What should you know about methylene blue anaphylaxis?

Methylene blue is a medicine or dye used in some medical procedures. Anaphylaxis is a rapidly developing allergic reaction that can affect breathing, blood pressure, skin and the digestive system. Warning features may include wheezing, throat or tongue swelling, hoarse voice, trouble breathing, widespread hives, dizziness, fainting, vomiting or sudden weakness. Symptoms can begin soon after exposure, but timing can vary. A reaction may occur even if you have received a medicine before without difficulty.

Stop the exposure if this can be done safely and call emergency services. If an adrenaline auto-injector has been prescribed, use it as directed and tell responders when it was given. Lie down with your legs raised unless breathing is easier sitting up; do not stand or walk suddenly. Do not rely on an antihistamine alone when breathing or circulation is affected. Emergency teams may provide oxygen, adrenaline and other treatment, followed by observation because symptoms can return.

Seek emergency help immediately for breathing difficulty, wheezing, facial or throat swelling, faintness, confusion or collapse after methylene blue. Even if symptoms improve, urgent assessment is needed. A clinician can document the suspected reaction, review the procedure record and decide whether specialist follow-up or allergy testing is appropriate.

Ask which symptoms made the reaction concerning, whether methylene blue should be recorded as an allergy, what medicines or dyes should be avoided, and whether you need an emergency action plan or referral.