Immune-Mediated Thrombocytopenia in Patients Treated with Vancomycin.

Numerous drugs are known to cause immune thrombocytopenia (TP) mediated by antibodies (abs) that bind to platelets only when the sensitizing drug is present in soluble form. The widely used antibiotic, vancomycin, has been implicated as a cause of TP only in 8 case reports and little is known about antibodies possibly responsible for this complication. We characterized clinical and serologic aspects of TP occurring in 39 patients during treatment with vancomycin. In this group, TP developed after 1–27 days of treatment (median 6 days) and plt nadirs ranged from 1,000 to 60,000 plts/uL (median 14,000 plts/uL). Bleeding occurred in 14 patients and contributed to a fatal outcome in 3. TP persisted for 1–17 days after discontinuing vancomycin (median 7 days). Platelets eventually returned to baseline in all surviving patients. Serum obtained after the onset of TP was studied for vancomycin-dependent, platelet-reactive abs by flow cytometry and by solid phase ELISA using immobilized plt glycoproteins (GP) as targets.

Results of flow cytometric studies are summarized above. All patients had IgG and/or IgM abs that reacted with normal plts in the presence, but not in the absence of vancomycin. The IgG mean fluorescence intensity (MFI) signal in the presence of drug was 1.6 to 32.0 times stronger (mean ratio 5.7) than that obtained in the absence of drug. Vancomycin-dependent IgG abs were also identified in 59 of 273 normal individuals but were much weaker than abs detected in patients (p = 0.004). IgM abs (mean ratio 5.7, range 1.6 – 34) were found in 18 of 39 patients (46%). Weaker IgM abs were found in only 5 of 273 normal subjects (1.8%) (p = 0.001). Two patient abs studied in ELISA reacted preferentially with GPIIb/IIIa. Studies to determine the frequency of abs in patients given vancomycin who do not develop TP are in progress.

These findings provide evidence that TP in patients given vancomycin can be caused by drug-dependent abs specific for GPIIb/IIIa that are stimulated by vancomycin exposure. IgG and IgM abs in patients with TP are generally much stronger than drug-dependent, platelet-reactive immunoglobulins found in some normal subjects. The significance of the latter abs is presently unknown. Drug-dependent IgM abs are found almost exclusively in patients with vancomycin-associated TP and may be diagnostic. Patients treated with vancomycin often have life-threatening bacterial sepsis and may have various reasons for developing TP. Serologic testing for drug-dependent, platelet-reactive IgG and IgM abs may provide a means of identifying those in whom vancomycin should be discontinued.