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‘Green Whistle’ Provides Pain Relief -- But Not in the US
This discussion was recorded on March 29, 2024. The transcript has been edited for clarity.
Robert D. Glatter, MD: Joining me today to discuss the use of methoxyflurane (Penthrox), an inhaled nonopioid analgesic for the relief of acute pain, is Dr. William Kenneth (Ken) Milne, an emergency physician at Strathroy Middlesex General Hospital in Ontario, Canada, and the founder of the well-known podcast The Skeptics’ Guide to Emergency Medicine (SGEM).
Also joining me is Dr. Sergey Motov, an emergency physician and research director at Maimonides Medical Center in Brooklyn, New York, and an expert in pain management. I want to welcome both of you and thank you for joining me.
RAMPED Trial: Evaluating the Efficacy of Methoxyflurane
Dr. Glatter: Ken, your recent post on Twitter [now X] regarding the utility of Penthrox in the RAMPED trial really caught my attention. While the trial was from 2021, it really is relevant regarding the prehospital management of pain in the practice of emergency medicine, and certainly in-hospital practice. I was hoping you could review the study design but also get into the rationale behind the use of this novel agent.
William Kenneth (Ken) Milne, MD, MSc: Sure. I’d be happy to kick this episode off with talking about a study that was published in 2020 in Academic Emergency Medicine. It was an Australian study by Brichko et al., and they were doing a randomized controlled trial looking at methoxyflurane vs standard care.
They selected out a population of adults, which they defined as 18-75 years of age. They were in the prehospital setting and they had a pain score of greater than 8. They gave the participants methoxyflurane, which is also called the “green whistle.” They had the subjects take that for their prehospital pain, and they compared that with whatever your standard analgesic in the prehospital setting would be.
Their primary outcome was how many patients had at least 50% reduction in their pain score within 30 minutes. They recruited about 120 people, and they found that there was no statistical difference in the primary outcome between methoxyflurane and standard care. Again, that primary outcome was a reduction in pain score by greater than 50% at 30 minutes, and there wasn’t a statistical difference between the two.
There are obviously limits to any study, and it was a convenience sample. This was an unmasked trial, so people knew if they were getting this green whistle, which is popular in Australia. People would be familiar with this device, and they didn’t compare it with a sham or placebo group.
Pharmacology of Penthrox: Its Role and Mechanism of Action
Dr. Glatter: The primary outcome wasn’t met, but certainly secondary outcomes were. There was, again, a relatively small number of patients in this trial. That said, there was significant pain relief. I think there are issues with the trial, as with any trial limitations.
Getting to the pharmacology of Penthrox, can you describe this inhaled anesthetic and how we use it, specifically its role at the subanesthetic doses?
Sergey M. Motov, MD: Methoxyflurane is embedded in the green whistle package, and that whole contraption is called Penthrox. It’s an inhaled volatile fluorinated hydrocarbon anesthetic that was predominantly used, I’d say 40, 50 years ago, for general anesthesia and slowly but surely fell out of favor due to the fact that, when used for prolonged duration or in supratherapeutic doses, there were cases of severe or even fatal nephrotoxicity and hepatotoxicity.
In the late ‘70s and early ‘80s, all the fluranes came on board that are slightly different as general anesthetics, and methoxyflurane started slowly falling out of favor. Because of this paucity and then a subsequent slightly greater number of cases of nephrotoxicity and hepatotoxicity, [the US Food and Drug Administration] FDA made a decision to pull the drug off the market in 2005. FDA successfully accomplished its mission and since then has pretty much banned the use of inhaled methoxyflurane in any shape, form, or color in the United States.
Going back to the green whistle, it has been used in Australia probably for about 50-60 years, and has been used in Europe for probably 10-20 years. Ken can attest that it has been used in Canada for at least a decade and the track record is phenomenal.
We are using subanesthetic, even supratherapeutic doses that, based on available literature, has no incidence of this fatal hepatotoxicity or nephrotoxicity. We’re talking about 10 million doses administered worldwide, except in the United States. There are 40-plus randomized clinical trials with over 30,000 patients enrolled that prove efficacy and safety.
That’s where we are right now, in a conundrum. We have a great deal of data all over the world, except in the United States, that push for the use of this noninvasive, patient-controlled nonopioid inhaled anesthetic. We just don’t have the access in North America, with the exception of Canada.
Regulatory Hurdles: Challenges in FDA Approval
Dr. Glatter: Absolutely. The FDA wants to be cautious, but if you look at the evidence base of data on this, it really indicates otherwise. Do you think that these roadblocks can be somehow overcome?
Dr. Milne: In the 2000s and 2010s, everybody was focused on opioids and all the dangers and potential adverse events. Opioids are great drugs like many other drugs; it depends on dose and duration. If used properly, it’s an excellent drug. Well, here’s another excellent drug if it’s used properly, and the adverse events are dependent on their dose and duration. Penthrox, or methoxyflurane, is a subtherapeutic, small dose and there have been no reported cases of addiction or abuse related to these inhalers.
Dr. Glatter: That argues for the point — and I’ll turn this over to you, Sergey — of how can this not, in my mind, be an issue that the FDA can overcome.
