomes will be mean difference in time to clinically significant pain relief and relative risk of adverse effects. Two reviewers will independently screen all returned studies and collect data. Disagreements will be resolved through discussion or referral to a third reviewer. Individual study methodological quality will be appraised using an appropriate tool. If feasible, we will conduct a random effects meta-analysis; if this is not possible, we will construct a narrative synthesis.

DISCUSSION

This systematic review will summarise the best available evidence and definitively establish if inhaled methoxyflurane is a superior analgesia to standard care in the acute trauma setting. This knowledge will directly impact emergency care in the UK and worldwide and may require amendments to European pain relief guidelines.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42020189119 .

Service Evaluation of Methoxyflurane Versus Standard Care for Overall Management of Patients with Pain Due to Injury

INTRODUCTION

Inhaled methoxyflurane is an analgesic used for the emergency relief of moderate to severe pain in conscious adult patients with trauma and associated pain that is increasingly being used in hospital emergency departments to provide rapid analgesia. It is widely accepted that effective pain relief can facilitate patient care and flow through the emergency department (ED). The main aim of this evaluation was to assess the impact of inhaled methoxyflurane on patient length of stay (LOS) in the ED compared with standard care.

METHODS

Adult patients with moderate to severe trauma pain and Glasgow coma score of 15 were included in the evaluation. Evaluation forms were completed for 79 patients who received methoxyflurane and were matched with 80 patients who received standard care.

RESULTS

Overall the mean time spent in the ED was reduced by 71 min in those patients who were administered methoxyflurane compared with patients who received standard care. Furthermore, analysis of LOS by injury type demonstrated a reduction in ED LOS by 183 min for patients with shoulder dislocation who were treated with methoxyflurane compared with patients who received standard care. There was no reduction in ED LOS for patients with lower limb, hip or pelvic injuries between the two treatment groups.

CONCLUSION

Use of methoxyflurane in adult patients with trauma pain significantly reduced the ED LOS and may potentially improve patient flow through the ED.

Comparison of inhalational methoxyflurane (Penthrox®) and intramuscular tramadol for prehospital analgesia

INTRODUCTION

Treatment of pain is an important component of prehospital care. Inhalational analgesia agents have attractive strengths, but there is a paucity of studies comparing these with more conventional agents. We aimed to compare inhalational methoxyflurane and intramuscular (IM) tramadol as first-contact analgesia in the Singapore national ambulance service.

METHODS

Ambulances were randomised to carry either methoxyflurane or IM tramadol for the first six months and crossed over to the other arm after six months. Patients aged ≥ 16 years, with acute pain arising from musculoskeletal trauma with Numerical Rating Scale (NRS) score ≥ 3 were enrolled. Variables included NRS reduction, time variables, adverse effects, Ramsay Sedation Scores, and patient and paramedic satisfaction scores on a Likert scale.

RESULTS

A total of 369 patients were enrolled into this study, but 26 patients were excluded due to missing data. The methoxyflurane arm had a shorter median time taken from arrival at the scene to drug administration (9.0 [interquartile range 6.0-14.0] minutes vs. 11.0 [interquartile range 8.0-15.0] minutes). For patients who achieved reduction in NRS ≥ 3 within 20 minutes, those in the methoxyflurane arm took a shorter time. However, the methoxyflurane (46.7%) arm experienced lower proportion of patients not achieving NRS reduction ≥ 3 when compared to the tramadol (71.6%) arm after over 20 minutes. The methoxyflurane arm had significantly higher paramedic and patient satisfaction scores.

CONCLUSION

For the doses of medication used in this implementation study, methoxyflurane was superior in efficacy, speed of onset and administration, but had more minor adverse effects when compared to IM tramadol.

Analgesic Efficacy, Practicality and Safety of Inhaled Methoxyflurane Versus Standard Analgesic Treatment for Acute Trauma Pain in the Emergency Setting: A Randomised, Open-Label, Active-Controlled, Multicentre Trial in Italy (MEDITA)

INTRODUCTION

Inhaled low-dose methoxyflurane is approved in Europe for emergency relief of moderate-to-severe trauma-related pain in adults, but data versus active comparators are sparse. The phase IIIb Methoxyflurane in Emergency Department in ITAly (MEDITA) trial investigated the analgesic efficacy, practicality and safety of methoxyflurane versus standard analgesic treatment (SAT) for acute trauma pain.

