Related Experiment Videos
Phenytoin and fluorouracil interaction
1Division of Medicine, Toowoomba Health Services, Australia.
The Annals of Pharmacotherapy
|November 29, 2001
Summary
A probable drug interaction between phenytoin and fluorouracil was observed in a patient undergoing chemotherapy. Fluorouracil likely inhibited phenytoin metabolism, leading to increased serum phenytoin levels and toxicity symptoms, necessitating dosage adjustments.
Area of Science:
- Pharmacology
- Oncology
- Drug Metabolism
Background:
- Phenytoin is an anti-epileptic drug commonly used for seizure management.
- Fluorouracil is a chemotherapeutic agent used in treating various cancers, including colon cancer.
- Drug interactions can significantly alter the efficacy and safety of medications.
Observation:
- A patient receiving phenytoin for epilepsy developed signs of phenytoin toxicity (unsteadiness, falls) after starting fluorouracil chemotherapy.
- Serum phenytoin concentration was significantly elevated (36 microg/mL) during concurrent administration.
- Phenytoin dosage reduction and monitoring led to symptom resolution and safe completion of chemotherapy.
Findings:
- Fluorouracil likely inhibits the CYP2C9 enzyme, which is responsible for metabolizing phenytoin.
- This inhibition leads to decreased clearance and increased serum concentrations of phenytoin, causing toxicity.
- This represents a newly reported drug interaction between phenytoin and fluorouracil.
Implications:
- Clinicians should be vigilant for potential phenytoin toxicity in patients receiving fluorouracil.
- Close monitoring of serum phenytoin levels and dosage adjustments are crucial during concurrent therapy.
- Further in vitro and prospective studies are needed to fully elucidate this interaction and guide clinical practice.