A randomised, double-blind, placebo-controlled study to assess the safety and efficacy of methoxyflurane for procedural pain of a bone marrow biopsy

Haemodynamic effects of methoxyflurane versus fentanyl and placebo in hypovolaemia: a randomised, double-blind crossover study in healthy volunteers

Background

Methoxyflurane is approved for relief of moderate to severe pain in conscious adult trauma patients: it may be self-administrated and is well suited for use in austere environments. Trauma patients may sustain injuries causing occult haemorrhage compromising haemodynamic stability, and it is therefore important to elucidate whether methoxyflurane may adversely affect the haemodynamic response to hypovolaemia.

Methods

In this randomised, double-blinded, placebo-controlled, three-period crossover study, inhaled methoxyflurane 3 ml, i.v. fentanyl 25 μg, and placebo were administered to 15 healthy volunteers exposed to experimental hypovolaemia in the lower body negative pressure model. The primary endpoint was the effect of treatment on changes in cardiac output, while secondary endpoints were changes in stroke volume and mean arterial pressure and time to haemodynamic decompensation during lower body negative pressure.

Results

There were no statistically significant effects of treatment on the changes in cardiac output, stroke volume, or mean arterial pressure during lower body negative pressure. The time to decompensation was longer for methoxyflurane compared with fentanyl (hazard ratio 1.9; 95% confidence interval 0.4-3.4; P=0.010), whereas there was no significant difference to placebo (hazard ratio -1.3; 95% confidence interval -2.8 to 0.23; P=0.117).

Conclusions

The present study does not indicate that methoxyflurane has significant adverse haemodynamic effects in conscious adults experiencing hypovolaemia.

Clinical trial registration

ClinicalTrials.gov (NCT04641949) and EudraCT (2019-004144-29) https://www.clinicaltrialsregister.eu/ctr-search/trial/2019-004144-29/NO.

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.

Determination of equi-analgesic doses of inhaled methoxyflurane versus intravenous fentanyl using the cold pressor test in volunteers: a randomised, double-blinded, placebo-controlled crossover study

Background

Inhaled methoxyflurane for acute pain relief has demonstrated an analgesic effect superior to placebo. Data comparing methoxyflurane to an opioid are needed. The aim of this study was to determine the equi-analgesic doses of inhaled methoxyflurane vs i.v. fentanyl. Both drugs have an onset within minutes and an analgesic effect of 20–30 min.

Methods

Twelve subjects were included in a randomised, double-blinded, placebo-controlled crossover study with four treatments: placebo (NaCl 0.9%), fentanyl 25 μg i.v., fentanyl 50 μg i.v., or inhaled methoxyflurane 3 ml. The subjects reported pain intensity using the verbal numeric rating scale (VNRS) from 0 to 10 during the cold pressor test (CPT). The CPT was performed before (CPT 1), 5 min (CPT 2), and 20 min (CPT 3) after drug administration.

Results

Inhaled methoxyflurane and fentanyl 25 μg reduced VNRS scores significantly compared with placebo at CPT 2 (–1.14 [estimated difference in VNRS between treatment groups with 95% confidence interval {CI}: –1.50 to –0.78]; –1.15 [95% CI: –1.51 to –0.79]; both P<0.001) and CPT 3 (–0.60 [95% CI: –0.96 to –0.24]; –0.84 [95% CI: –1.20 to –0.47]; both P<0.001). There were no significant differences between the two drugs. Methoxyflurane had significantly higher VNRS scores than fentanyl 50 μg at CPT 2 (0.90 [95% CI: 0.54–1.26]; P<0.001) and CPT 3 (0.57 [95% CI: 0.21–0.94]; P<0.001).

Conclusions

Inhaled methoxyflurane 3 ml was equi-analgesic to fentanyl 25 μg i.v. at CPT 2. Both resulted in significantly less pain than placebo. Fentanyl 50 μg i.v. demonstrated analgesia superior to methoxyflurane.

