Table 1.

Mechanisms Underlying Drug-Induced Thrombocytopenia

Classification (drugs)	Mechanism	Incidence
Hapten-dependent antibody (penicillin, some cephalosporin antibiotics)	Hapten links covalently to membrane protein and induces drug-specific immune response	Very rare
Quinine-type drug (quinine, sulfonamide antibiotics, nonsteroidal anti-inflammatory drugs)	Drug induces antibody that binds to membrane protein in presence of soluble drug	26 cases per 1 million users of quinine per week, probably fewer cases with other drugs
Fiban-type drug (tirofiban, eptifibatide)	Drug reacts with glycoprotein αIIbβ3 to induce a conformational change recognized by antibody (not yet confirmed)	0.2%-0.5%
Drug-specific antibody (abciximab)	Antibody recognizes murine component of chimeric Fab fragment specific for platelet β3	0.5%-1.0% after first exposure,10%-14% after second exposure
Autoantibody (gold salts, procainamide)	Drug induces antibody that reacts with autologous platelets in absence of drug	1.0% with gold, very rare with procainamide and other drugs
Immune complex (heparins)	Drug binds to platelet factor 4, producing immune complex for which antibody is specific; immune complex activates platelets through Fc receptors	1%-3% among patients treated with unfractionated heparin for 7 days, rare with low-molecular-weight heparin

Table adapted from Aster and Bougie with permission from the Massachusetts Medical Society.¹⁵⁷