Dr. Motov: I agree with you. It’s very hard for me to speak on behalf of the FDA, to allude to their thinking processes, but we need to be up to speed with the evidence. The first thing is, why don’t you study the drug in the United States? I’m not asking you to lift the ban, which you put in 2005, but why don’t you honor what has been done over two decades and at least open the door a little bit and let us do what we do best? Why don’t you allow us to do the research in a controlled setting with a carefully, properly selected group of patients without underlying renal or hepatic insufficiency and see where we’re at?
Let’s compare it against placebo. If that’s not ethical, let’s compare it against active comparators — God knows we have 15-20 drugs we can use — and let’s see where we’re at. Ken has been nothing short of superb when it comes to evidence. Let us put the evidence together.
Dr. Milne: If there were concerns decades ago, those need to be addressed. As science is iterative and as other information becomes available, the scientific method would say, Let’s reexamine this and let’s reexamine our position, and do that with evidence. To do that, it has to have validity within the US system. Someone like you doing the research, you are a pain research guru; you should be doing this research to say, “Does it work or not? Does this nonapproval still stand today in 2024?”
Dr. Motov: Thank you for the shout-out, and I agree with you. All of us, those who are interested, on the frontiers of emergency care — as present clinicians — we should be doing this. There is nothing that will convince the FDA more than properly and rightly conducted research, time to reassess the evidence, and time to be less rigid. I understand that you placed a ban 20 years ago, but let’s go with the science. We cannot be behind it.
Exploring the Ecological Footprint of Methoxyflurane
Dr. Milne: There was an Austrian study in 2022 and a very interesting study out of the UK looking at life-cycle impact assessment on the environment. If we’re not just concerned about patient care —obviously, we want to provide patients with a safe and effective product, compared with other products that are available that might not have as good a safety profile — this looks at the impact on the environment.
Dr. Glatter: Ken, can you tell me about some of your recent research regarding the environmental effects related to use of Penthrox, but also its utility pharmacologically and its mechanism of action?
Dr. Milne: There was a really interesting study published this year by Martindale in the Emergency Medicine Journal. It took a different approach to this question about could we be using this drug, and why should we be using this drug? Sergey and I have already talked about the potential benefits and the potential harms. I mentioned opioids and some of the concerns about that. For this drug, if we’re using it in the prehospital setting in this little green whistle, the potential benefits look really good, and we haven’t seen any of the potential harms come through in the literature.
This was another line of evidence of why this might be a good drug, because of the environmental impact of this low-dose methoxyflurane. They compared it with nitrous oxide and said, “Well, what about the life-cycle impact on the environment of using this and the overall cradle-to-grave environmental impacts?”
Obviously, Sergey and I are interested in patient care, and we treat patients one at a time. But we have a larger responsibility to social determinants of health, like our environment. If you look at the overall cradle-to-grave environmental impact of this drug, it was better than for nitrous oxide when looking specifically at climate-change impact. That might be another reason, another line of argument, that could be put forward in the United States to say, “We want to have a healthy environment and a healthy option for patients.”
I’ll let Sergey speak to mechanisms of action and those types of things.
Dr. Motov: As a general anesthetic and hydrocarbonated volatile ones, I’m just going to say that it causes this generalized diffuse cortical depression, and there are no particular channels, receptors, or enzymes we need to worry much about. In short, it’s an inhaled gas used to put patients or people to sleep.
Over the past 30 or 40 years — and I’ll go back to the past decade — there have been numerous studies in different countries (outside of the United States, of course), and with the recent study that Ken just cited, there were comparisons for managing predominantly acute traumatic injuries in pediatric and adult populations presenting to EDs in various regions of the world that compared Penthrox, or the green whistle, with either placebo or active comparators, which included parenteral opioids, oral opioids, and NSAIDs.
The recent systematic review by Fabbri, out of Italy, showed that for ultra–short-term pain — we’re talking about 5, 10, or 15 minutes — inhaled methoxyflurane was found to be equal or even superior to standard of care, primarily related to parenteral opioids, and safety was off the hook. Interestingly, with respect to analgesia, they found that geriatric patients seemed to be responding more, with respect to changing pain score, than younger adults — we’re talking about ages 18-64 vs 65 or older. Again, we need to make sure that we carefully select those elderly people without underlying renal or hepatic insufficiency.
To wrap this up, there is evidence clearly supporting its analgesic efficacy and safety, even in comparison to commonly used and traditionally accepted analgesic modalities that we use for managing acute pain.
US Military Use and Implications for Civilian Practice
Dr. Glatter: Do you think that methoxyflurane’s use in the military will help propel its use in clinical settings in the US, and possibly convince the FDA to look at this closer? The military is currently using it in deployed combat veterans in an ongoing fashion.
Dr. Motov: I’m excited that the Department of Defense in the United States has taken the lead, and they’re being very progressive. There are data that we’ve adapted to the civilian environment by use of intranasal opioids and intranasal ketamine with more doctors who came out of the military. In the military, it’s a kingdom within a kingdom. I don’t know their relationship with the FDA, but I support the military’s pharmacologic initiative by honoring and disseminating their research once it becomes available.
For us nonmilitary folks, we still need to work with the FDA. We need to convince the FDA to let us study the drug, and then we need to pile the evidence within the United States so that the FDA will start looking at this favorably. It wouldn’t hurt and it wouldn’t harm. Any piece of evidence will add to the existing body of literature that we need to allow this medication to be available to us.
