Abstracts

Rationale: Immediate release lamotrigine (LTG-IR) dosing can be limited by peak toxicity. It is thought that peak levels are responsible for some adverse effects such as dizziness, blurred vision, double vision and unsteadiness. At the same time, trough levels may be associated with reduced seizure threshold. The use of extended release lamotrigine (LTG-XR) to replace LTG-IR will be associated with lower peak levels, thus reducing adverse effects and higher trough levels, thus elevating the seizure threshold, which is expected to improve seizure control. We tested this hypothesis by analyzing seizure control and adverse effects before and after conversion from LTG-IR to LTG-XR in patients who underwent such conversion in 2009-2011. Methods: We searched our patient database to identify patients converted from LTG-IR to LTG-XR for persistent seizures or adverse effects until December 31, 2011. We excluded patients with nonepileptic seizures, progressive cause of epilepsy, or not keeping a seizure record. We collected the following parameters: age at switch, LTG-IR dose and dosing schedule, duration on that dose, LTG-XR dose and dosing schedule, LTG serum level before and after conversion, duration of LTG-XR treatment, seizure frequency before and after conversion, and change in adverse experience profile. We also recorded baseline AEDs and any AED change during the course of the analysis. Results: 55 patients (26 female) satisfied the inclusion/exclusion criteria. Their mean age was 45 years (range 23 to 86). 9 were on lamotrigine IR monotherapy and 24 took one other AED, most commonly levetiracetam. The mean dose was 544 mg/day (range 150-1100 mg/day). The mean LTG-IR serum level was 11.6 (available in 53 patients- range 4.6-21 mcg/ml). 19 patients were converted to the same dose, while 21 had their dose slightly increased and 7 had their dose slightly decreased due to adverse effects. The mean serum level after conversion was 11.8 (available in 49 patients- range 2.6-21.2). As a result of the switch, 25 patients experienced ≥50% reduction in seizure frequency, with 46% median reduction in seizure frequency. Seven patients reported improvement in adverse effects, while three reported no change. Conclusions: A switch from LTG-IR to LTG-XR can help improve seizure control in some individuals with drug-resistant epilepsy, in addition to improving tolerability. While it is indicated in individuals experiencing peak adverse effects, it should also be considered in patients who have received incomplete seizure control from LTG-IR.