Phenytoin Toxicity: A Retrospective Study from a Tertiary Academic Hospital of Muscat, Sultanate of Oman

Abstract Background: Phenytoin is a widely used, cost-effective anticonvulsant with a narrow therapeutic range, requiring close monitoring to avoid toxicity. Our aim was to investigate phenytoin toxicity in an emergency department setting, focusing on clinical features, management, and outcomes. Methods: This retrospective cohort study reviewed charts from 2011 to 2021 for all cases of oral phenytoin with levels above the therapeutic range (>79.0 μmol/L or 20 mg/L). Patients were included if they exhibited clinical signs and symptoms consistent with phenytoin toxicity. Results: Of 2245 patients who had phenytoin levels sent, 264 (11.8%) had serum phenytoin levels exceeding 79.0 μmol/L; only 42 patients met the clinical inclusion criteria. Patient ages ranged from 1 to 77 years (mean: 37.7 years; standard deviation: ±24.2), with a male predominance (59.5%). Acute overdose accounted for 54.8% (23 cases). All patients presented with neurological complaints, including ataxia (50.0%), dizziness (42.9%), and seizures (33.3%). None presented with cardiological complaints. Electrocardiogram was done only for 16 patients, of whom 3 had abnormal findings. Among these 42 patients, initial phenytoin levels ranged from 82.7 to 409.7 μmol/L (mean: 130.3; interquartile range: 68.1). Only one (2.4%) patient received multiple-dose activated charcoal (MDAC). The majority (85.7%) required hospital admission. There was one (2.4%) mortality among the included patients. Conclusion: Among patients with elevated phenytoin levels, only 15.9% exhibited clinical symptoms. However, majority of these patients needed hospital admission. MDAC was underutilized as a management modality.