What is the EMS Inhaler for Pain? All About Penthrox (Methoxyflurane)

October 7, 2025 •

4 min read

For over 40 years, the Penthrox inhaler has been a staple for emergency pain relief in countries like Australia and New Zealand, providing a rapid, non-opioid alternative for trauma patients. This portable, self-administered device, famously known as the "green whistle," uses the active medication methoxyflurane to provide fast-acting analgesia in pre-hospital and emergency department settings.

Quick Summary

The EMS inhaler for pain is Penthrox, a device for self-administering methoxyflurane vapor for short-term pain relief in emergency situations. It provides rapid, effective, and patient-controlled analgesia for moderate to severe trauma pain, reducing the need for opioids.

Key Points

Penthrox (Methoxyflurane): The most common EMS inhaler for pain is the Penthrox device, colloquially known as the "green whistle," which contains the drug methoxyflurane.
Rapid, Self-Administered Relief: The inhaler provides patient-controlled pain relief with a rapid onset (within minutes) for short-term management of moderate to severe pain.
Non-Opioid Analgesic: It offers a valuable non-narcotic alternative to traditional opioids, reducing the risks of sedation and dependency.
Proven Safety Profile: Although initially used as an anesthetic with renal toxicity concerns, its low-dose analgesic use has been safe and widely accepted for over four decades in certain regions.
Specific Uses: It is indicated for moderate to severe pain from trauma and for minor procedural pain, not for chronic conditions.
Contraindications Exist: Use is contraindicated in patients with impaired consciousness, significant renal or liver disease, and other conditions.
Improved Efficiency: Rapid pain management with the Penthrox inhaler can improve patient satisfaction and potentially decrease emergency department length of stay.

What is the Penthrox (Methoxyflurane) Inhaler?

The EMS inhaler for pain is the Penthrox inhaler, a handheld, single-use medical device that delivers low-dose methoxyflurane vapor for analgesic purposes. Methoxyflurane is a volatile, halogenated ether that provides powerful pain relief at sub-anesthetic concentrations. Because of its distinctive color and shape, the device is colloquially known as the "green whistle".

How Penthrox Provides Rapid Pain Relief

When a patient inhales through the Penthrox device, the liquid methoxyflurane vaporizes and is absorbed by the patient's lungs. This offers a number of benefits:

Rapid onset: Patients can begin to feel pain relief within 6 to 10 breaths, with median onset times as fast as 3 to 4 minutes.
Self-administered and titrated: The patient can control the amount of medication they receive by breathing in and out as needed, or by covering the diluter hole for a stronger effect. The effects wear off quickly once inhalation stops.
Non-opioid: As a non-narcotic analgesic, it avoids many of the side effects and risks associated with opioids, such as severe respiratory depression and potential dependency.

How to Use the Green Whistle Inhaler

Proper preparation and administration are critical for safe and effective use. The process is straightforward, designed for ease of use by both patients and supervising medical personnel:

Preparation: A medical professional inserts the Activated Carbon (AC) Chamber into the top of the green whistle and pours the liquid methoxyflurane from a vial into the base of the inhaler.
Inhalation: The patient is instructed to place their mouth on the mouthpiece and breathe normally. The first few breaths should be gentle to get used to the fruity smell.
Dosage Control: For stronger pain relief, the patient can cover the diluter hole on the AC chamber with their finger while inhaling.
Intermittent Use: To prolong the duration of the medication, the patient can inhale intermittently only when pain relief is needed. The duration of analgesia can vary depending on continuous or intermittent use.
Supervision: The patient should be continuously supervised while using the inhaler to ensure they remain conscious and are using it correctly.
Disposal: After use, all components are placed in a sealed plastic bag for safe disposal.

Key Indications and Contraindications for Penthrox

Approved Uses

Penthrox is primarily used for the emergency relief of moderate to severe pain in conscious adults, particularly for trauma-related injuries. Its use is also common for managing pain during minor medical procedures in both pre-hospital and emergency department settings, such as:

Fracture or dislocation reduction
Changing painful dressings on burn patients
Pain relief during transport for injured patients

Who Cannot Use the Inhaler? (Contraindications)

Due to potential risks, the Penthrox inhaler is not suitable for all patients. Contraindications include:

Renal Impairment: Patients with pre-existing kidney disease or at risk of renal injury.
Liver Dysfunction: History of liver damage following exposure to methoxyflurane or other halogenated anesthetics.
Altered Consciousness: Patients with a decreased level of consciousness, head injuries, or those unable to cooperate.
Cardiovascular Instability: Patients with unstable hemodynamics or respiratory depression.
Malignant Hyperthermia: Personal or genetic history of this condition.
Age: In many regions, it is not approved for use in children under 18 years of age.
Drug Interactions: Concurrent use with known nephrotoxic drugs like tetracycline antibiotics.

