Consumer medicine information




Brand name

Penthrox Inhalation

Active ingredient





Consumer medicine information (CMI) leaflet

Please read this leaflet carefully before you start using Penthrox.

What is this leaflet?

This leaflet answers some of the common questions people ask about PENTHROX® (methoxyflurane). It does not contain all the information known about PENTHROX®.

It does not take the place of talking to your healthcare professional (i.e., doctor, dentist, pharmacist, nurse, etc.).

All medicines have risks and benefits. Your healthcare professional has weighed the risks of you being given PENTHROX® against the benefits they expect it will have for you.

If you have any concerns about being given this medicine, ask your healthcare professional.

Keep this leaflet in a safe place. You may need to read it again.

What PENTHROX® is used for

PENTHROX® is a medicine which is used to reduce pain.

It is inhaled through the PENTHROX® INHALER.

Pain relief should start after 6-10 breaths. PENTHROX® is intended to reduce the severity of pain, rather than completely eliminate it.

PENTHROX® belongs to a family of medicines called inhalation anaesthetics. At the recommended dose, PENTHROX® provides pain relief without producing anaesthesia.

Ask your healthcare professional if you have any questions about why PENTHROX® has been prescribed for you.

Before you are given PENTHROX®

When you must not be given it

You must not be given PENTHROX® if you have an allergy to methoxyflurane, other inhalation anaesthetics or any of the ingredients listed at the end of this leaflet.

Symptoms of an allergic reaction may include:

  • Shortness of breath, wheezing or difficultly to breathe
  • Swelling of the face, lips, tongue or other parts of the body
  • Rash, itching or hives on the skin

You must not be given PENTHROX® if you have, or are suspected of having, an inherited tendency for a condition called malignant hyperthermia. This is a condition where, when you or a related family member has been given an anaesthetic, symptoms such as a very high fever, fast, irregular heartbeat, muscle spasms and breathing problems have occurred.

You must not be given PENTHROX® if you have heart disease, kidney disease or reduced function of your kidneys, difficulty breathing or head injury.

If you are not sure whether you should be given PENTHROX®, talk to your healthcare professional.

Before you are given it

PENTHROX® should only be used if the package is undamaged and the expiry date marked on the bottle has not passed.

Tell your healthcare professional if you have allergies to:

  • Any other medicines
  • Any other substances such as foods, preservatives or dyes
  • Any ingredients listed at the end of this information leaflet

Tell your healthcare professional if you are pregnant or intending to become pregnant. Your healthcare professional will discuss the possible risks and benefits of being given PENTHROX® during pregnancy.

Tell your healthcare professional if you are breast-feeding or intending to breast-feed. Your healthcare professional will discuss the possible risks and benefits of being given PENTHROX® during breast-feeding.

Tell your healthcare professional if you have, or have had, any medical conditions, especially the following:

  • Kidney problems
  • Liver problems

If you have not told your healthcare professional about any of the above, tell them before you are given PENTHROX®. You may still be able to use PENTHROX®, but your healthcare professional will need to assess the risks against the potential benefits.

Taking other medicines

Tell your healthcare professional if you are taking any other medicines, including medicines that you buy without a prescription at the chemist, supermarket or health food shop.

Some medicines and PENTHROX® may interfere with each other. Your healthcare professional needs to know if you are taking any of these medicines to accurately assess the risks and benefits of administering PENTHROX®. These include:

  • Isoniazid to treat tuberculosis
  • Barbiturates, such as phenobarbital to treat epilepsy
  • Rifampicin to treat infection
  • Medicines, or illegal drugs, that have a dampening effect on the nervous system such as narcotics.
  • Antibiotics or other medicines that may harm the kidney such as tetracycline, gentamicin, kanamycin, colistin, polymyxin B, cephaloridine or, amphotericin B
  • Intravenous adrenaline
  • β-blockers to treat hypertension

Your doctor may have more information on medicines to be careful with around the time you receive PENTHROX®.

How PENTHROX® is given

How much is given

One bottle of PENTHROX® (1.5 mL or 3 mL) to be used initially. Additional bottle(s) may be used if required. The maximum recommended dosage is 6 mL of PENTHROX® per day and 15 mL per week. PENTHROX® should not be used on consecutive days. You should not inhale more than the maximum dose because PENTHROX® may damage your kidneys.

