Immune Complex Formation Involving Etoricoxib in a Patient with Acute Severe Anemia

Background: DIIHA (Drug-induced immune hemolytic anemia) is rare, and a specialized laboratory is often required to provide optimal serological tests to confirm diagnosis. There have been few cases reported of etoricoxib-induced immune hemolytic anemia. Immune complexes formed between some drugs and their respective antibodies attach weakly or strongly in a nonspecific way to RBCs (red blood cells). The bound immune complex activates complement, which may lead to hemolysis in vivo. Aims: Demonstration of immune complex formation involving etoricoxib in vitro. Methods: A 46-year-old woman developed acute severe anemia one day after a single dose of etoricoxib 90 mg per os with a strong positive DAT (direct anti-globulin test) and a weak positive IAT (indirect anti-globuline test). For investigation diagnosis, we used the American Association of Blood Banks Technical Manual protocol using patient serum collected in three different moments (at patient admission, one month after and one month after stopping steroids). Results: The authors found strong positive IAT reactions when the patient serum was tested with the drug. Conclusions: The strong agglutination that occurred in the mixture of the drug and the patient serum indicates a drug/antidrug interaction and may lead to DIIHA. This was the first case reported in Portugal of DIIHA induced by etoricoxib.