A patient with autoimmune hemolytic anemia develops hemolysis after receiving high-dose intravenous penicillin. The direct antiglobulin test is positive. Which mechanism explains this drug-induced hemolysis?
- A Penicillin coating the red cell membrane, with IgG binding the haptenized cell ✓
- B IgM-mediated complement lysis triggered by immune complexes containing drug and antibody
- C Drug-induced suppression of CD55 and CD59 expression on erythrocytes
- D Direct complement activation by the antibiotic independent of antibody
Correct answer: A. Penicillin coating the red cell membrane, with IgG binding the haptenized cell
Explanation
Penicillin acts as a hapten, coating red cell membranes at high doses; IgG antibodies then bind the membrane-bound drug, producing extravascular hemolysis with a positive direct Coombs test. Cephalosporins and quinidine form soluble immune complexes that fix complement via IgM, the mechanism in option B, while penicillin-type injury is dose dependent and extravascular.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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