Changes in the coagulation system during pseudoallergic anaphylactoid reactions to drugs and food additives

In 10 patients with known anaphylactoid reactions to drugs and food additives, oral provocation tests were performed with increasing doses of the implicated agents. Clinical reactions, vital signs, bleeding time, prothrombin time, partial thromboplastin time and platelet aggregation were measured before and 15 min after each oral dose. Six patients reacted clinically. In all 10 patients, platelet aggregation decreased with increasing challenging doses. All other parameters remained stable or changed without any correlation to the drug, the type or the severity of the reaction. Measurement of the bleeding time is, therefore, of no diagnostic value in anaphylactoid reactions, and major alterations in the coagulation system do not explain their pathogenesis.