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Phenytoin withdrawal and seizure frequency
E B Bromfield1, J Dambrosia, O Devinsky
1Clinical Epilepsy Section, National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892.
Neurology
|July 1, 1989
Summary
Discontinuing phenytoin in patients with complex partial seizures did not cause withdrawal seizures. Worsening seizure activity after stopping phenytoin likely indicates a loss of therapeutic effect, not abstinence.
Area of Science:
- Neurology
- Pharmacology
Background:
- Phenytoin is commonly used for epilepsy management.
- Carbamazepine is often used in combination therapy for complex partial seizures.
- Understanding drug withdrawal effects is crucial for patient care.
Purpose of the Study:
- To investigate seizure occurrence after phenytoin withdrawal in patients on combination therapy.
- To differentiate between true withdrawal seizures and loss of therapeutic effect.
Main Methods:
- Withdrawal of phenytoin from 17 inpatients on carbamazepine.
- Analysis of seizure frequency relative to plasma phenytoin levels and time since withdrawal initiation.
- Monitoring for generalized tonic-clonic seizures and seizure clusters.
Main Results:
- Seizure frequency did not correlate with initial phenytoin levels or withdrawal rate.
- Peak seizure activity occurred approximately 10 days after phenytoin levels became undetectable.
- Seizure frequency was higher during undetectable phenytoin levels compared to falling levels.
- Generalized tonic-clonic seizures occurred days after phenytoin levels became undetectable.
Conclusions:
- Phenytoin withdrawal in this patient cohort did not precipitate withdrawal seizures.
- Increased seizure activity post-discontinuation is more indicative of lost therapeutic drug effect.
- This suggests a need to re-evaluate therapeutic strategies when discontinuing phenytoin.