How the PENTHROX® Inhaler is given

  1. Your healthcare professional will prepare the PENTHROX® Inhaler (with or without the optional Activated Carbon (AC) Chamber), and place wrist loop over your wrist.

  1. Breathe in through the mouthpiece of the PENTHROX® Inhaler to obtain pain relief. Your healthcare professional will show you how if you are unsure. Accustom yourself to the fruity smell of the medicine by inhaling gently for the first few breaths. You must breathe out through the PENTHROX® Inhaler when the AC Chamber is attached for the AC Chamber to adsorb any exhaled methoxyflurane. After the first few breaths, breathe normally through the PENTHROX® Inhaler. Pain relief should commence after approximately 6-10 consecutive breaths.
After the initial 6-10 breaths, you can inhale PENTHROX® continuously or intermittently as instructed by your healthcare professional. For intermittent dosing, a top-up of 6 breaths may be given before each of the more painful parts of a procedure.

  1. If you need stronger pain relief, cover the dilutor hole on the PENTHROX® Inhaler or on the AC Chamber with your finger during use. Your healthcare professional will show you where the dilutor hole is.

  1. You do not need to breathe in through the PENTHROX® Inhaler all of the time. Your healthcare professional will encourage you to take breaks from the PENTHROX® Inhaler as this will increase the duration of use.

How long is it given for

Continue using your medicine until your healthcare professional tells you to stop or when you have inhaled the maximum recommended dose.

One 3 mL bottle of PENTHROX® provides approximately 20-25 minutes of pain relief when inhaled continuously. A second 3 mL bottle of PENTHROX® can be given to extend the period of pain relief to approximately 50-55 minutes when inhaled continuously. Intermittent inhalation will increase the time of analgesia.

How is it given

PENTHROX® is poured into the base of the PENTHROX® Inhaler by the healthcare professional and is absorbed into the wick. You will inhale PENTHROX® either directly from the PENTHROX® Inhaler.


The healthcare professional giving you PENTHROX® will be experienced in its use, so it is extremely unlikely that you will be given too much. The dose of PENTHROX® is limited by the amount contained in each bottle.

You should not use more than 6 mL in one day and not more than 15 mL in one week. Administration of consecutive days is not recommended. If the maximum dose is exceeded PENTHROX® may cause irreversible damage to your kidneys.

Immediately contact your healthcare professional or the Poisons Information Centre (telephone 13 11 26) for advice, or go to Accident and Emergency at the nearest hospital, if you think that you or anyone else may have been given too much PENTHROX®. Do this even if there are no signs of discomfort or poisoning. You may need urgent medical attention.

While you are being given PENTHROX®

Things you must do

You should breathe in through the mouthpiece, initially ensuring that the “dilutor” hole of the PENTHROX® Inhaler is not covered.

Accustom yourself to the characteristic fruity smell of the PENTHROX® by inhaling gently for the first few breaths through the PENTHROX® Inhaler. You must breathe out through the PENTHROX® Inhaler, if an AC Chamber is attached.

If further relief is required you may cover the “dilutor” hole with your finger for a higher inhaled concentration of PENTHROX®.

Use PENTHROX® intermittently as required to provide pain relief.

Things you must not do

Do not give PENTHROX® to anyone else, even if they have the same condition as you.

Do not drive or operate machinery until you know how PENTHROX® affects you. PENTHROX® may cause drowsiness or dizziness in some people and therefore may affect alertness.

Make sure you know how you react to PENTHROX® before you drive a car, operate machinery, or do anything else that could be dangerous if you are drowsy, dizzy or not alert.

Things that may be helpful

You are in control of the level of your pain relief by directly inhaling PENTHROX® from the PENTHROX® Inhaler.

The aim of PENTHROX® is to relieve pain until you feel comfortable. Relief will commence after approximately 6-10 breaths. Relief will continue for several minutes after ceasing use of PENTHROX®.

Side Effects

Tell your healthcare professional as soon as possible if you do not feel well after you have been given PENTHROX®.