Clinical trial registration

NCT03894800

Management of Pain and Anxiety during Bone Marrow Aspiration: An Italian National Survey

BACKGROUND

Bone marrow aspiration (BMA) or biopsy is a necessary and frequent procedure for diagnosis and monitoring of hematological diseases. Pharmacological pain management approaches exist; however, previous experience and psychological preparation for BMA may impact pain perception.

AIMS

This study aimed to explore current practices in procedural pain management for BMA or biopsy.

DESIGN/SETTING/PARTICIPANTS

A cross-sectional internet-based survey was performed by the Nurses Group of the Italian Transplant Group (GITMO). Participants were nurses working in bone marrow transplant centers regularly performing BMA/biopsies.

RESULTS

Sixty out of 94 centers receiving the survey responded (63.8%), 47 adult and 13 pediatric centers. The majority of them (75%) provided only verbal information for patient preparation before BMA. . Injected local anesthetics were used in 55.4% of centers, and combined with topical anesthetics in 33.9% of centers. Use of oral anesthetics was rare; however, anxiolytics and benzodiazepines were occasionally used (18.3%, 18.3% respectively). All pediatric centers used deep sedation for the procedure (p < .001), but drug choice depended on anesthetist preference. Ice packs (35.0%) and oral analgesia as required (40.0%) were used for postprocedural pain. Nurses perceived their patients' pain scores as relatively low (3.5 on scale 0-10), but recognized that it was a painful procedure provoking anxiety, and that pain management could be improved.

CONCLUSIONS

Results revealed the lack of a standardized approach to procedural pain management for BMA in this study sample. Assessing a patient's pain experience is a key component to identifying effective pain management for BMA.

The use of methoxyflurane (Penthrox®) for procedural analgesia in the emergency department and pre-hospital environment

Background

Methoxyflurane is an inhaled analgesic agent licensed in the United Kingdom for the relief of moderate to severe pain in conscious patients with trauma. Methoxyflurane has been widely used by Australian ambulance services since the 1970s.

Aims

Primary aim: To assess the efficacy of methoxyflurane for procedural analgesia in the emergency department and pre-hospital environment. Secondary aims: to assess the efficacy of methoxyflurane for analgesia in the emergency department and pre-hospital environment; to assess the safety of methoxyflurane as an analgesic.

Method

A literature search of Medline, EMBASE, CINAHL and Cochrane databases was performed. A total of 59 articles were reviewed.

Results

One study using methoxyflurane for procedural analgesia in the emergency department was found. Multiple studies demonstrate the use of methoxyflurane for procedural analgesia for painful procedures outside the emergency department. Compared to other analgesics, methoxyflurane provides adequate analgesia. Overall, methoxyflurane is inferior to fentanyl or morphine, but it provides quicker onset analgesia compared to fentanyl and tramadol. It provides similar analgesia to nitrous oxide. Nephrotoxicity is dose dependent. Used in the analgesic doses, the risk of clinically significant kidney injury is negligible. Rare cases of unpredictable, severe hepatitis are reported.

Discussion

The efficacy of methoxyflurane and its acceptability to patients and clinicians has been shown in a number of studies. As would be expected in any procedural analgesic choice, patient and clinician factors and the procedure planned are all important considerations. Compared to other analgesic agents, methoxyflurane performs favourably with a low chance of adverse events.

Conclusion

Methoxyflurane is an efficacious analgesic agent in the emergency department and pre-hospital environment. It is easily portable and has a rapid onset. Methoxyflurane is suitable for use in procedural analgesia and as a bridging analgesic agent. Risks to the patient from renal or hepatic injury, cardiorespiratory depression or malignant hyperthermia are low.