Safety Considerations and Aerosolization Concerns
Dr. Glatter: Its safety in children is well established in Australia and throughout the world. I think it deserves a careful look, and the evidence that you’ve both presented argues for the use of this prehospital but also in hospital. I guess there was concern in the hospital with underventilation and healthcare workers being exposed to the fumes, and then getting headaches, dizziness, and so forth. I don’t know if that’s borne out, Ken, in any of your experience in Canada at all.
Dr. Milne: We currently don’t have it in our shop. It’s being used in British Columbia right now in the prehospital setting, and I’m not aware of anybody using it in their department. It’s used prehospital as far as I know.
Dr. Motov: I can attest to it, if I may, because I had familiarized myself with the device. I actually was able to hold it in my hands. I have not used it yet but I had the prototype. The way it’s set up, there is an activated charcoal chamber that sits right on top of the device, which serves as the scavenger for exhaled air that contains particles of methoxyflurane. In theory, but I’m telling how it is in practicality, it significantly reduces occupational exposure, based on data that lacks specifics.
Although most of the researchers did not measure the concentration of methoxyflurane in ambient air within the treatment room in the EDs, I believe the additional data sources clearly stating that it’s within or even below the detectable level that would cause any harm. Once again, we need to honor pathology. We need to make sure that pregnant women will not be exposed to it.
Dr. Milne: In 2024, we also need to be concerned about aerosolizing procedures and aerosolizing treatments, and just take that into account because we should be considering all the potential benefits and all the potential harms. Going through the COVID-19 pandemic, there was concern about transmission and whether or not it was droplet or aerosolized.
There was an observational study published in 2022 in Austria by Trimmel in BMC Emergency Medicine showing similar results. It seemed to work well and potential harms didn’t get picked up. They had to stop the study early because of COVID-19.
We need to always focus in on the potential benefits, the potential harms; where does the science land? Where do the data lie? Then we move forward from that and make informed decisions.
Final Thoughts
Dr. Glatter: Are there any key takeaways you’d like to share with our audience?
Dr. Milne: One of the takeaways from this whole conversation is that science is iterative and science changes. When new evidence becomes available, and we’ve seen it accumulate around the world, we as scientists, as a researcher, as somebody committed to great patient care should revisit our positions on this. Since there is a prohibition against this medication, I think it’s time to reassess that stance and move forward to see if it still is accurate today.
Dr. Motov: I wholeheartedly agree with this. Thank you, Ken, for bringing this up. Good point.
Dr. Glatter: This has been a really informative discussion. I think our audience will certainly embrace this. Thank you very much for your time; it’s much appreciated.
Dr. Glatter is an assistant professor of emergency medicine at Zucker School of Medicine at Hofstra/Northwell in Hempstead, New York. He is a medical adviser for Medscape and hosts the Hot Topics in EM series. Dr. Milne is an emergency physician at Strathroy Middlesex General Hospital in Ontario, Canada, and the founder of the well-known podcast The Skeptics’ Guide to Emergency Medicine (SGEM). Dr. Motov is professor of emergency medicine and director of research in the Department of Emergency Medicine at Maimonides Medical Center in Brooklyn, New York. He is passionate about safe and effective pain management in the emergency department, and has numerous publications on the subject of opioid alternatives in pain management. Dr. Glatter, Dr. Milne, and Dr. Motov had no conflicts of interest to disclose.
A version of this article appeared on Medscape.com.
This discussion was recorded on March 29, 2024. The transcript has been edited for clarity.
Robert D. Glatter, MD: Joining me today to discuss the use of methoxyflurane (Penthrox), an inhaled nonopioid analgesic for the relief of acute pain, is Dr. William Kenneth (Ken) Milne, an emergency physician at Strathroy Middlesex General Hospital in Ontario, Canada, and the founder of the well-known podcast The Skeptics’ Guide to Emergency Medicine (SGEM).
Also joining me is Dr. Sergey Motov, an emergency physician and research director at Maimonides Medical Center in Brooklyn, New York, and an expert in pain management. I want to welcome both of you and thank you for joining me.
RAMPED Trial: Evaluating the Efficacy of Methoxyflurane
Dr. Glatter: Ken, your recent post on Twitter [now X] regarding the utility of Penthrox in the RAMPED trial really caught my attention. While the trial was from 2021, it really is relevant regarding the prehospital management of pain in the practice of emergency medicine, and certainly in-hospital practice. I was hoping you could review the study design but also get into the rationale behind the use of this novel agent.
William Kenneth (Ken) Milne, MD, MSc: Sure. I’d be happy to kick this episode off with talking about a study that was published in 2020 in Academic Emergency Medicine. It was an Australian study by Brichko et al., and they were doing a randomized controlled trial looking at methoxyflurane vs standard care.
They selected out a population of adults, which they defined as 18-75 years of age. They were in the prehospital setting and they had a pain score of greater than 8. They gave the participants methoxyflurane, which is also called the “green whistle.” They had the subjects take that for their prehospital pain, and they compared that with whatever your standard analgesic in the prehospital setting would be.
