Phenytoin Intoxication in a Patient Receiving a Therapeutic Dose for Postoperative Seizure Prophylaxis: A Case Study
Issued Date
2023-10-01
Resource Type
eISSN
15363694
Scopus ID
2-s2.0-85171240576
Pubmed ID
37705408
Journal Title
Therapeutic drug monitoring
Volume
45
Issue
5
Start Page
573
End Page
575
Rights Holder(s)
SCOPUS
Bibliographic Citation
Therapeutic drug monitoring Vol.45 No.5 (2023) , 573-575
Suggested Citation
Prasertsup W., Chomchai S., Mekavuthikul P., Phuditshinnapatra J. Phenytoin Intoxication in a Patient Receiving a Therapeutic Dose for Postoperative Seizure Prophylaxis: A Case Study. Therapeutic drug monitoring Vol.45 No.5 (2023) , 573-575. 575. doi:10.1097/FTD.0000000000001129 Retrieved from: https://repository.li.mahidol.ac.th/handle/20.500.14594/90140
Title
Phenytoin Intoxication in a Patient Receiving a Therapeutic Dose for Postoperative Seizure Prophylaxis: A Case Study
Author's Affiliation
Other Contributor(s)
Abstract
OBJECTIVE: Phenytoin is commonly prescribed to prevent postoperative seizures. Despite the rarity of the CYP2C9 genetic polymorphism, which may result in poor phenytoin metabolism, in the Thai population, the authors report a case of phenytoin toxicity in a patient with poor metabolism administered with a standard dose of phenytoin. CASE REPORT: A 58-year-old Thai woman presented to the outpatient clinic with a 2-day history of nausea, vomiting, and dizziness. She underwent craniotomy for tumor removal 2 weeks after being diagnosed with tuberculum sellae meningioma. After the surgery, she was prescribed 300 mg of phenytoin daily to prevent seizures. During the physical examination, ataxia, horizontal nystagmus, and cerebellar abnormalities were observed, with an initial serum phenytoin concentration of 58.85 mg/L. The brain imaging results were unremarkable. Omeprazole was the only recognized drug interaction; however, it is highly unlikely to account for this condition. Pharmacogenetic investigation of CYP2C9 revealed a homozygous CYP2C9*3/*3 mutation, which is indicative of suboptimal drug metabolism and can reduce phenytoin metabolism by 50%. This patient was administered repeated dosages of activated charcoal over the course of 2 days. Her symptoms eventually subsided, with the phenytoin levels dropping to 29.51 mg/L. CONCLUSIONS: In the absence of an overdose history or drug-drug interaction, CYP2C9 polymorphism should be suspected in patients with phenytoin toxicity. In such situations, the phenytoin dosage must be decreased and monitored closely.