Batches of medication are being recalled from suppliers after they were found to contain an extra tablet.

Nitrofurantoin is prescribed to treat and prevent such as cystitis. It kills bacteria by entering their cells and damaging their genetic material.

The drug is sold by CNX Therapeutics in blister packs of capsules, which contain powder and two yellow tablets.

But some packs have been found to contain an additional yellow tablet alongside the capsule.

A notice issued by the Medicines and Healthcare products Regulatory Agency said this was "from the manufacturing process and not from broken capsules".

Suppliers are being asked to quarantine all products with two specific batch numbers, which were distributed in December.

The MHRA notice said: "Should a patient present a pack containing an extra tablet, the tablet may be removed and the patient assured that the capsule is safe to take stating the extra tablet did not come from the capsule."

Patients who find an affected packet were advised to return it to the pharmacy they got it from.

The MHRA added: "Patients that have taken the additional tablet with the capsule have ingested a higher dose of nitrofurantoin than was intended, however, the effects are understood and this should not have caused harm.

"Patients who experience adverse reactions or have any questions about the medication should seek medical attention."

Side effects of nitrofurantoin include an upset stomach, although this can be prevented by taking it with or straight after food.

It can also turn your pee dark yellow or brown, with colour returning to normal after the treatment course has ended.