The Reincarnation of Methoxyflurane

Methoxyflurane was an inhaled agent commonly used for general anesthesia in the 1960s, but its clinical role gradually decreased in the 1970s because of reports of dose-dependent nephrotoxicity. In 1999 its manufacturer, Abbott Laboratories, discontinued distribution of methoxyflurane in the United States and Canada. Outside of North America, however, methoxyflurane has been reborn as an inhaled analgesic used for pain relief in the prehospital setting and for minor surgical procedures. First used in Australia and New Zealand, and subsequently in over thirty-seven other countries, low concentrations of methoxyflurane are administered with a hand-held inhaler which provides conscious sedation, so that patients can self-assess their level of pain and control the amount of inhaled agent. The Penthrox inhaler, originally developed in Australia after several other hand-held vaporizers were tried, is currently being used worldwide as a portable and disposable self-administered agent delivery system. Methoxyflurane-induced nephrotoxicity continues to be a major concern, but with cautious administration of recommended doses methoxyflurane has been established as a remarkably safe analgesic agent with minimal side effects for patients in need of rapid and potent pain relief.

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.

A review of the safety and efficacy of inhaled methoxyflurane as an analgesic for outpatient procedures

Methoxyflurane delivered via a hand-held inhaler is a proven analgesic which has been used in Australasia for emergency relief of trauma associated pain since the 1970s. The agent is self-administered by the patient under the supervision of trained personnel. More than 5 million patients have received inhaled methoxyflurane without significant side effects. Methoxyflurane is also licensed in Australasia for the relief of pain in monitored conscious patients requiring analgesia for minor surgical procedures. Recent clinical studies undertaken in a variety of outpatient settings, including colonoscopy, prostate biopsy, dental procedures, bone marrow biopsy, and the management of burns dressings, indicate that inhaled methoxyflurane has significant analgesic activity, without producing deep sedation or respiratory depression. Return to full psychomotor activity is rapid. Thus, methoxyflurane may be a suitable and well-tolerated alternative to traditional i.v. sedative agents for outpatient medical and surgical procedures. There are direct advantages to the patient in terms of rapid recovery and an early return to normal activities, and significant benefits for outpatient departments in terms of cost saving and rate of throughput. Further randomised controlled trials comparing the efficacy, safety, and cost-effectiveness of inhaled methoxyflurane against traditional i.v. sedative techniques are currently in progress.

Psychomotor and cognitive effects of 15-minute inhalation of methoxyflurane in healthy volunteers: implication for post-colonoscopy care

Background and study aims: Colonoscopy with portal inhaled methoxyflurane (Penthrox) is highly feasible with low sedation risk and allows earlier discharge. It is unclear if subjects can return to highly skilled psychomotor skill task shortly after Penthrox assisted colonoscopy. We evaluated the psychomotor and cognitive effects of 15-minute inhalation of Penthrox in adults. Patients and methods: Sixty healthy volunteers (18 to 80 years) were studied on 2 occasions with either Penthrox or placebo in a randomized, double-blind fashion. On each occasion, the subject's psychomotor function was examined before, immediately, 30, 60, 120, 180 and 240 min after a 15-minute inhalation of studied drug, using validated psychomotor tests (Digit Symbol Substitution Test (DSST), auditory reaction time (ART), eye-hand coordination (EHC) test, trail making test (TMT) and logical reasoning test (LRT). Results: Compared to placebo, a 15-minute Penthrox inhalation led to an immediate but small impairment of DSST (P < 0.001), ART (P < 0.001), EHC (P < 0.01), TMT (P = 0.02) and LRT (P = 0.04). In all subjects, the performance of all 5 tests normalized by 30 minutes after inhalation, and was comparable to that with placebo. Although increasing age was associated with a small deterioration in psychomotor testing performance, the magnitude of Penthrox effects remained comparable among all age groups. Conclusions: In all age groups, a 15-minute Penthrox inhalation induces acute but short-lasting impairment of psychomotor and cognitive performance, which returns to normal within 30 minutes , indicating that subjects who have colonoscopy with Penthrox can return to highly skilled psychomotor skills tasks such as driving and daily work the same day.

Methoxyflurane Analgesia in Adult Patients in the Emergency Department: A Subgroup Analysis of a Randomized, Double-blind, Placebo-controlled Study (STOP!)

