Abstracts

Rationale: Lamotrigine is an effective antiepileptic drug that is usually well-tolerated. Although many patients become seizure-free at low doses, others require continued titration as long as seizures recur with no adverse effects. In the process of titration, some patients may experience toxicity manifesting with vertigo, ataxia, and diplopia, among other symptoms. Patients presenting to the emergency room with these symptoms often immediately receive a stroke alert evaluation. Lamotrigine serum concentration is often ordered after a negative stroke workup, or if ordered in a timely manner the result is not available until days later. Methods: We searched our patient data base to identify adult patients treated with lamotrigine who presented with dizziness, unsteadiness, or diplopia and received a negative stroke evaluation. We excluded patients with known history of vertebrobasilar insufficiency or stroke or vestibular disease. The following parameters were collected: date of occurrence, age at time of occurrence, symptoms presented, imaging studies performed including brain CT/MRI/MRA/CTA/CTP, dose of lamotrigine, if a serum concentration was ordered and the time it was available. Results: Out of 972 patients on lamotrigine, 14 patients met the inclusion/exclusion criteria. One patient had two separate negative stroke evaluations for what turned out to be lamotrigine toxicity. The cost of imaging for each evaluation ranged from ~ $2000-3500. The mean age was 61 years (range 43-79) as compared to 47 years for all patients treated with lamotrigine. The mean daily lamotrigine dose was 621 mg (range 300 ?" 900mg). A lamotrigine serum concentration was requested on the day of evaluation in 8 patients, though the result was never available until at least the next day. The serum concentration ranged from 17-28 mcg/ml. In 6 patients (7 instances of toxicity) the level was not performed at the time of evaluation. Conclusions: Lamotrigine peak toxicity often manifests with dizziness/vertigo, ataxia and diplopia, which can imitate posterior circulation ischemia. Emergency rooms will frequently call a stroke alert and obtain expensive imaging, particularly in seniors at greater risk of stroke. It is also likely that seniors are more susceptible to experience peak lamotrigine adverse effects. Lamotrigine serum concentrations are either not obtained or if obtained are not immediately available. We recommend that a rapid lamotrigine assay be made available and always ordered in patients receiving lamotrigine, avoiding the considerable expense of an un-necessary stroke evaluation. Funding: none