PENTHROX® is well tolerated, but it may occasionally have unwanted side effects. All medicines can have side effects. Sometimes they are serious, but most of the time they are not. You may need medical treatment if you have some of the side effects.

Ask your healthcare professional to answer any questions you may have.

Other side effects not listed below may occur in some patients.

Do not be alarmed by this list of possible side effects. You may not experience any of them.

If you are taking PENTHROX® for Trauma and associated pain

Tell your healthcare professional if you notice any of the following side effects and they worry you.

PENTHROX® may cause:

  • Feeling sick or nauseous
  • Dry mouth
  • Coughing (usually in the first few breaths)
  • Vomiting
  • Dizziness
  • Loss of memory
  • Headache
  • Migraine
  • Drowsiness
  • Low blood pressure
  • Feeling drunk
  • Toothache
  • Flu-like symptoms, such as high temperature, sore throat, runny nose, cough and chills
  • Viral infection
  • Nose and throat inflammation
  • Fall
  • Joint sprain
  • Increase in blood enzyme levels, including alanine aminotransferase, aspartate aminotransferase and blood lactate dehydrogenase
  • Painful menstrual periods
  • Pain in the mouth and throat
  • Rash
  • Back pain
  • Difficulty in speaking

If you require PENTHROX® for surgical procedures

Tell your healthcare professional if you notice any of the following side effects and they worry you.

PENTHROX® may cause:

  • Dizziness
  • Feeling of extreme happiness
  • Feeling sick or nauseous
  • Sweating
  • Taste disturbance or loss of taste
  • Flushing
  • High blood pressure
  • Feeling anxious
  • Depression
  • Numbness or weakness of the arms and legs
  • Drowsiness
  • Vomiting
  • Confusion

These lists include the more common side effects of PENTHROX®. They are usually mild and only last a short time.

Contact your doctor immediately if:

  • You experience any symptoms of liver problems, such as loss of appetite, nausea, vomiting, jaundice (yellowing of the skin and/or eyes), dark coloured urine, pale coloured stools, pain/ache or sensitivity to touch in your right abdominal area (below your ribs)
  • You experience any symptoms of kidney problems such as reduced or excessive urination or swelling of feet or lower legs.

Tell your healthcare professional if you notice anything else that is making you feel unwell. Other sides effects not listed above may also occur in some people. Some of these side effects (for examples changes to blood enzyme levels) can only be found when your doctor does tests from time to time to check your progress.

After being given PENTHROX® (methoxyflurane)


PENTHROX® should be carefully stored below 30°C in its original container.


Your healthcare professional will dispose of any excess PENTHROX® liquid and the PENTHROX® INHALER in the appropriate way.

Product Description

What it looks like

PENTHROX® is a clear, almost colourless liquid with a characteristic fruity smell that becomes a vapour or gas when it is used with the PENTHROX® INHALER.

PENTHROX® is supplied in the following presentations:

a) 3 mL sealed bottle with a tear off tamper-evident seal (packs of 10),

b) Combination pack with one 3 mL sealed bottle and one PENTHROX® INHALER (packs of 1 or 10), with/without optional activated carbon chamber

c) Combination pack with two 3 mL sealed bottles and one PENTHROX® INHALER (packs of 10), and

d) Combination pack with one 1.5 mL sealed bottle and one PENTHROX Inhaler (packs of 1 or 10) with AC Chamber.

Healthcare professionals can also obtain additional PENTHROX® Inhalers separately.


Active Ingredient:

  • Methoxyflurane 99.9%

There is a small amount (approximately 0.01% Butylated Hydroxy Toluene) of stabilising agent in PENTHROX®.

Manufacturer and Sponsor

Medical Developments International Limited
4 Caribbean Drive
Scoresby VIC 3179 Australia
Tel: +61 3 9547 1888

This leaflet was revised in February 2020

Australian Registration Number:
AUST R 43144

Published by MIMS May 2020


Brand name

Penthrox Inhalation

Active ingredient





1 Name of Medicine


2 Qualitative and Quantitative Composition

Each bottle contains 99.9% methoxyflurane.
Methoxyflurane belongs to the fluorinated hydrocarbon group of volatile anaesthetic agents. It is a volatile liquid intended for vaporisation and administration by inhalation using the Penthrox Inhaler. At low concentrations the inhaled vapour is used to provide analgesia in stable, conscious patients.

