Abstracts

Rationale: During epilepsy monitoring unit (EMU) studies, antiepileptic drugs (AEDs) are routinely discontinued to precipitate seizures. It has been demonstrated that severe withdrawal seizures may occur after discontinuation of oxcarbazepine (OXC) and carbamazepine but not phenytoin (PHT). The aim of this study is to compare the severity and temporal pattern of withdrawal seizures after acute discontinuation of lamotrigine (LTG), levetiracetam (LEV), OXC and PHT in the EMU. Methods: We identified all patients with epilepsy who were admitted to the Vanderbilt EMU and were on LEV monotherapy, LTG monotherapy or combination LEV and LTG therapy over a period of five years. In a previous study, we similarly identified all patients on OXC or PHT monotherapy who were admitted to the EMU over a period of six years. We only included patients who had their AED of interest discontinued upon EMU admission and patients who had complex partial seizures (CPS) or generalized tonic-clonic seizures (GTCS). While LTG, LEV and PHT were abruptly discontinued, OXC was reduced to half its dose on admission day then stopped the next day. For each patient, we recorded the pre-admission seizure types and frequencies. We noted each patient s age, gender, epilepsy onset, epilepsy risk factors, AED total dose and blood levels. We then recorded the number and type of seizures for each EMU day. We compared the seizure frequency before and during the EMU admission for each seizure type. We also recorded the first seizure occurrence (any seizure, CPS or GTCS) during the EMU study for each patient.Results: A total of 141 patients (78 females) were included in our analysis. Forty patients were on OXC monotherapy, 32 patients on PHT monotherapy, 28 patients on LEV monotherapy, 10 patients on LTG monotherapy and the remaining 31 patients were on combination LEV/LTG therapy. For all groups, the mean age was 36.2 16.2 years. Mean blood levels for all four AEDs were within the accepted therapeutic range. There was no difference between AED groups in pre-EMU CPS and GTCS frequency, age of epilepsy onset or EMU study duration. The average EMU stay was 4.1 2.3 days. GTCS frequency during EMU was higher than pre-EMU baseline in all groups except for PHT (p<0.05). Six out of eight OXC patients who had GTCS during their EMU study had no prior history of GTCS, while none of the LEV, LTG or PHT patients had first-ever occurrence of GTCS in the EMU. Patients on OXC were more likely (p < 0.05) to have the first GTCS on day 1 and 2 (14/40 or 35%), compared to patients on PHT (4/32 or 12.5%) and those on LEV, LTG or LEV/LTG combination (15/69 or 21.7%). The number of GTCS peaked on EMU day 2 for OXC, day 3 for LEV, day 5 for LTG and day 6 for PHT. Conclusions: OXC withdrawal is associated with more severe GTCS compared to LEV, LTG and PHT, especially in the first two days following discontinuation. De novo GTCS may also occur after OXC withdrawal, suggesting a rebound phenomenon . Abrupt withdrawal of LTG, LEV, and PHT may be considered, while OXC needs to be tapered gradually.