Penthrox vs. Other EMS Pain Medications

EMS providers use a range of medications for pain management, including opioids like morphine and fentanyl, and non-opioids. The choice depends on the patient's condition and the severity of pain.


Feature	Penthrox (Methoxyflurane)	Opioids (e.g., Morphine, Fentanyl)	Ketamine
Administration	Self-administered inhalation	Injection (IV, IM) or intranasal	Injection (IV, IM)
Speed of Onset	Rapid (3-10 minutes)	Rapid (IV: <5 min; immediate for fentanyl)	Rapid (IV: 30 seconds; IM: 3-4 minutes)
Duration of Effect	Short (30-60 minutes)	Variable	Short (IV: 5-10 min; IM: 12-25 min)
Non-Opioid	Yes	No	No (dissociative anesthetic)
Patient Control	Yes, self-titration via inhaler	No, controlled by provider	No, controlled by provider
Common Side Effects	Dizziness, headache, nausea, somnolence	Nausea, vomiting, respiratory depression, sedation	Hallucinations, tachycardia, hypertension

The Global History and Safety of Methoxyflurane

Methoxyflurane was initially developed as a general anesthetic in the 1960s but was largely discontinued for this purpose by the 1970s due to concerns about dose-related nephrotoxicity (kidney toxicity). However, its use as a low-dose analgesic continued in Australia and New Zealand, demonstrating a robust safety profile at these much lower concentrations.

For over 40 years, millions of doses have been administered with a low incidence of adverse effects and no reports of significant kidney or liver toxicity at analgesic doses. The inhaler device also incorporates an activated carbon chamber to adsorb exhaled vapor, minimizing occupational exposure for supervising healthcare professionals. In recent years, Penthrox has been approved for emergency use in Europe, Canada, and other countries. This rich history and extensive real-world use support its efficacy and safety as a valuable, non-opioid pain management option in emergency care, as detailed in reviews such as this NIH/PMC resource.

Conclusion

For emergency services seeking rapid, effective, and patient-controlled pain relief, the Penthrox inhaler is a proven asset. By utilizing low-dose methoxyflurane, this non-opioid analgesic offers significant advantages in pre-hospital and emergency department settings, particularly for trauma-related pain. Its portable design and quick onset allow medics to address pain promptly, which can lead to improved patient satisfaction and potentially reduced emergency department length of stay for certain injuries. While not available in all regions (such as the US market currently undergoing trials), its long track record and favorable safety profile in countries where it is widely used solidify its status as a key tool for emergency pain management.

Frequently Asked Questions

The Penthrox inhaler contains the medication methoxyflurane, a volatile liquid that is inhaled as a vapor for its analgesic, or pain-relieving, effects.

Pain relief begins very quickly, often within 6 to 10 breaths. Clinical studies have shown a median time to first pain relief of around 3 to 4 minutes.

No, methoxyflurane is a non-opioid analgesic. This makes it a useful alternative for patients who may not tolerate or are unsuitable for opioid medications.

Methoxyflurane was used as a general anesthetic in the past but was discontinued due to reported risks of nephrotoxicity (kidney toxicity) at the high doses required for anesthesia. Its current analgesic use is at much lower, sub-anesthetic doses where this toxicity is not observed.

No, methoxyflurane was withdrawn from the US market in 2005. It is, however, widely used in Australia and New Zealand, and has recently been approved in parts of Europe and Canada.

The most common side effects are typically mild and transient, and may include dizziness, headache, nausea, and somnolence (drowsiness).

Use during pregnancy is not generally recommended unless the benefits outweigh the potential risks. It is classified as a Pregnancy Category C drug, and use during pregnancy or breastfeeding is listed as a contraindication in some regions.

No, the Penthrox inhaler is only approved for the short-term, emergency relief of moderate to severe pain. It is not intended for the management of chronic pain conditions.

The Penthrox inhaler includes an activated carbon chamber that adsorbs exhaled methoxyflurane, significantly reducing occupational exposure for supervising healthcare professionals. Use should also occur in a well-ventilated area.