[Thrombocytopenia in digitoxin poisoning]

Because she felt unwell, an 80-year-old woman who was receiving treatment with digitoxin (0.07 mg daily) raised the dose on her own initiative to twice or three times the previous level. She then experienced faintness, visual abnormalities and bradyarrhythmia (rate about 40/min). The ECG showed 2 degrees AV block. The digitoxin level was 70.8 ng/ml--far above the upper limit of the therapeutic range (7.5-25 ng/ml). One striking abnormality was thrombocytopenia (33,000/microliters), though the white and red cell counts were normal. Petechiae were not present and there was no evidence of internal bleeding. As the AV block had not produced any critical fall in ventricular rate, there was no need to start treatment with digitalis-binding antibody fragments (Fab fragments). Instead, the patient was given cholestyramine 4 g three times daily with the aim of interrupting the enterohepatic circulation of digitoxin. From then on the rise in platelet count paralleled the fall in digitoxin level. Seven days after discontinuing digitoxin the platelet count reentered the normal range (147,000/microliters). However, the digitoxin level (39.5 mg/ml) was still well above the therapeutic range.