3 Pharmaceutical Form

Methoxyflurane is a clear, almost colourless mobile liquid, with a characteristic odour that is mildly pungent (see Section 6.7 Physicochemical Properties).

4 Clinical Particulars

4.1 Therapeutic Indications

1. For emergency relief of pain by self administration in conscious haemodynamically stable patients with trauma and associated pain, under supervision of personnel trained in its use (see Section 4.2 Dose and Method of Administration).
2. For the relief of pain in monitored conscious patients who require analgesia for surgical procedures such as the change of dressings (see Section 4.2 Dose and Method of Administration).


The total maximum dose must not be exceeded.

4.2 Dose and Method of Administration

For use only as an analgesic agent (see Section 4.3 Contraindications).


One bottle of Penthrox (1.5 mL or 3 mL) to be vaporised in a Penthrox inhaler. On finishing the initial bottle, another bottle may be used. Up to 6 mL may be administered per day. The refilling must be conducted in a well ventilated area to reduce environmental exposure to methoxyflurane vapour.
To maximise safety, the lowest effective dosage of Penthrox (methoxyflurane) to provide analgesia should be used, particularly for children and the elderly. The total weekly dose should not exceed 15 mL. Administration on consecutive days is not recommended.
The cumulative dose received by patients receiving intermittent doses of Penthrox (methoxyflurane) for painful procedures (such as wound dressings) must be carefully monitored to ensure that the recommended dose of methoxyflurane is not exceeded.
Methoxyflurane may cause renal failure if the recommended dose is exceeded. Methoxyflurane associated renal failure is generally irreversible.

Method of administration.

Penthrox (methoxyflurane) is self administered under observation (and assisted if necessary) by a person trained in its administration using the hand held Penthrox Inhaler.
Instructions on the preparation of the Penthrox Inhaler and correct administration are provided below.

How to use the Penthrox inhaler.

1. Ensure the Activated Carbon (AC) chamber (where applicable) is inserted into the dilutor hole on the top of the Penthrox Inhaler.
2. Holding the methoxyflurane bottle upright, use the base the Penthrox Inhaler to loosen the cap with a ½ turn. Separate the inhaler from the bottle and remove the cap by hand.
3. Tilt the Penthrox Inhaler to a 45° angle and pour the contents of one bottle into the base whilst rotating.
4. Place wrist loop over patient's wrist. Patient inhales through the mouthpiece of inhaler to obtain analgesia. First few breaths should be gentle and then breathe normally through inhaler.
5. Patient exhales into inhaler. The exhaled vapour passes through the AC chamber to adsorb any exhaled methoxyflurane.
6. If stronger analgesia is required, patient can cover dilutor hole with finger during inhalation.
7. Patient should be instructed to inhale intermittently to achieve adequate analgesia. Continuous administration will reduce time of analgesia. Patients should be administered minimum dose.
8. Replace cap onto Penthrox bottle. Place used Penthrox Inhaler and used bottle in sealed plastic bag and dispose of responsibly (see Section 6.6 Special Precautions for Disposal).

4.3 Contraindications

Use as an anaesthetic agent.
Renal impairment, including reduced glomerular filtration rate (GFR), urine output and reduced renal blood flow.
Renal failure.
Hypersensitivity to fluorinated anaesthetics or any ingredients in Penthrox.
Cardiovascular instability.
Respiratory depression.
Head injury or loss of consciousness.
A history of possible adverse reactions in either patient or relatives.
Malignant hyperthermia: patients with known or genetically susceptible to malignant hyperthermia.

4.4 Special Warnings and Precautions for Use

Use in hepatic impairment.

It is advisable not to administer methoxyflurane to patients who have shown signs of liver damage, especially after previous methoxyflurane or halothane anaesthesia.
There have also been occasional reports of hepatic dysfunction, jaundice, and fatal hepatic necrosis associated with methoxyflurane use.

Renal impairment.

