title: Acute vancomycin-dependent immune thrombocytopenia as an anamnestic response.
abstract: Drug-related thrombocytopenia is a well-described but relatively rare complication of antibiotic therapy. In this entity, platelet destruction is immune-mediated, often resulting in a precipitous drop in platelet count over a short period of time. Most of these cases of thrombocytopenia are drug-dependent, as discontinuation of the offending agent frequently results in a timely return to baseline, pre-exposure platelet levels. We report the case of a 61-year-old male patient receiving vancomycin and ceftazidime for lower extremity wet gangrene who experienced a marked, acute reduction in platelet count 12 to 15 hours after starting antibiotic therapy. There was no readily apparent clinical or laboratory explanation for his thrombocytopenia. Pre- and post- antibiotic serum samples were preserved and sent for drug-dependent platelet antibody analysis. The pre-exposure specimen revealed the presence of IgG vancomycin-dependent platelet antibodies, while the post-exposure specimen demonstrated both IgG and IgM vancomycin-dependent platelet antibodies. Ceftazidime-dependent platelet antibodies were not identified in either sample. These findings indicate prior sensitization to vancomycin, with subsequent acute production of IgM anti-platelet antibodies after re-exposure to the antibiotic. The patient's antibiotics were held after the acute-onset of thrombocytopenia with subsequent restoration of normal platelet counts within 4 days of drug withdrawal, and the patient at no time experienced significant adverse bleeding events. Antibiotic therapy with vancomycin is a rare and perhaps overlooked cause for new-onset thrombocytopenia in hospitalized patients. This case illustrates that the development of severe thrombocytopenia within hours of vancomycin administration does not rule out drug-related immune clearance, as the rapid platelet destruction may indicate an anamnestic antibody response to the drug after previous exposure. In such a scenario, immediate discontinuation of vancomycin is recommended to improve platelet counts. From a laboratory perspective, retrieval of serum both pre- and post-administration of vancomycin is most helpful in determining a patient's drug-immunization status and can help guide safe drug use during future infections.
authors.affiliation: Department of Laboratory Medicine, Yale University School of Medicine, New Haven, CT 06520, USA. barton.kenney@yale.edu
authors.forename: Barton
authors.initials: B
authors.lastname: Kenney
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Tormey
mesh_terms: D000208:Acute Disease; D000671:Amputation, Surgical; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000009:adverse effects* / Q000276:immunology / Q000627:therapeutic use; D016824:Antigens, Human Platelet / Q000276:immunology; D001323:Autoantibodies / Q000276:immunology; D016470:Bacteremia / Q000188:drug therapy; D002442:Ceftazidime / Q000008:administration & dosage / Q000627:therapeutic use; D004359:Drug Therapy, Combination; D005534:Foot Diseases / Q000188:drug therapy; D016908:Gram-Positive Bacterial Infections / Q000188:drug therapy; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology*; D007075:Immunoglobulin M / Q000096:biosynthesis / Q000276:immunology*; D007156:Immunologic Memory; D008297:Male; D008875:Middle Aged; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000139:chemically induced* / Q000276:immunology; D013530:Surgical Wound Infection / Q000188:drug therapy; D014640:Vancomycin / Q000008:administration & dosage / Q000009:adverse effects* / Q000276:immunology / Q000627:therapeutic use
chemical_list: D000900:Anti-Bacterial Agents; D016824:Antigens, Human Platelet; D001323:Autoantibodies; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D014640:Vancomycin; D002442:Ceftazidime