Doctors are being asked to contact patients and prescribe alternatives after a class 2 recall of Emerade 500 microgram adrenaline auto-injector pens made by the Bausch & Lomb UK affiliate PharmaSwiss Česká republika.
The drugs and devices regulator MHRA said the recall is due to reports of difficulty in activating the pens because of a faulty component. This means patients may not get the adrenaline dose they need to treat anaphylaxis.
MHRA said most of the pens will still activate if more force is used when needed, and patients should also use their second pen straight away.
This recall follows similar action over Emerade 150 and 300 microgram auto-injectors in March and April. The recall was phased to ensure stocks would be available of alternative EpiPen or Jext devices.
Once issued with a new prescription for an alternative brand, patients are being told to return the old devices to a pharmacy.
An MHRA spokesperson said: "It is vital that patients follow existing advice to carry two pens with them at all times and to contact their doctor when a replacement is due.
"When switching to a different brand of adrenaline pen the patient must ensure they are familiar with how to use the pen as each brand is administered differently."
Due to COVID-19, patients are being advised to phone their GP and get the new prescription sent to the pharmacy. Face-to-face training on new devices is unlikely to be possible.
Allergy UK is reminding schools who keep pens on the premises to update their stocks.