Suspected β-Antagonist—Induced Thrombocytopenia

Abstract

To report a case of possible beta-antagonist-induced thrombocytopenia. A 44-year-old African American woman with systemic lupus erythematosus developed thrombocytopenia. Splenic sequestration was suspected, but the rise in platelets after splenectomy was temporary. Bacterial and viral etiologies were ruled out, since thrombocytopenia continued 6 months after splenectomy. Her medications acetaminophen, amitriptyline, amlodipine, beta-antagonists, and diphenhydramine were suspected. Nadolol and labetalol were started immediately prior to splenectomy. Six months after splenectomy, the woman was hospitalized for pneumonia; the platelet count was 50 x 10(3)/mm(3). Nadolol was discontinued on day 2. Within 24 hours, the platelet count rose to 128 x 10(3)/mm(3) and exceeded 200 x 10(3)/mm(3) by day 7. Labetalol was discontinued on day 8, but no additional significant rise occurred. The patient developed thrombocytopenia one year later when placed on nadolol and famotidine during admission for a gastrointestinal bleed. The platelet count decreased during the admission. Both drugs were discontinued after the last platelet count (100 x 10(3)/mm(3)). The platelet count had normalized by the follow-up visit 16 days later and remained normal until the patient's death almost a year later. Thrombocytopenia is not a common adverse effect of beta-antagonist therapy. As of February 1, 2005, only 4 case reports of suspected beta-antagonist-associated thrombocytopenia have been published in English, and the medications cited are unavailable within the US. After splenectomy, the thrombocytopenia might have resolved if the beta-antagonists had not been present. Since thrombocytopenia resolved within 24 hours of discontinuation of nadolol, it is likely that the continued thrombocytopenia was beta-antagonist induced. The likelihood that the beta-antagonist caused the adverse event is possible according to the Naranjo probability scale. The temporal association between the discontinuation of nadolol and the rise in platelets suggests that the thrombocytopenia resulted from nadolol.