Methoxyflurane impairs renal function in a dose related manner due to the effect of the released fluoride on the distal tubule and may cause polyuric or oliguric renal failure, oxaluria being the prominent feature.
Because of the potential nephrotoxic effects methoxyflurane must not be used as an anaesthetic agent. The risk is related to the total dose (time and concentration) and frequent exposure. Methoxyflurane impairs renal function in a dose related manner.
Nephrotoxicity is greater with methoxyflurane than with other halogenated anaesthetics because of the slower metabolism over several days resulting in prolonged production of fluoride ions and metabolism into other potentially nephrotoxic substances. Therefore the lowest effective dose of methoxyflurane should be administered, especially in aged or obese patients.
Daily use of methoxyflurane is not recommended because of nephrotoxic potential.

Diabetic patients.

Diabetic patients may have an increased likelihood of developing nephropathy if they have impaired renal function or polyuria, are obese or are not optimally controlled.

Use in the elderly.

Caution should be exercised in the elderly due to possible reduction in blood pressure or heart rate.

Paediatric use.

Limited data is available regarding the administration of methoxyflurane using the Penthrox Inhaler. The minimum effective dose to produce analgesia should be administered to children.

Paediatric neurotoxicity.

Some published studies in children have observed cognitive deficits after repeated or prolonged exposures to anaesthetic agents early in life. These studies have substantial limitations, and it is not clear if the observed effects are due to the anaesthetic/analgesic/sedation drug administration or other factors such as the surgery or underlying illness.
Published animal studies of some anaesthetic/analgesic/sedation drugs have reported adverse effects on brain development in early life and late pregnancy. The clinical significance of these nonclinical finding is yet to be determined.
With inhalation or infusion of such drugs, exposure is longer than the period of inhalation or infusion. Depending on the drug and patient characteristics, as well as dosage, the elimination phase may be prolonged relative to the period of administration.

Occupational exposure.

Health workers who are regularly exposed to patients using Penthrox inhalers should be aware of any relevant occupational health and safety guidelines for the use of inhalational agents. The use of methods to reduce occupational exposure to methoxyflurane, including the attachment of the Penthrox Activated Carbon (AC) chamber, should be considered. Multiple use creates additional risk. Elevation of liver enzymes, blood urea nitrogen and serum uric acid have been reported in exposed maternity ward staff.

Effects on laboratory tests.

No data available.

4.5 Interactions with Other Medicines and Other Forms of Interactions

The concurrent use of tetracycline and methoxyflurane for anaesthesia has been reported to result in fatal renal toxicity. The possibility exists that methoxyflurane may enhance the adverse renal effects of other drugs including certain antibiotics of known nephrotoxic potential such as gentamicin, kanamycin, colistin, polymyxin B, cephaloridine and amphotericin B. Dosage for the subsequent administration of narcotics may be reduced.
Concomitant use of Penthrox with CNS depressants e.g. opioids may produce additive depressant effects. If opioids are given concomitantly with Penthrox, the patient should be observed closely, as is normal clinical practice with opioids.
It is possible that enzyme inducers (such as barbiturates, alcohol, isoniazid, phenobarbital or rifampicin) which increase the rate of methoxyflurane metabolism might increase its potential toxicity and they should be avoided concomitantly with methoxyflurane.
Intravenous adrenaline or nor-adrenaline should be employed cautiously during methoxyflurane administration.
Interactions may occur with β-blockers, with an increased risk of hypotension.

4.6 Fertility, Pregnancy and Lactation

Effects on fertility.

No data available.
(Category C)
Published animal studies of some anaesthetic/analgesic/sedation drugs have reported adverse effects on brain development in early life and late pregnancy.
Published studies in pregnant and juvenile animals demonstrate that the use of anaesthetic/analgesic and sedation drugs that block NMDA receptors and/or potentiate GABA activity during the period of rapid brain growth or synaptogenesis may result in neuronal and oligodendrocyte cell loss in the developing brain and alterations in synaptic morphology and neurogenesis when used for longer than 3 hours. These studies included anaesthetic agents from a variety of drug classes.
All general anaesthetics cross the placenta and carry the potential to produce central nervous system and respiratory depression in the newborn infant. In routine practice this dose does not appear to be a problem; however in a compromised foetus, careful consideration should be given to this potential depression, and to the selection of anaesthetic drugs, doses and techniques.
Neonates delivered of mothers who used methoxyflurane analgesia for childbirth had a briefly raised serum uric acid, not requiring further intervention.