METHODS

This was a randomised, active-controlled, parallel-group, open-label trial conducted in 15 Italian emergency units. Adults with limb trauma and pain score ≥ 4 on numerical rating scale (NRS) were randomised 1:1 to inhaled methoxyflurane 3 mL or SAT [intravenously administered (IV) morphine 0.1 mg/kg for severe pain (NRS ≥ 7); IV paracetamol 1 g or IV ketoprofen 100 mg for moderate pain (NRS 4-6)]. The primary endpoint was overall change in visual analogue scale (VAS) pain intensity from baseline (time of randomisation) to 3, 5 and 10 min. Non-inferiority and superiority of methoxyflurane versus SAT were concluded if the upper 95% confidence interval (CI) for the treatment comparison (methoxyflurane-SAT) was less than 1 and less than 0, respectively.

RESULTS

Between 8 February 2018 and 8 February 2019, 272 patients were randomised (136 per treatment group). A total of 270 patients (mean age 51 years; 49% male; 34% with severe pain; mean baseline VAS 67 mm) were treated and analysed for efficacy and safety. Superiority of methoxyflurane was demonstrated for moderate-to-severe pain (adjusted mean treatment difference - 5.94 mm; 95% CI - 8.83, - 3.06 mm), moderate pain (- 5.97 mm; 95% CI - 9.55, - 2.39 mm) and severe pain (- 5.54 mm; 95% CI - 10.49, - 0.59 mm). Median onset of pain relief was 9 min for methoxyflurane and 15 min for SAT. Practicality of methoxyflurane treatment was rated "Excellent", "Very Good" or "Good" by 90% of clinicians vs. 64% for SAT. Adverse events (all non-serious) were reported by 17% of methoxyflurane-treated patients and 3% of SAT-treated patients.

CONCLUSION

Methoxyflurane provided superior pain relief to SAT in patients with moderate-to-severe trauma pain and may offer a simple, fast, effective non-opioid treatment option.

TRIAL REGISTRATION

Trial registered with EudraCT (2017-001565-25) on 2 March 2018 and ClinicalTrials.gov (NCT03585374) on 13 July 2018.

FUNDING

Mundipharma Pharmaceuticals S.r.l.

Low-dose methoxyflurane analgesia in adolescent patients with moderate-to-severe trauma pain: a subgroup analysis of the STOP! study

Introduction

The undertreatment of acute pain presents a significant challenge in the Emergency Department. This post hoc subgroup analysis of a previously reported randomized controlled UK study reports the efficacy and safety of low-dose methoxyflurane analgesia in treating adolescent patients with moderate-to-severe trauma pain.

Patients and methods

Three hundred patients (96 in the adolescent subgroup) aged ≥12 years requiring analgesia for acute trauma pain (pain score of 4-7 on the Numerical Rating Scale) at triage were randomized 1:1 to methoxyflurane (up to 6 mL) or placebo (normal saline), both administered using a Penthrox^® inhaler. The patient could request rescue medication (paracetamol/opioids) at any time. The primary endpoint was the change from baseline in visual analog scale (VAS) pain intensity.

Results

Mean VAS pain score for the adolescent subgroup at baseline was ~ 61 mm. Adjusted mean change in VAS pain intensity from baseline to 5, 10, 15, and 20 minutes was -24.5, -28.1, -31.6, and -31.7 mm for methoxyflurane and -14.6, -18.8, -19.2, and -23.7 mm for placebo, with a statistically significant treatment effect in favor of methoxyflurane overall across all four time points (-9.9 mm; 95% CI: -17.4, -2.4 mm; P=0.0104). Median time to first pain relief was significantly shorter with methoxyflurane (1 minute) than placebo (3 minutes, P<0.0001). Pain relief was reported within 1-10 inhalations in 95.7% of methoxyflurane-treated patients and 64.6% of placebo-treated patients. Rescue medication was requested by two (4.3%) methoxyflurane-treated patients and three (6.3%) placebo-treated patients. Over 95% of patients, physicians, and nurses rated methoxyflurane treatment as "Excellent", "Very Good" or "Good" compared with between 64% and 68% for placebo. The incidence of adverse events was higher with methoxyflurane (51%) than placebo (42%), mostly comprising mild/transient dizziness and headache.

Conclusion

This subgroup analysis shows that low-dose inhaled methoxyflurane is a rapid-acting and effective analgesic in adolescent patients presenting with moderate-to-severe trauma pain.

Trial registration

Clinicaltrials.gov identifier: NCT01420159, EudraCT number: 2011-000338-12.

Penthrox: a breath of PHEC air for the military?

Prehospital analgesia is vital to good clinical care and inhaled methoxyflurane (Penthrox) would be a valuable addition to the armed forces medical armoury. Penthrox would provide strong, fast-acting, self-administered and safe analgesia to patients with moderate to severe injuries. In addition, it would provide an option for strong analgesia which would not be subject to the regulations that govern controlled or accountable drugs which gives it a unique position as the military moves its focus from large enduring operations to small short-term training teams supported by lone combat medics in remote locations across the globe.

