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Summary
Adding aspirin to phenytoin therapy caused initial decreases in phenytoin levels, followed by significant increases. This drug interaction also led to folate deficiency and nystagmus in an epilepsy patient.
Area of Science:
- Pharmacology
- Clinical Pharmacy
- Neurology
Background:
- Phenytoin is a widely used antiepileptic drug.
- Chronic phenytoin therapy is common for epilepsy management.
- Drug interactions can significantly alter therapeutic efficacy and safety.
Observation:
- A patient on chronic phenytoin therapy experienced biphasic serum phenytoin level fluctuations upon addition of aspirin.
- Initial co-administration of aspirin led to a decrease in total serum phenytoin levels.
Findings:
- After four months of combined phenytoin-aspirin therapy, the patient exhibited elevated serum phenytoin levels.
- The patient also developed mild nystagmus and demonstrated serum folate deficiency.
- This suggests a complex pharmacokinetic interaction between aspirin and phenytoin.
Implications:
- Clinicians should monitor phenytoin levels closely when co-administered with aspirin.
- Potential for phenytoin toxicity exists with long-term combination therapy.
- Folate levels should be assessed in patients receiving chronic phenytoin and aspirin treatment.