Their primary outcome was how many patients had at least 50% reduction in their pain score within 30 minutes. They recruited about 120 people, and they found that there was no statistical difference in the primary outcome between methoxyflurane and standard care. Again, that primary outcome was a reduction in pain score by greater than 50% at 30 minutes, and there wasn’t a statistical difference between the two.
There are obviously limits to any study, and it was a convenience sample. This was an unmasked trial, so people knew if they were getting this green whistle, which is popular in Australia. People would be familiar with this device, and they didn’t compare it with a sham or placebo group.
Pharmacology of Penthrox: Its Role and Mechanism of Action
Dr. Glatter: The primary outcome wasn’t met, but certainly secondary outcomes were. There was, again, a relatively small number of patients in this trial. That said, there was significant pain relief. I think there are issues with the trial, as with any trial limitations.
Getting to the pharmacology of Penthrox, can you describe this inhaled anesthetic and how we use it, specifically its role at the subanesthetic doses?
Sergey M. Motov, MD: Methoxyflurane is embedded in the green whistle package, and that whole contraption is called Penthrox. It’s an inhaled volatile fluorinated hydrocarbon anesthetic that was predominantly used, I’d say 40, 50 years ago, for general anesthesia and slowly but surely fell out of favor due to the fact that, when used for prolonged duration or in supratherapeutic doses, there were cases of severe or even fatal nephrotoxicity and hepatotoxicity.
In the late ‘70s and early ‘80s, all the fluranes came on board that are slightly different as general anesthetics, and methoxyflurane started slowly falling out of favor. Because of this paucity and then a subsequent slightly greater number of cases of nephrotoxicity and hepatotoxicity, [the US Food and Drug Administration] FDA made a decision to pull the drug off the market in 2005. FDA successfully accomplished its mission and since then has pretty much banned the use of inhaled methoxyflurane in any shape, form, or color in the United States.
Going back to the green whistle, it has been used in Australia probably for about 50-60 years, and has been used in Europe for probably 10-20 years. Ken can attest that it has been used in Canada for at least a decade and the track record is phenomenal.
We are using subanesthetic, even supratherapeutic doses that, based on available literature, has no incidence of this fatal hepatotoxicity or nephrotoxicity. We’re talking about 10 million doses administered worldwide, except in the United States. There are 40-plus randomized clinical trials with over 30,000 patients enrolled that prove efficacy and safety.
That’s where we are right now, in a conundrum. We have a great deal of data all over the world, except in the United States, that push for the use of this noninvasive, patient-controlled nonopioid inhaled anesthetic. We just don’t have the access in North America, with the exception of Canada.
Regulatory Hurdles: Challenges in FDA Approval
Dr. Glatter: Absolutely. The FDA wants to be cautious, but if you look at the evidence base of data on this, it really indicates otherwise. Do you think that these roadblocks can be somehow overcome?
Dr. Milne: In the 2000s and 2010s, everybody was focused on opioids and all the dangers and potential adverse events. Opioids are great drugs like many other drugs; it depends on dose and duration. If used properly, it’s an excellent drug. Well, here’s another excellent drug if it’s used properly, and the adverse events are dependent on their dose and duration. Penthrox, or methoxyflurane, is a subtherapeutic, small dose and there have been no reported cases of addiction or abuse related to these inhalers.
Dr. Glatter: That argues for the point — and I’ll turn this over to you, Sergey — of how can this not, in my mind, be an issue that the FDA can overcome.
Dr. Motov: I agree with you. It’s very hard for me to speak on behalf of the FDA, to allude to their thinking processes, but we need to be up to speed with the evidence. The first thing is, why don’t you study the drug in the United States? I’m not asking you to lift the ban, which you put in 2005, but why don’t you honor what has been done over two decades and at least open the door a little bit and let us do what we do best? Why don’t you allow us to do the research in a controlled setting with a carefully, properly selected group of patients without underlying renal or hepatic insufficiency and see where we’re at?
Let’s compare it against placebo. If that’s not ethical, let’s compare it against active comparators — God knows we have 15-20 drugs we can use — and let’s see where we’re at. Ken has been nothing short of superb when it comes to evidence. Let us put the evidence together.
Dr. Milne: If there were concerns decades ago, those need to be addressed. As science is iterative and as other information becomes available, the scientific method would say, Let’s reexamine this and let’s reexamine our position, and do that with evidence. To do that, it has to have validity within the US system. Someone like you doing the research, you are a pain research guru; you should be doing this research to say, “Does it work or not? Does this nonapproval still stand today in 2024?”
Dr. Motov: Thank you for the shout-out, and I agree with you. All of us, those who are interested, on the frontiers of emergency care — as present clinicians — we should be doing this. There is nothing that will convince the FDA more than properly and rightly conducted research, time to reassess the evidence, and time to be less rigid. I understand that you placed a ban 20 years ago, but let’s go with the science. We cannot be behind it.
Exploring the Ecological Footprint of Methoxyflurane
Dr. Milne: There was an Austrian study in 2022 and a very interesting study out of the UK looking at life-cycle impact assessment on the environment. If we’re not just concerned about patient care —obviously, we want to provide patients with a safe and effective product, compared with other products that are available that might not have as good a safety profile — this looks at the impact on the environment.