INTRODUCTION

Acute pain remains highly prevalent in the Emergency Department (ED) setting. This double-blind, randomized, placebo-controlled UK study investigated the efficacy and safety of low-dose methoxyflurane analgesia for the treatment of acute pain in the ED in the adult population of the STOP! trial.

METHODS

Patients presenting to the ED requiring analgesia for acute pain (pain score of 4-7 on the Numerical Rating Scale) due to minor trauma were randomized in a 1:1 ratio to receive methoxyflurane (up to 6 mL) or placebo (normal saline), both via a Penthrox® (Medical Developments International Limited, Scoresby, Australia) inhaler. Rescue medication (paracetamol/opioids) was available immediately upon request. Change from baseline in visual analog scale (VAS) pain intensity was the primary endpoint.

RESULTS

300 adult and adolescent patients were randomized; data are presented for the adult subgroup (N = 204). Mean baseline VAS pain score was ~66 mm in both groups. The mean change from baseline to 5, 10, 15 and 20 min was greater for methoxyflurane (-20.7, -27.4, -33.3 and -34.8 mm, respectively) than placebo (-8.0, -11.1, -12.3 and -15.2 mm, respectively). The primary analysis showed a highly significant treatment effect overall across all four time points (-17.4 mm; 95% confidence interval: -22.3 to -12.5 mm; p < 0.0001). Median time to first pain relief was 5 min with methoxyflurane [versus 20 min with placebo; (hazard ratio: 2.32; 95% CI: 1.63, 3.30; p < 0.0001)]; 79.4% of methoxyflurane-treated patients experienced pain relief within 1-10 inhalations. 22.8% of placebo-treated patients requested rescue medication within 20 min compared with 2.0% of methoxyflurane-treated patients (p = 0.0003). Methoxyflurane treatment was rated 'Excellent', 'Very Good' or 'Good' by 77.6% of patients, 74.5% of physicians and 72.5% of nurses. Treatment-related adverse events (mostly dizziness/headache) were reported by 42.2% of patients receiving methoxyflurane and 14.9% of patients receiving placebo; none caused withdrawal and the majority were mild and transient.

CONCLUSION

The results of this study support the evidence from previous trials that low-dose methoxyflurane administered via the Penthrox inhaler is a well-tolerated, efficacious and rapid-acting analgesic.

FUNDING

Medical Developments International (MDI) Limited and Mundipharma Research GmbH & Co.KG.

TRIAL REGISTRATION

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

Self-administered methoxyflurane for procedural analgesia: experience in a tertiary Australasian centre

Methoxyflurane, an agent formerly used as a volatile anaesthetic but that has strong analgesic properties, will soon become available again in the UK and Europe in the form of a small hand-held inhaler. We describe our experience in the use of inhaled methoxyflurane for procedural analgesia within a large tertiary hospital. In a small pilot crossover study of patients undergoing burns-dressing procedures, self-administered methoxyflurane inhalation was preferred to ketamine-midazolam patient-controlled analgesia by five of eight patients. Patient and proceduralist outcomes and satisfaction were recorded from a subsequent case series of 173 minor surgical and radiological procedures in 123 patients performed using inhaled methoxyflurane. The procedures included change of dressing, minor debridement, colonoscopy and incision-and-drainage of abscess. There was a 97% success rate of methoxyflurane analgesia to facilitate these procedures. Limitations of methoxyflurane include maximal daily and weekly doses, and uncertainty regarding its safety in patients with pre-existing renal disease.

Efficacy of the methoxyflurane as bridging analgesia during epidural placement in laboring parturient

Background:

Establishing an epidural in an agitated laboring woman can be challenging. The ideal pain control technique in such a situation should be effective, fast acting, and short lived. We assessed the efficacy of inhalational methoxyflurane (Penthrox™) analgesia as bridging analgesia for epidural placement.

