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Penthrox Inhalation

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Generic Name: Methoxyflurane
Product Name: Penthrox Inhalation


Penthrox is an analgesic, which is a medication used to relieve pain. It is usually prescribed for people who experience pain following an injury or who will undergo painful procedures associated with surgery such as dressing changes.


The active ingredient in Penthrox, methoxyflurane, works by affecting the brain and spinal cord and making them less responsive to excitement and pain.

Dose advice

Dose information

The correct dose for each individual is the lowest possible dose that provides adequate pain relief. Your doctor will determine the correct dose for you.

The maximum recommended dose of Penthrox is 15 mL per week. Up to 6 mL can be administered as a single dose, but usually 3 mL is given each time. The dose is taken using an inhaler.

Penthrox should not be taken two days in a row.


The Penthrox inhaler should be prepared by a trained health professional. Preparation involves pouring the Penthrox medicine into the inhaler.


Penthrox inhalation is self-administered through the inhaler, meaning that the person taking the medicine uses the inhaler themselves. However, they are always monitored by a health professional who has been trained to administer the drug.

When the inhalation device is prepared, the person taking the medicine straps it to their wrist using a wrist strap and places the inhaler in their mouth. Most people breathe through the inhaler mouth piece; however, a face mask can be used to assist inhalation if this is difficult.

When the inhaler is in place, they begin by breathing gently for the first couple of breaths, until they become accustomed to the smell of the inhalation. They can then begin breathing normally, but should inhale through the inhaler intermittently when they require pain relief, not continuously. During intermittent inhalations, a 3 mL bottle of Penthrox provides pain relief for 20–25 minutes.

It is also important to exhale through the inhaler so that left over medicine is exhaled into and absorbed by the activated carbon chamber attached to the inhaler. This prevents the medicine escaping into the air and being breathed in by other people.

Dose concentration

The concentration of the dose can be adjusted using the dilution hole in the inhaler. When the dilution hole is open, the Penthrox inhaler delivers lower concentrations of the active ingredient, methoxyflurane. When a finger is held over the dilution hole to close it, the inhaler delivers the medicine in a more concentrated form, which provides greater pain relief. The doctor will advise you whether or not you should close the dilution hole or leave it open.

Important considerations

Penthrox causes drowsiness and may impair your ability to drive a car or operate machinery. Exercise caution when carrying out potentially dangerous activities like crossing the road. Do not drive or operate machinery while affected by Penthrox. Your doctor will advise when it is safe to resume driving and other activities.

Penthrox sometimes causes side effects, and it is important to seek medical advice immediately if you experience any sickness, as it may be related to the medicine. Contact your doctor or hospital immediately if you experience any of the following symptoms:

  • Jaundice (yellowing of skin);
  • Vomiting;
  • Nausea;
  • Loss of appetite;
  • Darkened urine;
  • Pale stools;
  • Pain or sensitivity in the right abdomen, just below the ribs.
  • Reduced urine output;
  • Swollen feet; or
  • Swollen lower legs.

Tell your doctor if you feel unwell following Penthrox administration, as the sickness may be a side effect of the medicine.

If you have any queries about the correct way to use Penthrox, please ask your doctor.


Penthrox should not be used under certain conditions. Tell your doctor if you have:

  • Allergies to methoxyflurane (the active ingredient), other inhalation anaesthetics, or one the inactive ingredients in Penthrox;
  • History or family history of an allergic reaction to an anaesthetic medicine. Symptoms of an allergic reaction include shortness of breath, swelling and rash;
  • Kidney disorder: Penthrox impairs kidney function and is dangerous for people with existing kidney disorders;
  • Heart problems;
  • Problems breathing;
  • Head injury;
  • History or family history of malignant hyperthermia. This includes symptoms of a very high fever, shortness of breath, fast irregular heartbeat and muscle spasms following the intake of medication.


Special care needs to be taken when using Penthrox under certain conditions. Tell your doctor if you:

  • Use any other medications, including over-the-counter medications and supplements. Some medicines affect the way Penthrox works and Penthrox may affect the way other medications you use work, so it is important for the doctor to consider the possible ways in which your medications will affect each other;
  • Have a liver disorder;
  • Have diabetes;
  • Are pregnant or breastfeeding; or
  • Have recently been sick.


Penthrox is a Pregnancy Category C medication. It can pass from the pregnant woman’s body into her foetus. This may affect the central nervous system and/or breathing of the baby when it is born. This may be dangerous if the foetus is not in optimal health, so the doctor needs to carefully consider whether or not Penthrox is the most appropriate medicine and, if so, how much should be provided.


Penthox can be used by breastfeeding women. However, the doctor will be cautious about prescribing this medicine to a woman who is breastfeeding, as it can be passed on to the baby through breast milk.


Penthrox can be used by children. However, there have been no studies to determine the best dose for children. The doctor will therefore use the smallest dose of Penthrox that achieves pain relief when treating a child.

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Schedule of Penthrox Inhalation:

Penthrox is a Schedule 4 medication.1

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Common side effects of Penthrox Inhalation:

All medicines have side effects. Most commonly the side effects are minor, however, some can be more serious. Usually the benefits of taking a medication outweigh the associated side effects. Your doctor would have considered these side effects before starting you on Penthrox.

Side effects of Penthrox may include:

On rare occasions, Penthrox results in serious side effects, which may include:

  • Liver toxicity, resulting in loss of appetite, yellowing of the skin (jaundice), dark coloured urine, pale coloured stools and pain in the right lower abdomen;
  • Kidney failure, causing a person to urinate less and their ankles and feet to swell.

If you experience any of the listed side effects, or any other symptoms that appear abnormal or unusual, please tell your doctor.

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  1. Penthrox Product Information. Springvale, VIC: Nycomed Pty Ltd; 9 February 2010.
  2. Penthrox Consumer Medical Information. Springvale, VIC: Nycomed Pty Ltd; February 2010.
  3. Methoxyflurane [online]. Adelaide, SA: Australian Medicines Handbook; July 2010 [cited 4 January 2011]. Available from: [URL Link]
  4. Penthrox Abbreviated PI [online]. St Leonards, NSW: MIMS Online; November 2006 [cited 10 January 2011]. Available from: [URL Link]

For further information talk to your doctor.

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Posted On: 22 July, 2003
Modified On: 20 October, 2015
Reviewed On: 12 January, 2011


Created by: myVMC