Phenytoin-Induced Severe Thrombocytopenia: A Case Report

Abstract

Phenytoin is a commonly prescribed antiepileptic medication for the prevention and treatment of tonic-clonic or partial seizures. Thrombocytopenia is a rare and serious adverse effect of phenytoin. This case report presents the case of a patient with severe thrombocytopenia induced by phenytoin for the treatment of tonic-clonic seizures. A 63-year-old male received 300 mg/day of phenytoin for the treatment of tonic-clonic seizures. Seven days after receiving the first dose of phenytoin, he was diagnosed with severe thrombocytopenia (platelet count 44 x 10⁹/L) without hemorrhage. Phenytoin was discontinued, and seizures were controlled with levetiracetam. Seven days after stopping phenytoin, his daily platelet count improved from 44 to 177 x 10⁹/L. The Naranjo algorithm score of 7 was at a probable level for phenytoin-induced thrombocytopenia. Thrombocytopenia is a serious adverse drug reaction that can result in life-threatening bleeding. Phenytoin-induced thrombocytopenia commonly begins 1-90 days after administration, and the recovery time is 3-21 days. The potential mechanism of phenytoin-induced thrombocytopenia is drug-induced immune thrombocytopenia. Drugs that enhance the concentration of phenytoin epoxide may be a contributing factor in phenytoin-induced thrombocytopenia. Phenytoin-induced thrombocytopenia is a rare but serious hematological complication. It should be recognized early, particularly in patients with a high risk of hemorrhage or concurrently with medications that increase phenytoin epoxide. Regularly consecutive complete blood count tests may be essential in order to detect an early decrease in platelet count in these patients.

Keywords: antiepileptic drug; drug-induced thrombocytopenia; phenytoin; phenytoin induced thrombocytopenia; thrombocytopenia.

Figure 1. Relationship between platelet count and drug administration