Inaccurate assessment of drug-induced thrombocytopenia: reason for concern

OBJECTIVE: To report two cases in which patients were reputed to have exhibited thrombocytopenia secondary to the histamine-receptor blocking agent ranitidine. Evaluation and the associated time frame of events failed to confirm these observations. DESIGN: Two case studies. RESULTS: Ranitidine was ordered as part of the therapeutic course of two patients admitted to the medicine service. The development of thrombocytopenia in both patients was attributed to this agent and it was discontinued. In addition to ranitidine, both patients received several other agents with greater potential to cause thrombocytopenia, and had a time course of development of the adverse effect that would not support ranitidine as the offending agent. Both patients required histamine-receptor antagonists at some point following their discontinuation and, based on the available evidence, the pharmacy suggested that these agents be restarted. In neither case did restarting the histamine-receptor antagonist lead to recurrence of thrombocytopenia. CONCLUSIONS: Although ranitidine can cause thrombocytopenia, the reported incidence is very low. Spontaneous reporting of adverse effects is essential in establishing a true pattern of safety for a drug. However, reports need to be scrutinized before they are rolled into the collective intelligence. Overzealous or incomplete reporting will lead to cautions that are either unnecessary or, because they deny people necessary treatment, dangerous.