Materials and Methods:

Sixty-four laboring women who requested epidural analgesia with pain score of ≥7 enrolled in an observational study, 56 of which completed the study. The parturients were instructed to use the device prior to the onset of uterine contraction pain and to stop at the peak of uterine contraction, repeatedly until epidural has been successfully placed. After each (methoxyflurane inhalation-uterine contraction) cycle, pain, Richmond Agitation Sedation Scale (RASS), nausea and vomiting were evaluated. Maternal and fetal hemodynamics and parturient satisfaction were recorded.

Results:

The mean baseline pain score was 8.2 ± 1.5 which was reduced to 6.2 ± 2.0 after the first inhalation with a mean difference of 2.0 ± 1.1 (95% confidence interval 1.7-2.3, P < 0.0001), and continued to decrease significantly over the study period (P < 0.0001). The RASS scores continuously improved after each cycle (P < 0.0001). Only 1 parturient from the cohort became lightly sedated (RASS = −1). Two parturients vomited, and no significant changes in maternal hemodynamics or fetal heart rate changes were identified during treatment. 67% of the parturients reported very good or excellent satisfaction with treatment.

Conclusion:

Penthrox™ provides rapid, robust, and satisfactory therapy to control pain and restlessness during epidural placement in laboring parturient.

A phase II study on the efficacy and safety of procedural analgesia with fentanyl buccal tablet in cancer patients for the placement of indwelling central venous access systems

Background

Pain in cancer patients is often related to oncologic therapies and diagnostic procedures. The placement of fully implantable venous access systems is a very common procedure in oncology patients. Local anaesthesia is the method most commonly used to overcome pain related to this surgical procedure, but the local anaesthetic may be unable to completely eradicate all pain. This study investigates the effectiveness and safety of fentanyl buccal tablet (FBT), administered by OraVescent® technology, in reducing procedural pain related to the placement of indwelling central venous access systems (Ports) in opioid-naïve cancer patients.

Methods

Inpatients who required an indwelling vascular access (Port) were preoperatively assessed with a self-assessment questionnaire on anxiety and pain. A 100 μg FBT was administered 10 min before preparation of the operating field. A self-assessment scale for pain experienced during the procedure was administered at the end of the procedure. Vital signs and the presence of any side effects or bothersome symptoms were monitored during the procedure, at the end, and 4 h later.

Results

From October 2012 to June 2014, 65 patients were enrolled in the study. A total of 61 (93.9 %) patients perceived no or a little pain during the procedure. Four patients (6.2 %) reported a lot of pain. No patient reported very severe pain. This data is significant in terms of the lower than expected presence of pain (Fisher test p = 0.0018) as assessed in our previous experience without procedural analgesia. The most common side effects of FBT was drowsiness, experienced by 28 patients at the end of the procedure (43.1 %), significantly reduced (p < 0.01) to 8 patients after 4 h (12.5 %). Nausea was present in 6 cases at the end of the procedure (9.2 %) and in 7 cases 4 h later (10.9 %). Vomiting was present in 3 cases at the end (4.7 %) and in 2 other patients after 4 h (7.8 %). No significant change of vital parameters was observed between the baseline and the subsequent measurements in all patients studied.

Conclusions

The significant improvement in the number of patients experiencing little or no pain, accompanied by a lower number of non-severe side effects, suggests that FBT is a valid, practical and safe method of procedural analgesia. It will be necessary to perform further studies, taking into account the need for standard antiemetic pre-medication to minimise the incidence of nausea and vomiting.

