Beware excipients: Anaesthetic considerations for a patient with metabisulphite allergy

ABSTRACT

Allergy to excipients used in drug formulations is an often overlooked issue, recently highlighted by cases of severe reaction to the Pfizer-Biontech COVID-19 vaccination. Sulphites, including metabisulphites, are antioxidant preservatives found in many foods but also in certain drugs used by anaesthetists, including metaraminol, catecholamines, metoclopramide and some forms of propofol. Patients may present with a variety of intolerances to sulphites. Anaesthetists need to know how to counsel them, which drugs to avoid, and whether to administer sulphite-containing adrenaline in an emergency scenario. Description A patient with reported sulphite allergy following previous reactions to metabisulphite-containing local anaesthetic presented for an elective operation. The hospital pharmacist took several weeks to confirm the sulphite content of key anaesthetic drugs and to find alternatives. In particular, sulphite-free adrenaline had to be sourced from France. General anaesthesia proceeded uneventfully, and a 'green bag' of safe emergency drugs stayed with the patient until her discharge. The patient was referred for further allergy testing, but as the allergy centre could not provide sulphite-free adrenaline, she declined challenge with metabisulphites and with preparations of adrenaline available in the UK. This will clearly pose a challenge in the future should she present with anaphylaxis or for emergency surgery or critical care. Discussion Documented reactions to parenteral sulphites are uncommon, varied and cover a variety of suggested pathophysiologies, of which IgE-mediated allergy is rare [1]. Additionally, asthmatics may report bronchospasm related to sulphite containing foodstuffs, but this results from direct irritation from sulphur dioxide and is not immune mediated. Establishing the diagnosis is difficult, requiring challenge testing in specialist allergy centres;skin prick testing can be unreliable. Challenge with sulphite-containing adrenaline, thus establishing safety of use in case of anaphylaxis, is one pragmatic option. Sensible precautions include close liaison with the hospital pharmacist, an easily accessible list of sulphite-free alternatives and a policy on adrenaline use in anaphylaxis. Although evidence is scant, expert opinion suggests that in anaphylaxis the benefit of administering sulphite-containing adrenaline outweighs the risks [2].