Rh blood group-specific antibodies in immune hemolytic anemia induced by nomifensine

Nomifensine (Merital, Alival; Hoechst, Frankfurt, FRG), an antidepressant drug, may cause immune hemolytic anemia (IHA) of the so- called immune complex type that is believed to occur by means of an innocent-bystander mechanism. In this report we describe findings that are not consistent with this mechanism in a patient with nomifensine- induced intravascular IHA associated with renal failure. In vitro studies showed a transitory positive direct antiglobulin test (DAT) due to IgG, IgM, and C3 fixation. The causative antibodies were found to be a drug-independent IgM antibody in the serum and eluate that reacted only with E-positive RBC, although the patient's RBC were E-negative; an IgG antibody in the serum and initial eluates that showed a stronger reaction with e-positive than with e-negative or Rhnull RBC, but only in the presence of ex vivo antigen (ie, urine containing the drug and all its metabolites); and an IgM antibody in the serum and initially also on the patient's RBC that, in the presence of ex vivo antigen as well as in the presence of known metabolites of the drug, agglutinated all RBC equally strongly, but was hemolytically more active against E- positive than E-negative cells. Within a few days of stopping the drug the hemolysis rapidly resolved without administration of prednisone, the DAT became negative with anti-IgG and anti-IgM, and the drug- independent anti-E disappeared, but both metabolite-dependent antibodies remained detectable in the patient's serum. We conclude that the production and specificity of the causative antibodies in this case were controlled by a larger antigenic site, presumably consisting of the drug and/or its metabolites plus RBC antigens, rather than by epitopes of the drug or metabolites alone.