A hypertensive patient started on high-dose intravenous antibiotic therapy develops hemolytic anemia two weeks later. Direct antiglobulin test is positive, and elution studies show the antibody binds only to red cells pre-incubated with the drug. Which drug classically produces hemolysis by this hapten-mediated mechanism?
- A Methyldopa
- B Quinine
- C Penicillin ✓
- D Ceftriaxone
Correct answer: C. Penicillin
Explanation
High-dose penicillin coats red cell membranes, and antidrug antibodies bind the drug-red cell complex, producing extravascular hemolysis; the antibody reacts only against drug-coated cells, defining the hapten mechanism. Methyldopa induces true autoantibodies that react with untreated RBCs as well. Quinine and cephalosporins such as ceftriaxone act via the innocent bystander mechanism, where drug-antibody immune complexes adsorb onto red cells and activate complement, often causing abrupt intravascular hemolysis.
Reference: Williams Hematology, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.