Toxaemia of pregnancy.

It is advisable not to administer methoxyflurane due to the possibility of existing renal impairment.
Caution should be exercised when methoxyflurane is administered to a nursing mother.

4.7 Effects on Ability to Drive and Use Machines

The decision as to when patients may again engage in activities requiring complete mental alertness, operate hazardous machinery or drive a motor vehicle must be individualised. Patients should be warned to take extra care as a pedestrian and not to drive a vehicle or operate a machine until the patient has completely recovered from the effects of the drug, such as drowsiness. The treating doctor should decide when activities such as driving a vehicle or operating a machine may be resumed.

4.8 Adverse Effects (Undesirable Effects)

There are no data on the dose dependency of most of the adverse drug reactions.

Use of Penthrox in patients with trauma and associated pain.

Table 1 provides treatment emergent adverse events experienced by ≥ 1% of the safety population of a placebo controlled study in patients with trauma and associated pain, of which 149 had Penthrox.
In listings below, are adverse reactions (adverse effects that are related to the treatment) which occurred at a rate lower than in Table 1. They are listed by system organ class and frequency (common ≥ 1/100 to < 1/10; uncommon ≥ 1/1,000 to < 1/100; and rare ≥ 1/10,000 to < 1/1,000).

Nervous system disorders.

Uncommon: dysgeusia, paraesthesia.

Gastrointestinal disorders.

Uncommon: oral discomfort.

General disorders and administration site conditions.

Uncommon: fatigue, feeling abnormal, feeling of relaxation, hangover, hunger, shivering.

Eye disorders.

Uncommon: diplopia.

Psychiatric disorders.

Uncommon: inappropriate affect.

Use of Penthrox for pain relief in patients who require it for surgical procedures.

Table 2 provides drug associated events (adverse reactions) experienced by ≥ 2% of the safety population of a placebo controlled study in patients in a minor surgical procedure, of which 49 had Penthrox for the relief of pain.


The following additional adverse effects have also been reported in the literature in association with analgesia.

Nervous system disorders.

Altered state of consciousness, nystagmus.

Respiratory, thoracic and mediastinal disorders.

Choking, hypoxia.

Hepatobiliary disorders.

Hepatic failure, hepatitis, jaundice, liver injury.

Renal and urinary disorders.

Renal failure.

Eye disorders.

Vision blurred.

Psychiatric disorders.

Affect lability, agitation, confusional state, dissociation, restlessness.

Vascular disorders.

Blood pressure fluctuation.


Blood uric acid increased, blood urea increased, blood creatinine increased, hepatic enzymes increased.
Hepatic toxicity in association with methoxyflurane is rare but has been observed with analgesic use.
The following adverse effects have been reported in association with historical use as an anaesthetic.
(i) Common: retrograde amnesia, nausea, vomiting, coughing, drowsiness, sleeping, dizziness, dislike of odour, fever, polyuria, headache.
ii) Rare: nonspecific hepatitis, malignant hyperthermia.
iii) Other reported events: cardiac arrest, respiratory depression, laryngospasm, bronchospasm, hypotension, bradycardia, renal failure, increased serum urea, increased serum creatinine, increased urinary oxalate excretion, increased serum inorganic fluoride, pallor, muscle relaxation.

Reporting suspected adverse effects.

Reporting suspected adverse reactions after registration of the medicinal product is important. It allows continued monitoring of the benefit-risk balance of the medicinal product. Healthcare professionals are asked to report any suspect adverse reactions at

4.9 Overdose

Adverse effects will include those for anaesthetic doses, see Section 4.8 Adverse Effects (Undesirable Effects).
Patients should be observed for signs of drowsiness, pallor and muscle relaxation following methoxyflurane administration.
In the event of excessive urinary output following overdosage, fluid and electrolyte losses should be promptly replaced.
For information on the management of overdose, contact the Poison Information Centre on 13 11 26 (Australia).

