Drug-drug interactions in epilepsy

A silent threat. You’d be surprised how often physicians forget the way medicines behave as chemicals in the body. There is no simple rule to follow–every drug has a unique half life, mechanism of action, and method for removal from the body.  Phenytoin, for example, is metabolized largely by the liver and is almost entirely excreted unchanged in the urine, while drugs like vigabatrin and gabapentin do not require the liver for metabolism. For a quick review from our BrainWaves podcast, check out the talk on drug-drug interactions in epilepsy:

Excess. Nearly 50% of all medications prescribed in the elderly are unnecessary. And the interactions account for an incredible number of hospitalizations every year. It’s called polypharmacy. The elderly are particularly at risk because they often see so many different physicians of various specialties. As a neurologist, I can’t remember the last time I had to know how to dose ursodiol–a drug used to prevent gallstones–how it works, or how it can interact with the medications I typically prescribe.

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Magic Pills. From https://www.flickr.com/photos/jonathansilverberg/9194590737/ under a Creative Commons license.

Patients with seizures will seize. Like clopidogrel for coronary stent management, missing doses of your anti-epileptic drugs is extremely unsafe. Non-compliance with anti-epileptic drugs is the #1 cause of recurrent seizures in patients with epilepsy. So if a patient is experiencing an undesirable side effect of the drug or serum levels of the drug are affected by other medications, your patient could end up subtherapeutic on their current regimen. Alternatively, drug-drug interactions may inadvertently elevate the serum levels of the anti-epileptic drug, risking toxicity. Therefore, it is critical for providers to recognize these major drug-drug interactions, and for patients to educate themselves on the risks of their daily pharmacologic cocktails.

 

[Jim Siegler]


The content in this episode was vetted and approved by Danielle Becker.

REFERENCES

Perucca E. Clinically relevant drug interactions with antiepileptic drugs. Br J Clin Pharmacol. 2006;61:246-255

Pennell PB, Newport DJ, Stowe ZN, Helmers SL, Montgomery JQ, Henry TR. The impact of pregnancy and childbirth on the metabolism of lamotrigine. Neurology. 2004;62:292-295

Petrenaite V, Sabers A, Hansen-Schwartz J. Individual changes in lamotrigine plasma concentrations during pregnancy. Epilepsy Res. 2005;65:185-188

Pennell PB, Peng L, Newport DJ, Ritchie JC, Koganti A, Holley DK, et al. Lamotrigine in pregnancy: Clearance, therapeutic drug monitoring, and seizure frequency. Neurology. 2008;70:2130-2136

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  1. September 22, 2016

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