Drug-induced thrombocytopenia

Features:

• commonly involves quinine, quinidine, sulphonamides, certain antibiotics e.g. cephalothin, heparin
  
  
• the drug functions as a hapten, binds to the platelet, and fixes complement; intravascular lysis or removal by the reticuloendothelial system follows
  
  
• platelet count falls rapidly within 2-3 days of taking a drug which has been taken previously; or 7 or more days after starting a new drug
  
  
• count rises rapidly within 7 - 10 days of withdrawal except if drug metabolism is slow e.g. gold thiomalate, deiphenylhydantoin (Dilantin(R))
  
  
• 3-25% incidence of heparin thrombocytopenia - uniquely demonstrates paradoxical thrombosis which improves after heparin withdrawal
  
  
• chloramphenicol depresses platelet production