Analgesic use of inhaled methoxyflurane: Evaluation of its potential nephrotoxicity

Methoxyflurane is a volatile, halogenated analgesic, self-administered in a controlled low dose from the Penthrox(®) inhaler for short-term pain relief. It was formerly used in significantly higher doses to produce anaesthesia, when it caused a specific type of dose-related renal tubular damage. The pathogenesis of the renal damage and clinical use of methoxyflurane are discussed here with evidence that a low but effective analgesic dose is not associated with the risk of renal adverse effects. The maximum dose employed to produce analgesia is limited to methoxyflurane 6 mL/day and 15 mL/week, producing a minimum alveolar concentration (MAC) of 0.59 MAC-hours. Renal damage is due to the metabolism of methoxyflurane and release of fluoride ions. Exposure of humans to methoxyflurane ≤2.0 MAC-hours, resulting in serum fluoride ≤40 µmol/L, has not been associated with renal tubular toxicity. The safety margin of analgesic use of methoxyflurane in the Penthrox ((®)) inhaler is at least 2.7- to 8-fold, based on methoxyflurane MAC-hours or serum fluoride level, with clinical experience suggesting it is higher. It is concluded from clinical experience in emergency medicine, surgical procedures and various experimental and laboratory investigations that the analgesic use of methoxyflurane in subanaesthetic doses in the Penthrox inhaler does not carry a risk of nephrotoxicity.

Penthrox alone versus Penthrox plus periprostatic infiltration of local analgesia for analgesia in transrectal ultrasound-guided prostate biopsy

BACKGROUND

The objective of this study was to compare pain intensity in patients undergoing transrectal ultrasound (TRUS)-guided biopsy of the prostate with Penthrox alone compared with Penthrox plus periprostatic infiltration of local analgesia (PILA).

METHOD

Seventy-two subjects participated in this study after receiving appropriate education. Forty-two patients self-administered inhaled Penthrox (3 mL methoxyflurane) alone for analgesia (Group A), followed by 30 patients who self-administered Penthrox and received PILA with 5 mL of 2% lignocaine. All subjects had TRUS biopsy performed. Immediately after the procedure, patients were asked to rate their pain intensity using a numerical verbal rating scale from 0 to 10.

RESULTS

Baseline characteristics of the two groups were similar. Patients in Group B reported significantly lower post TRUS biopsy median pain intensity of 2 (1-3) compared with Group A subjects who reported a median post TRUS biopsy pain intensity of 3 (2-5) (P = 0.014). A total of 72 men underwent TRUS-guided biopsy. All patients indicated they would be happy to have another TRUS-guided prostate biopsy in the future.

CONCLUSION

Our study shows that Penthrox plus PILA shows promise as an efficacious and easily tolerated analgesic technique for outpatient TRUS biopsy, keeping resource use to a minimum. Planning for a multi-centre, double-blind randomized control trial comparing Penthrox plus PILA with PILA alone is presently underway.

STOP!: a randomised, double-blind, placebo-controlled study of the efficacy and safety of methoxyflurane for the treatment of acute pain

Objective

To evaluate the short-term efficacy and safety of methoxyflurane for the treatment of acute pain in patients presenting to an emergency department (ED) with minor trauma.

Methods

STOP! was a randomised, double-blind, multicentre, placebo-controlled study conducted at six sites in the UK. A total of 300 patients, 90 of whom were adolescent patients (age 12–17 years), were randomised 150:150 to receive either methoxyflurane via a Penthrox inhaler or placebo. The primary end point of the study was the change in pain intensity as measured using the visual analogue scale (VAS) from baseline to 5, 10, 15 and 20 min after the start of study drug inhalation. Patients were supplied with one inhaler containing 3 mL methoxyflurane or 5 mL placebo after enrolment and initial assessments. Age group (adolescent/adult) and baseline VAS score were controlled for in the statistical analyses.

Results

A total of 149 patients received methoxyflurane, and 149 patients received placebo. Demographic and baseline characteristics were comparable between the groups. Methoxyflurane reduced pain severity significantly more than placebo (p<0.0001) at all time points tested, with the greatest estimated treatment effect of −18.5 mm (adjusted change from baseline) seen at 15 min after the start of treatment. Methoxyflurane was well tolerated, with the majority of adverse reactions being mild, transient and in line with anticipated pharmacological action.

Conclusion

The results of this study suggest that methoxyflurane administered via the Penthrox inhaler is an efficacious, safe, and rapidly acting analgesic.

Trial registration number:

NCT01420159.