An unexpected allergic skin reaction to peppermint oil capsules

Peppermint oil capsules are prescribed to manage abdominal colic and distension, a common complaint in postcaesarean section patients. Arachis (peanut) oil is contained within one frequently prescribed peppermint formulation: Colpermin. This ingredient is contraindicated in patients with peanut and soya allergy; however, this is not stated in the side effects or contraindications section of the British National Formulary, or present on the medication packaging. A postpartum woman in her early 30s had an unexpected allergic reaction to the capsules, in the form of a generalised body rash, fortunately with no anaphylactic features. The patient reported the same reaction to soya in the past. After review of the patient's clinical and medication history, Colpermin capsules were thought to be responsible for the patient's symptoms. This case highlights the necessity for clearer documentation in prescribing formularies and on medication packaging to ensure patient safety.