Penthrox or Entonox? Pain Management In An Emergency Setting

What is better Penthrox or Entonox?

Before we consider which is deemed better via a systematic review and indirect treatment comparison for the management of trauma pain in an emergency setting. First lets look at the differences between Penthrox and Entonox, the cost implications and ease of use.

What is Penthrox?


Penthrox is an inhaler that contains a drug called methoxyflurane, which is poured into the device. A piece of gauze inside soaks up the liquid and you inhale the vapours. These vapours are what provide the pain relief meaning it can be used for the initial management of acute trauma pain or for brief painful procedures such as wound dressing. Penthrox is also known as the “little green whistle”.

What is Entonox?


Entonox is a well-established pain relieving gas mixture. It consists of two gases, 50% nitrous oxide (N2O) and 50% oxygen and is more commonly known as gas and air. Entonox is used to control pain during some investigations and procedures.

Is Penthrox or Entonox more Cost Effective?

A disposable Penthrox dose cost roughly the same as the refill costs of an ED Cylinder (700 Litres) of Entonox. However, this does not take into account the extra costs of using Entonox such as cylinder hire, higher delivery costs, demand value, tubing and disposable mouth pieces. When all these factors are taken into account, Penthrox seems to be the better value option – probably the reason a lot of ambulance trusts in the UK are moving over to Penthrox.

Is Penthrox or Entonox Easier to Use?

Penthrox is very lightweight (approx. 100 grams), is small enough to fit on all medical bags (approx. 15 cm long). Pentrhox is not pressurised meaning it can be transported on aeroplanes in hand luggage if needed. This makes it ideal for sports teams playing away fixtures that require air travel.

How to use Penthrox

Entonox is transported in a pressurised cylinder that weighs about 4.5kg for an ED sized cylinder. This is the size that is normally used outside hospitals in trauma settings as it has a built in regultor meaning to use all you need to do is attach the hose and a demand valve.

Click here to see BOC’s product data sheet for Entonox in the UK


In a recent study published in the US National Library of Medicine and National Institutes of Health titled “Management of trauma pain in the emergency setting: low-dose methoxyflurane or nitrous oxide? A systematic review and indirect treatment comparison” it concludes:

“Both low-dose methoxyflurane and N2O are suitable options for the pain treatment of trauma patients in the emergency setting. Due to the ease of administration and portability, inhaled low-dose methoxyflurane, however, may not only offer advantages in emergency situations in remote or difficult-to-reach locations and mass-casualty situations but also be of significant value in urban and rural environments.”

Penthrox and a wide range of pharmaceuticals and POM’s are available for UK registered Doctors to buy via Vivomed’s secure online pharmacy portal


Management of trauma pain in the emergency setting: low-dose methoxyflurane or nitrous oxide? A systematic review and indirect treatment comparison –

Penthrox –

Entonox –

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