5 Pharmacological Properties

5.1 Pharmacodynamic Properties

Mechanism of action.

Methoxyflurane vapour provides analgesia when inhaled at low concentrations. After methoxyflurane administration, drowsiness may occur. During methoxyflurane administration, the cardiac rhythm is usually regular. The myocardium is only minimally sensitised to adrenaline by methoxyflurane. In light planes of anaesthesia some decrease in blood pressure may occur. This may be accompanied by bradycardia. The hypotension noted is accompanied by reduced cardiac contractile force and reduced cardiac output.

Clinical trials.

No data available.

5.2 Pharmacokinetic Properties


Methoxyflurane is more susceptible to metabolism than other halogenated methyl ethyl ethers and has greater propensity to diffuse into fatty tissues. Hence methoxyflurane is released slowly from this reservoir and becomes available for biotransformation for many days.


Biotransformation of methoxyflurane occurs in man. As much as 50-70% of the absorbed dose is metabolised to free fluoride, oxalic acid, difluoromethoxyacetic acid, and dichloroacetic acid. Both the free fluoride and the oxalic acid can cause renal damage in large doses, however dose related nephrotoxicity seen with clinical doses appears related to a combination of free fluoride and dichloroacetic acid.


Approximately 20% of methoxyflurane uptake is recovered in the exhaled air, while urinary excretion of organic fluorine, fluoride and oxalic acid accounts for about 30% of the methoxyflurane uptake. Studies have shown that higher peak blood fluoride levels are obtained earlier in obese than in nonobese and in the elderly.

5.3 Preclinical Safety Data


No data available.


No data available.

6 Pharmaceutical Particulars

6.1 List of Excipients

Butylated Hydroxytoluene.

6.2 Incompatibilities

Incompatibilities were either not assessed or not identified as part of the registration of this medicine.

6.3 Shelf Life

In Australia, information on the shelf life can be found on the public summary of the Australian Register of Therapeutic Goods (ARTG). The expiry date can be found on the packaging.

6.4 Special Precautions for Storage

Store below 30°C.

6.5 Nature and Contents of Container

Penthrox (methoxyflurane) is supplied in the following presentation: a) 3 mL sealed bottle with a tear off tamper seal (pack of 10);
b) Combination pack with one 3 mL sealed bottle and one Penthrox Inhaler (pack of 1 or 10) with or without optional Activated Carbon (AC) Chamber;
c) Combination pack with two 3 mL sealed bottles and one Penthrox Inhaler (pack of 10); and
d) Combination pack with one 1.5 mL sealed bottle and one Penthrox Inhaler (pack of 1 or 10) with AC Chamber.

6.6 Special Precautions for Disposal

In Australia, any unused medicine or waste material should be disposed of in accordance with local requirements.

6.7 Physicochemical Properties

Methoxyflurane is known chemically as 2,2-dichloro-1,1-difluoro-1-methoxyethane. The molecular formula is C3H4Cl2F2O and the molecular weight is 164.97. Methoxyflurane is soluble 1 in 500 of water; miscible with alcohol, acetone, chloroform, ether and fixed oils. It is soluble in rubber. The flash point in oxygen is 32.8°C. The concentration to reach flash point is usually not achieved under normal circumstances.
Some of the physical constants are in Table 3.
Methoxyflurane is stable and does not decompose in contact with soda lime. An antioxidant, Butylated Hydroxy Toluene (0.01% w/w) is added to ensure stability on standing. As polyvinyl chloride plastics are extracted by methoxyflurane, contact should be avoided. Methoxyflurane does not extract polyethylene plastics, polypropylene plastics, fluorinated hydrocarbon plastics or nylon.
The vapour concentration of methoxyflurane is limited by its vapour pressure at room temperature to a maximum of about 3.5% at 23°C. In practice, this concentration is not reached due to the cooling effect of vaporisation. Methoxyflurane is not flammable except at vapour concentrations well above those recommended for its use. Recommended concentrations are non-flammable and non-explosive in air and oxygen at ordinary room temperature.

Chemical structure.

CAS number.


7 Medicine Schedule (Poisons Standard)