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Phenytoin/isradipine interaction causing severe neurologic toxicity
1Division of Pediatric Nephrology, University of Virginia, Charlottesville, VA 22908, USA.
The Annals of Pharmacotherapy
|August 28, 2002
Summary
A young man experienced severe neurological symptoms, including lethargy and ataxia, after starting isradipine while on phenytoin. This case highlights potential drug interactions between phenytoin and calcium-channel blockers like isradipine.
Area of Science:
- Pharmacology
- Clinical Neurology
- Drug Interactions
Background:
- Phenytoin is an antiepileptic drug used for seizure control.
- Isradipine is a calcium-channel blocker prescribed for hypertension.
- Concurrent use of multiple medications requires careful monitoring for interactions.
Observation:
- A 21-year-old male patient on phenytoin developed acute neurological symptoms including lethargy, ataxia, dysarthria, and weakness.
- These symptoms emerged shortly after initiating isradipine for essential hypertension.
- Neurological symptoms resolved upon discontinuation of isradipine.
Findings:
- Phenytoin levels remained elevated or within normal limits despite dose reductions during isradipine co-administration, indicating a pharmacokinetic interaction.
- The patient had no prior neurological issues with elevated phenytoin levels, suggesting a pharmacodynamic interaction.
- Both phenytoin and isradipine interact with calcium channels, potentially potentiating phenytoin's effects.
Implications:
- This case suggests significant pharmacokinetic and pharmacodynamic interactions between phenytoin and isradipine.
- Caution is advised when prescribing calcium-channel blockers concurrently with phenytoin.
- Further research into the combined use of anticonvulsants and calcium-channel blockers is warranted.