Dr. Glatter: Ken, can you tell me about some of your recent research regarding the environmental effects related to use of Penthrox, but also its utility pharmacologically and its mechanism of action?
Dr. Milne: There was a really interesting study published this year by Martindale in the Emergency Medicine Journal. It took a different approach to this question about could we be using this drug, and why should we be using this drug? Sergey and I have already talked about the potential benefits and the potential harms. I mentioned opioids and some of the concerns about that. For this drug, if we’re using it in the prehospital setting in this little green whistle, the potential benefits look really good, and we haven’t seen any of the potential harms come through in the literature.
This was another line of evidence of why this might be a good drug, because of the environmental impact of this low-dose methoxyflurane. They compared it with nitrous oxide and said, “Well, what about the life-cycle impact on the environment of using this and the overall cradle-to-grave environmental impacts?”
Obviously, Sergey and I are interested in patient care, and we treat patients one at a time. But we have a larger responsibility to social determinants of health, like our environment. If you look at the overall cradle-to-grave environmental impact of this drug, it was better than for nitrous oxide when looking specifically at climate-change impact. That might be another reason, another line of argument, that could be put forward in the United States to say, “We want to have a healthy environment and a healthy option for patients.”
I’ll let Sergey speak to mechanisms of action and those types of things.
Dr. Motov: As a general anesthetic and hydrocarbonated volatile ones, I’m just going to say that it causes this generalized diffuse cortical depression, and there are no particular channels, receptors, or enzymes we need to worry much about. In short, it’s an inhaled gas used to put patients or people to sleep.
Over the past 30 or 40 years — and I’ll go back to the past decade — there have been numerous studies in different countries (outside of the United States, of course), and with the recent study that Ken just cited, there were comparisons for managing predominantly acute traumatic injuries in pediatric and adult populations presenting to EDs in various regions of the world that compared Penthrox, or the green whistle, with either placebo or active comparators, which included parenteral opioids, oral opioids, and NSAIDs.
The recent systematic review by Fabbri, out of Italy, showed that for ultra–short-term pain — we’re talking about 5, 10, or 15 minutes — inhaled methoxyflurane was found to be equal or even superior to standard of care, primarily related to parenteral opioids, and safety was off the hook. Interestingly, with respect to analgesia, they found that geriatric patients seemed to be responding more, with respect to changing pain score, than younger adults — we’re talking about ages 18-64 vs 65 or older. Again, we need to make sure that we carefully select those elderly people without underlying renal or hepatic insufficiency.
To wrap this up, there is evidence clearly supporting its analgesic efficacy and safety, even in comparison to commonly used and traditionally accepted analgesic modalities that we use for managing acute pain.
US Military Use and Implications for Civilian Practice
Dr. Glatter: Do you think that methoxyflurane’s use in the military will help propel its use in clinical settings in the US, and possibly convince the FDA to look at this closer? The military is currently using it in deployed combat veterans in an ongoing fashion.
Dr. Motov: I’m excited that the Department of Defense in the United States has taken the lead, and they’re being very progressive. There are data that we’ve adapted to the civilian environment by use of intranasal opioids and intranasal ketamine with more doctors who came out of the military. In the military, it’s a kingdom within a kingdom. I don’t know their relationship with the FDA, but I support the military’s pharmacologic initiative by honoring and disseminating their research once it becomes available.
For us nonmilitary folks, we still need to work with the FDA. We need to convince the FDA to let us study the drug, and then we need to pile the evidence within the United States so that the FDA will start looking at this favorably. It wouldn’t hurt and it wouldn’t harm. Any piece of evidence will add to the existing body of literature that we need to allow this medication to be available to us.
Safety Considerations and Aerosolization Concerns
Dr. Glatter: Its safety in children is well established in Australia and throughout the world. I think it deserves a careful look, and the evidence that you’ve both presented argues for the use of this prehospital but also in hospital. I guess there was concern in the hospital with underventilation and healthcare workers being exposed to the fumes, and then getting headaches, dizziness, and so forth. I don’t know if that’s borne out, Ken, in any of your experience in Canada at all.
Dr. Milne: We currently don’t have it in our shop. It’s being used in British Columbia right now in the prehospital setting, and I’m not aware of anybody using it in their department. It’s used prehospital as far as I know.
Dr. Motov: I can attest to it, if I may, because I had familiarized myself with the device. I actually was able to hold it in my hands. I have not used it yet but I had the prototype. The way it’s set up, there is an activated charcoal chamber that sits right on top of the device, which serves as the scavenger for exhaled air that contains particles of methoxyflurane. In theory, but I’m telling how it is in practicality, it significantly reduces occupational exposure, based on data that lacks specifics.
Although most of the researchers did not measure the concentration of methoxyflurane in ambient air within the treatment room in the EDs, I believe the additional data sources clearly stating that it’s within or even below the detectable level that would cause any harm. Once again, we need to honor pathology. We need to make sure that pregnant women will not be exposed to it.
Dr. Milne: In 2024, we also need to be concerned about aerosolizing procedures and aerosolizing treatments, and just take that into account because we should be considering all the potential benefits and all the potential harms. Going through the COVID-19 pandemic, there was concern about transmission and whether or not it was droplet or aerosolized.
