Concurrent lupus anticoagulants and prothrombin deficiency due to phenytoin use

A man with lupus anticoagulant and a prothrombin deficiency was studied before and after cessation of treatment with phenytoin. Multiple abnormal laboratory values of the following partially or completely resolved after the patient's therapy was discontinued: tissue thromboplastin inhibition ratio, prothrombin time, activated partial thromboplastin time, anticardiolipin antibodies, and quantitative measures and abnormal pattern on crossed immunoelectrophoresis of prothrombin. This patient represented an example of a concurrent drug-induced prothrombin deficiency and a lupus anticoagulant.