Severe hypotension, bronchospasm, and urticaria from intravenous indigo carmine.

Indigo carmine is generally believed to be a safe, biologically inert substance. Adverse reactions to the intravenous administration of this dye have been seen only rarely. We report a life-threatening anaphylactoid reaction to indigo carmine that may have been due to either a drug allergy or to its intrinsic serotonergic properties.