There was an observational study published in 2022 in Austria by Trimmel in BMC Emergency Medicine showing similar results. It seemed to work well and potential harms didn’t get picked up. They had to stop the study early because of COVID-19.
We need to always focus in on the potential benefits, the potential harms; where does the science land? Where do the data lie? Then we move forward from that and make informed decisions.
Final Thoughts
Dr. Glatter: Are there any key takeaways you’d like to share with our audience?
Dr. Milne: One of the takeaways from this whole conversation is that science is iterative and science changes. When new evidence becomes available, and we’ve seen it accumulate around the world, we as scientists, as a researcher, as somebody committed to great patient care should revisit our positions on this. Since there is a prohibition against this medication, I think it’s time to reassess that stance and move forward to see if it still is accurate today.
Dr. Motov: I wholeheartedly agree with this. Thank you, Ken, for bringing this up. Good point.
Dr. Glatter: This has been a really informative discussion. I think our audience will certainly embrace this. Thank you very much for your time; it’s much appreciated.
Dr. Glatter is an assistant professor of emergency medicine at Zucker School of Medicine at Hofstra/Northwell in Hempstead, New York. He is a medical adviser for Medscape and hosts the Hot Topics in EM series. Dr. Milne is an emergency physician at Strathroy Middlesex General Hospital in Ontario, Canada, and the founder of the well-known podcast The Skeptics’ Guide to Emergency Medicine (SGEM). Dr. Motov is professor of emergency medicine and director of research in the Department of Emergency Medicine at Maimonides Medical Center in Brooklyn, New York. He is passionate about safe and effective pain management in the emergency department, and has numerous publications on the subject of opioid alternatives in pain management. Dr. Glatter, Dr. Milne, and Dr. Motov had no conflicts of interest to disclose.
A version of this article appeared on Medscape.com.
This discussion was recorded on March 29, 2024. The transcript has been edited for clarity.
Robert D. Glatter, MD: Joining me today to discuss the use of methoxyflurane (Penthrox), an inhaled nonopioid analgesic for the relief of acute pain, is Dr. William Kenneth (Ken) Milne, an emergency physician at Strathroy Middlesex General Hospital in Ontario, Canada, and the founder of the well-known podcast The Skeptics’ Guide to Emergency Medicine (SGEM).
Also joining me is Dr. Sergey Motov, an emergency physician and research director at Maimonides Medical Center in Brooklyn, New York, and an expert in pain management. I want to welcome both of you and thank you for joining me.
RAMPED Trial: Evaluating the Efficacy of Methoxyflurane
Dr. Glatter: Ken, your recent post on Twitter [now X] regarding the utility of Penthrox in the RAMPED trial really caught my attention. While the trial was from 2021, it really is relevant regarding the prehospital management of pain in the practice of emergency medicine, and certainly in-hospital practice. I was hoping you could review the study design but also get into the rationale behind the use of this novel agent.
William Kenneth (Ken) Milne, MD, MSc: Sure. I’d be happy to kick this episode off with talking about a study that was published in 2020 in Academic Emergency Medicine. It was an Australian study by Brichko et al., and they were doing a randomized controlled trial looking at methoxyflurane vs standard care.
They selected out a population of adults, which they defined as 18-75 years of age. They were in the prehospital setting and they had a pain score of greater than 8. They gave the participants methoxyflurane, which is also called the “green whistle.” They had the subjects take that for their prehospital pain, and they compared that with whatever your standard analgesic in the prehospital setting would be.
Their primary outcome was how many patients had at least 50% reduction in their pain score within 30 minutes. They recruited about 120 people, and they found that there was no statistical difference in the primary outcome between methoxyflurane and standard care. Again, that primary outcome was a reduction in pain score by greater than 50% at 30 minutes, and there wasn’t a statistical difference between the two.
There are obviously limits to any study, and it was a convenience sample. This was an unmasked trial, so people knew if they were getting this green whistle, which is popular in Australia. People would be familiar with this device, and they didn’t compare it with a sham or placebo group.
Pharmacology of Penthrox: Its Role and Mechanism of Action
Dr. Glatter: The primary outcome wasn’t met, but certainly secondary outcomes were. There was, again, a relatively small number of patients in this trial. That said, there was significant pain relief. I think there are issues with the trial, as with any trial limitations.
Getting to the pharmacology of Penthrox, can you describe this inhaled anesthetic and how we use it, specifically its role at the subanesthetic doses?
Sergey M. Motov, MD: Methoxyflurane is embedded in the green whistle package, and that whole contraption is called Penthrox. It’s an inhaled volatile fluorinated hydrocarbon anesthetic that was predominantly used, I’d say 40, 50 years ago, for general anesthesia and slowly but surely fell out of favor due to the fact that, when used for prolonged duration or in supratherapeutic doses, there were cases of severe or even fatal nephrotoxicity and hepatotoxicity.
In the late ‘70s and early ‘80s, all the fluranes came on board that are slightly different as general anesthetics, and methoxyflurane started slowly falling out of favor. Because of this paucity and then a subsequent slightly greater number of cases of nephrotoxicity and hepatotoxicity, [the US Food and Drug Administration] FDA made a decision to pull the drug off the market in 2005. FDA successfully accomplished its mission and since then has pretty much banned the use of inhaled methoxyflurane in any shape, form, or color in the United States.