Methoxyflurane Versus Standard of Care for Acute Trauma-Related Pain in the Emergency Setting: Protocol for a Randomised, Controlled Study in Italy (MEDITA)

Introduction

Low-dose methoxyflurane, administered via a hand-held inhaler, has been used for short-term pain relief in emergency medicine in Australia and New Zealand for over 40 years, and was recently approved in Europe for the rapid relief of moderate-to-severe trauma-related pain in adults. There is currently a lack of data for methoxyflurane versus active comparators, therefore this trial will investigate the efficacy and safety of inhaled methoxyflurane compared with standard of care (SoC) in the treatment of acute trauma-related pain in pre-hospital and ED settings in Italy.

Methods

MEDITA (Methoxyflurane in Emergency Department in ITAly) is a Phase IIIb, prospective, randomised, active-controlled, parallel-group, open-label, multicentre trial. A total of 272 adult patients with moderate-to-severe pain [score ≥ 4 on the Numerical Rating Scale (NRS)] due to limb trauma will be randomised 1:1 to receive 3 mL methoxyflurane (self-administered by the patient via inhalation under supervision of a trained person) or medications that currently comprise the SoC in Italy [intravenous (IV) morphine for severe pain (NRS ≥ 7); IV paracetamol or ketoprofen for moderate pain (NRS 4–6)], administered as soon as possible after randomisation.

Planned Outcomes

Pain intensity will be measured using a 100-mm visual analogue scale (VAS) at baseline (time of randomisation) and at intervals up to 30 min. Time of onset of pain relief as reported by the patient and use of rescue medication will be recorded. The patient will rate the efficacy and the healthcare professional will rate the practicality of study treatment at 30 min after randomisation using a 5-point Likert scale. Adverse events will be recorded until safety follow-up at 14 ± 2 days. Vital signs will be measured at baseline, 10 and 30 min. The primary aim is to demonstrate non-inferiority of methoxyflurane versus SoC for the change in VAS pain intensity from baseline (randomisation) to 3, 5 and 10 min.

Trial Registration

EudraCT number: 2017-001565-25. Clinicaltrials.gov identifier: NCT03585374.

Funding

Mundipharma Pharmaceuticals srl.

Electronic supplementary material

The online version of this article (10.1007/s12325-018-0830-x) contains supplementary material, which is available to authorized users.

Prospective, Multicentre Trial of Methoxyflurane for Acute Trauma-Related Pain in Helicopter Emergency Medical Systems and Hostile Environments: METEORA Protocol

Introduction

The inhalational analgesic low-dose methoxyflurane has been widely used by Australian ambulance services since 1975 and is now approved in Europe for emergency relief of moderate-to-severe trauma-related pain in conscious adult patients. The use of methoxyflurane in hostile environments is of special interest given its portability, ease of use and rapid onset of action. This trial will investigate the efficacy, tolerability and practicality of use of inhaled methoxyflurane in patients with moderate-to-severe trauma-related pain rescued from hostile mountainous environments by the Helicopter Emergency Medical Service (HEMS) in Italy.

Methods

METEORA is a phase IIIb, prospective, single-arm, multicentre trial. Approximately 200 adult patients with a pain score of at least 4 on the numerical rating scale (NRS) due to limb trauma rescued by HEMS will be enrolled. Patients will receive up to 2 × 3 mL methoxyflurane, self-administered by the patient by inhalation under medical supervision. Rescue medication will be permitted if required.

Planned Outcomes

Pain intensity will be measured using a 100-mm visual analogue scale (VAS) at baseline, at 5, 10, 15, 20, 30, 45 and 60 min after the start of methoxyflurane inhalation and when positioning the patient on a spinal board or stretcher; and also using the NRS at enrolment and at 10 min. Use of rescue medication (yes/no) will be recorded. The patient will rate efficacy and the healthcare professional will rate practicality of methoxyflurane treatment at 30 and 60 min using a 5-point Likert scale. Vital signs will be measured at baseline, 10, 30 and 60 min. Assessments after 30 min will only be performed for patients using a second inhaler. Adverse events will be recorded until safety follow-up at 3 ± 1 days. The primary endpoint is the percentage of patients achieving at least 30% improvement from baseline in VAS pain intensity within the first 10 min of methoxyflurane administration.

Trial Registration

EudraCT number: 2017-004601-40.

Funding

Mundipharma Pharmaceuticals, srl.

Plain Language Summary

Plain language summary available for this article.

Electronic supplementary material

The online version of this article (10.1007/s12325-018-0816-8) contains supplementary material, which is available to authorized users.

