About Penthrox

Penthrox is a pain-relieving medicine that patients breathe in through a small, green plastic device. (The device is sometimes called a 'green whistle'.)

The device contains an active anaesthetic substance called methoxyflurane.

We use Penthrox when a patient needs pain control for up to 1 hour. For example during a short procedure (such as applying a cast) which lasts around 20 minutes.

Pain relief is almost immediate and continues for several minutes after stopping use.

Use with children

In the UK Penthrox is currently licensed only for use with adults.

However, many hospitals in the UK and other countries use it, under strict guidelines, to give pain relief to children (aged 5 to 18), often in Emergency Departments. 

Benefits

The benefits of using Penthrox are as follows.

  • It gives strong, short-acting pain relief.
  • It allows your child to self-administer pain relief.
  • It can reduce the need to give pain relieving injections using needles.

Preparing for Penthrox

Before we use Penthrox, we will check that you are confident your child will be able to use the device.

We will also check that it is safe for them.

We do not use Penthrox if your child:

  • is allergic to, or has reacted badly to anaesthetic before
  • has a family history of getting a high fever after anaesthetic (malignant hyperthermia)
  • has serious kidney or liver problems
  • has heart or circulation issues
  • has recently taken or is taking certain medications. These include:
    • strong painkillers
    • some antibiotics
    • anticonvulsants
    • antivirals
    • sedative antihistamines

Let us know about every regular or recent medication which your child uses.

Let us know if your child has been given Penthrox at any time during the last 7 days.

How to use Penthrox

We will show your child how to:

  • put the inhaler mouthpiece between their teeth, with their lips closed around it.
  • breathe in and out, as normal, through the mouthpiece.

Pain relief usually starts after 6 to 10 breaths.

Penthrox has a strong fruity smell and taste. The first few breaths may cause coughing, which quickly settles.  

Important

Your child must breathe in and out through the device.

This stops the pain relief medication from releasing into the air.

Side effects

Mild side effects

Most side effects are mild and disappear within minutes of stopping use. Common side effects:  

  • headache
  • dizziness
  • dry mouth
  • drowsiness
  • feeling sick (nausea)
  • tingling skin
  • double vision
  • flushed or irritated skin.

If you are concerned about any side effects, we will take the device away from your child. In this situation, we will consider using a different type of pain relief.

Serious side effects

Serious side effects are rare.

They may include :

  • allergic reactions
  • liver problems
  • kidney problems. 

When to seek medical help

If your child becomes unwell or has any difficulty breathing, call NHS 111 or go to your nearest Emergency Department (A&E). 

Tell the medical staff that your child has recently used Penthrox. 

Contact information

Kingston Hospital Emergency Department (A&E)