Going back to the green whistle, it has been used in Australia probably for about 50-60 years, and has been used in Europe for probably 10-20 years. Ken can attest that it has been used in Canada for at least a decade and the track record is phenomenal.
We are using subanesthetic, even supratherapeutic doses that, based on available literature, has no incidence of this fatal hepatotoxicity or nephrotoxicity. We’re talking about 10 million doses administered worldwide, except in the United States. There are 40-plus randomized clinical trials with over 30,000 patients enrolled that prove efficacy and safety.
That’s where we are right now, in a conundrum. We have a great deal of data all over the world, except in the United States, that push for the use of this noninvasive, patient-controlled nonopioid inhaled anesthetic. We just don’t have the access in North America, with the exception of Canada.
Regulatory Hurdles: Challenges in FDA Approval
Dr. Glatter: Absolutely. The FDA wants to be cautious, but if you look at the evidence base of data on this, it really indicates otherwise. Do you think that these roadblocks can be somehow overcome?
Dr. Milne: In the 2000s and 2010s, everybody was focused on opioids and all the dangers and potential adverse events. Opioids are great drugs like many other drugs; it depends on dose and duration. If used properly, it’s an excellent drug. Well, here’s another excellent drug if it’s used properly, and the adverse events are dependent on their dose and duration. Penthrox, or methoxyflurane, is a subtherapeutic, small dose and there have been no reported cases of addiction or abuse related to these inhalers.
Dr. Glatter: That argues for the point — and I’ll turn this over to you, Sergey — of how can this not, in my mind, be an issue that the FDA can overcome.
Dr. Motov: I agree with you. It’s very hard for me to speak on behalf of the FDA, to allude to their thinking processes, but we need to be up to speed with the evidence. The first thing is, why don’t you study the drug in the United States? I’m not asking you to lift the ban, which you put in 2005, but why don’t you honor what has been done over two decades and at least open the door a little bit and let us do what we do best? Why don’t you allow us to do the research in a controlled setting with a carefully, properly selected group of patients without underlying renal or hepatic insufficiency and see where we’re at?
Let’s compare it against placebo. If that’s not ethical, let’s compare it against active comparators — God knows we have 15-20 drugs we can use — and let’s see where we’re at. Ken has been nothing short of superb when it comes to evidence. Let us put the evidence together.
Dr. Milne: If there were concerns decades ago, those need to be addressed. As science is iterative and as other information becomes available, the scientific method would say, Let’s reexamine this and let’s reexamine our position, and do that with evidence. To do that, it has to have validity within the US system. Someone like you doing the research, you are a pain research guru; you should be doing this research to say, “Does it work or not? Does this nonapproval still stand today in 2024?”
Dr. Motov: Thank you for the shout-out, and I agree with you. All of us, those who are interested, on the frontiers of emergency care — as present clinicians — we should be doing this. There is nothing that will convince the FDA more than properly and rightly conducted research, time to reassess the evidence, and time to be less rigid. I understand that you placed a ban 20 years ago, but let’s go with the science. We cannot be behind it.
Exploring the Ecological Footprint of Methoxyflurane
Dr. Milne: There was an Austrian study in 2022 and a very interesting study out of the UK looking at life-cycle impact assessment on the environment. If we’re not just concerned about patient care —obviously, we want to provide patients with a safe and effective product, compared with other products that are available that might not have as good a safety profile — this looks at the impact on the environment.
Dr. Glatter: Ken, can you tell me about some of your recent research regarding the environmental effects related to use of Penthrox, but also its utility pharmacologically and its mechanism of action?
Dr. Milne: There was a really interesting study published this year by Martindale in the Emergency Medicine Journal. It took a different approach to this question about could we be using this drug, and why should we be using this drug? Sergey and I have already talked about the potential benefits and the potential harms. I mentioned opioids and some of the concerns about that. For this drug, if we’re using it in the prehospital setting in this little green whistle, the potential benefits look really good, and we haven’t seen any of the potential harms come through in the literature.
This was another line of evidence of why this might be a good drug, because of the environmental impact of this low-dose methoxyflurane. They compared it with nitrous oxide and said, “Well, what about the life-cycle impact on the environment of using this and the overall cradle-to-grave environmental impacts?”
Obviously, Sergey and I are interested in patient care, and we treat patients one at a time. But we have a larger responsibility to social determinants of health, like our environment. If you look at the overall cradle-to-grave environmental impact of this drug, it was better than for nitrous oxide when looking specifically at climate-change impact. That might be another reason, another line of argument, that could be put forward in the United States to say, “We want to have a healthy environment and a healthy option for patients.”
I’ll let Sergey speak to mechanisms of action and those types of things.
Dr. Motov: As a general anesthetic and hydrocarbonated volatile ones, I’m just going to say that it causes this generalized diffuse cortical depression, and there are no particular channels, receptors, or enzymes we need to worry much about. In short, it’s an inhaled gas used to put patients or people to sleep.
Over the past 30 or 40 years — and I’ll go back to the past decade — there have been numerous studies in different countries (outside of the United States, of course), and with the recent study that Ken just cited, there were comparisons for managing predominantly acute traumatic injuries in pediatric and adult populations presenting to EDs in various regions of the world that compared Penthrox, or the green whistle, with either placebo or active comparators, which included parenteral opioids, oral opioids, and NSAIDs.
