Anaphylactic reaction during specific immunotherapy caused by blockade of diamine oxidase after treatment with ACC

We report the case of a male patient of 29 years with rhino-conjunctivitis allergica showing an anaphylactic reaction on the last scheduled injection of a specific immunotherapy to grass-pollen. He had well tolerated this tre atment for a period of 2 years. The patient had been treated with the bronc heolytic substance acetylcysteine prior to the therapeutic injection. Acety lcysteine is reported as an inhibitor of the histamine-degrading enzyme dia mine oxidase. We recommend to avoid acetylcysteine as well as other drugs k nown to block diamine oxidase prior to an immunotherapy injection.