The treatment of pain is an essential part of the management of injured patients. In emergency rescue situations, rapid and effective pain relief can reduce the patient’s stress and discomfort, making it easier to assess, treat and extricate them. Currently available painkillers have limitations such as being slow to work (oral medications), requiring needles (intravenous medications) or prolonged monitoring and observation (e.g. opioids). An inhaled painkiller (methoxyflurane) is now available in Europe for emergency relief of moderate-to-severe pain in conscious adult patients with trauma (injury) and associated pain. Methoxyflurane is administered via a hand-held inhaler, which provides pain relief within 6–10 inhalations and lasts for 25–30 min, on average, when used continuously. The patient can control his/her own level of pain relief and a second inhaler may be used if required. Methoxyflurane has been widely used by Australian ambulance services since 1975 and its effectiveness and safety are well established. Considering its ease of use and rapid action, inhaled methoxyflurane may be useful in emergency situations in remote and hostile environments. A new trial (METEORA) will assess the use of methoxyflurane in 200 patients with limb injuries who are rescued from mountainous environments by the Helicopter Emergency Medical Service (HEMS) in Italy. Patients with moderate-to-severe pain will receive inhaled methoxyflurane under medical supervision. A second inhaler and/or additional pain-relieving medication will be provided if necessary. The trial will assess the reduction in pain intensity and whether additional pain-relieving medication is needed. The practicality of use of methoxyflurane in the emergency rescue situation and any side effects will also be evaluated.

The role of inhaled methoxyflurane in acute pain management

Methoxyflurane is an inhaled analgesic administered via a disposable inhaler which has been used in Australia for over 40 years for the management of pain associated with trauma and for medical procedures in children and adults. Now available in 16 countries worldwide, it is licensed in Europe for moderate to severe pain associated with trauma in conscious adults, although additional applications are being made to widen the range of approved indications. Considering these ongoing developments, we reviewed the available evidence on clinical usage and safety of inhaled analgesic methoxyflurane in trauma pain and in medical procedures in both adults and children. Published data on methoxyflurane in trauma and procedural pain show it to be effective, well tolerated, and highly rated by patients, providing rapid onset of analgesia. Methoxyflurane has a well-established safety profile; adverse events are usually brief and self-limiting, and no clinically significant effects on vital signs or consciousness levels have been reported. Nephrotoxicity previously associated with methoxyflurane at high anesthetic doses is not reported with low analgesic doses. Although two large retrospective comparative studies in the prehospital setting showed inhaled analgesic methoxyflurane to be less effective than intravenous morphine and intranasal fentanyl, this should be balanced against the administration, supervision times, and safety profile of these agents. Given the limitations of currently available analgesic agents in the prehospital and emergency department settings, the ease of use and portability of methoxyflurane combined with its rapid onset of effective pain relief and favorable safety profile make it a useful nonopioid option for pain management. Except for the STOP! study, which formed the basis for approval in trauma pain in Europe, and a few smaller randomized controlled trials (RCTs), much of the available data are observational or retrospective, and further RCTs are currently underway to provide more robust data.

Derivation of an occupational exposure limit for an inhalation analgesic methoxyflurane (Penthrox(®))

Methoxyflurane (MOF) a haloether, is an inhalation analgesic agent for emergency relief of pain by self administration in conscious patients with trauma and associated pain. It is administered under supervision of personnel trained in its use. As a consequence of supervised use, intermittent occupational exposure can occur. An occupational exposure limit has not been established for methoxyflurane. Human clinical and toxicity data have been reviewed and used to derive an occupational exposure limit (referred to as a maximum exposure level, MEL) according to modern principles. The data set for methoxyflurane is complex given its historical use as anaesthetic. Distinguishing clinical investigations of adverse health effects following high and prolonged exposure during anaesthesia to assess relatively low and intermittent exposure during occupational exposure requires an evidence based approach to the toxicity assessment and determination of a critical effect and point of departure. The principal target organs are the kidney and the central nervous system and there have been rare reports of hepatotoxicity, too. Methoxyflurane is not genotoxic based on in vitro bacterial mutation and in vivo micronucleus tests and it is not classifiable (IARC) as a carcinogenic hazard to humans. The critical effect chosen for development of a MEL is kidney toxicity. The point of departure (POD) was derived from the concentration response relationship for kidney toxicity using the benchmark dose method. A MEL of 15 ppm (expressed as an 8 h time weighted average (TWA)) was derived. The derived MEL is at least 50 times higher than the mean observed TWA (0.23 ppm) for ambulance workers and medical staff involved in supervising use of Penthrox. In typical treatment environments (ambulances and treatment rooms) that meet ventilation requirements the derived MEL is at least 10 times higher than the modelled TWA (1.5 ppm or less) and the estimated short term peak concentrations are within the MEL. The odour threshold for MOF of 0.13-0.19 ppm indicates that the odour is detectable well below the MEL. Given the above considerations the proposed MEL is health protective.