The recent systematic review by Fabbri, out of Italy, showed that for ultra–short-term pain — we’re talking about 5, 10, or 15 minutes — inhaled methoxyflurane was found to be equal or even superior to standard of care, primarily related to parenteral opioids, and safety was off the hook. Interestingly, with respect to analgesia, they found that geriatric patients seemed to be responding more, with respect to changing pain score, than younger adults — we’re talking about ages 18-64 vs 65 or older. Again, we need to make sure that we carefully select those elderly people without underlying renal or hepatic insufficiency.
To wrap this up, there is evidence clearly supporting its analgesic efficacy and safety, even in comparison to commonly used and traditionally accepted analgesic modalities that we use for managing acute pain.
US Military Use and Implications for Civilian Practice
Dr. Glatter: Do you think that methoxyflurane’s use in the military will help propel its use in clinical settings in the US, and possibly convince the FDA to look at this closer? The military is currently using it in deployed combat veterans in an ongoing fashion.
Dr. Motov: I’m excited that the Department of Defense in the United States has taken the lead, and they’re being very progressive. There are data that we’ve adapted to the civilian environment by use of intranasal opioids and intranasal ketamine with more doctors who came out of the military. In the military, it’s a kingdom within a kingdom. I don’t know their relationship with the FDA, but I support the military’s pharmacologic initiative by honoring and disseminating their research once it becomes available.
For us nonmilitary folks, we still need to work with the FDA. We need to convince the FDA to let us study the drug, and then we need to pile the evidence within the United States so that the FDA will start looking at this favorably. It wouldn’t hurt and it wouldn’t harm. Any piece of evidence will add to the existing body of literature that we need to allow this medication to be available to us.
Safety Considerations and Aerosolization Concerns
Dr. Glatter: Its safety in children is well established in Australia and throughout the world. I think it deserves a careful look, and the evidence that you’ve both presented argues for the use of this prehospital but also in hospital. I guess there was concern in the hospital with underventilation and healthcare workers being exposed to the fumes, and then getting headaches, dizziness, and so forth. I don’t know if that’s borne out, Ken, in any of your experience in Canada at all.
Dr. Milne: We currently don’t have it in our shop. It’s being used in British Columbia right now in the prehospital setting, and I’m not aware of anybody using it in their department. It’s used prehospital as far as I know.
Dr. Motov: I can attest to it, if I may, because I had familiarized myself with the device. I actually was able to hold it in my hands. I have not used it yet but I had the prototype. The way it’s set up, there is an activated charcoal chamber that sits right on top of the device, which serves as the scavenger for exhaled air that contains particles of methoxyflurane. In theory, but I’m telling how it is in practicality, it significantly reduces occupational exposure, based on data that lacks specifics.
Although most of the researchers did not measure the concentration of methoxyflurane in ambient air within the treatment room in the EDs, I believe the additional data sources clearly stating that it’s within or even below the detectable level that would cause any harm. Once again, we need to honor pathology. We need to make sure that pregnant women will not be exposed to it.
Dr. Milne: In 2024, we also need to be concerned about aerosolizing procedures and aerosolizing treatments, and just take that into account because we should be considering all the potential benefits and all the potential harms. Going through the COVID-19 pandemic, there was concern about transmission and whether or not it was droplet or aerosolized.
There was an observational study published in 2022 in Austria by Trimmel in BMC Emergency Medicine showing similar results. It seemed to work well and potential harms didn’t get picked up. They had to stop the study early because of COVID-19.
We need to always focus in on the potential benefits, the potential harms; where does the science land? Where do the data lie? Then we move forward from that and make informed decisions.
Final Thoughts
Dr. Glatter: Are there any key takeaways you’d like to share with our audience?
Dr. Milne: One of the takeaways from this whole conversation is that science is iterative and science changes. When new evidence becomes available, and we’ve seen it accumulate around the world, we as scientists, as a researcher, as somebody committed to great patient care should revisit our positions on this. Since there is a prohibition against this medication, I think it’s time to reassess that stance and move forward to see if it still is accurate today.
Dr. Motov: I wholeheartedly agree with this. Thank you, Ken, for bringing this up. Good point.
Dr. Glatter: This has been a really informative discussion. I think our audience will certainly embrace this. Thank you very much for your time; it’s much appreciated.
Dr. Glatter is an assistant professor of emergency medicine at Zucker School of Medicine at Hofstra/Northwell in Hempstead, New York. He is a medical adviser for Medscape and hosts the Hot Topics in EM series. Dr. Milne is an emergency physician at Strathroy Middlesex General Hospital in Ontario, Canada, and the founder of the well-known podcast The Skeptics’ Guide to Emergency Medicine (SGEM). Dr. Motov is professor of emergency medicine and director of research in the Department of Emergency Medicine at Maimonides Medical Center in Brooklyn, New York. He is passionate about safe and effective pain management in the emergency department, and has numerous publications on the subject of opioid alternatives in pain management. Dr. Glatter, Dr. Milne, and Dr. Motov had no conflicts of interest to disclose.
A version of this article appeared on Medscape.com.