Abstracts

Rationale: The choice of antiepileptic drugs (AEDs ) varies according to clinical setting and sociodemographic factors. Few studies have examined the use of AEDs in Canadians with epilepsy. We examined the type of AED, associated side effects, and recommendations to switch AEDs in a large consecutive cohort of patients seen in an epilepsy tertiary care program. Methods: The University of Calgary Division of Neurology is the main tertiary referral centre for adults with epilepsy, serving 1.3 million people. We prospectively captured data on all consecutive adults with the diagnosis of epilepsy at the first encounter in the outpatient epilepsy program, using a validated data capture and verification system. We analyzed current and past use of AEDs, proportion of patients with side effects on each AED, predictors of side effects, and recommendations to change AEDs after the 1st encounter. Descriptive and cross correlation statistics were used to assess pertinent associations. Results: In 687 consecutive patients (52% women) the mean age and duration of epilepsy was 40 and 12 years respectively, 64.1% had focal epilepsy, 23% had idiopathic generalized epilepsy, and 21% were seizure free in the past year. At the 1st encounter, 83% were on AEDs, and of these, 71% were on monotherapy, while 21% were on 2, 6% on 3, and 2% on >4 AEDs. In the past, 48% had been on monotherapy and 52% on polytherapy. Of 18 different AEDs used, the commonest (median dose) were phenytoin (23%, 350mg), carbamazepine (21%, 800mg), valproate (13%, 1000mg), lamotrigine (12%, 200mg) and clobazam (8%, 20mg). The least commonly used AEDs (<20% of patients) were clonazepam, ethosuximide, felbamate, gabapentin, oxcarbazepine, pregabalin, primidone and vigabatrin. Side effects (SE) of AEDs occurred in 65% of patients at some point. On monotherapy, 48% had SE in the past and 28% at the initial visit. In 23%, SE occurred with every drug tried. AEDs most commonly associated with SE were phenobarbital (38%), topiramate (34%), levetiracetam (33%), carbamazepine (30%), and phenytoin (29%). Factors associated with a significantly higher risk of SE were female gender (RR 1.42, p <0.001), having a learning disorder (RR 1.4, p<0.01), and having complex partial (RR 1.2, p =0.01), generalized tonic clonic (RR 1.3, p=0.001) or absence seizures (RR 1.3, P=0.05). Factors associated with a significantly lower risk of SE were non-epileptic seizures (RR 0.45, p=0.02), and syncope (RR 0.42, p=0.003). Changes in AEDs were made in 24% of patients during the first encounter. The commonest AEDs started were lamotrigine (29%), carbamazepine (25%), levetiracetam (16%), valproate (13%), and clobazam (10%). Conclusions: Side effects were extremely common (65%) in this population, and 23% patients had SE with every AED tried. Unexpectedly, gender and learning disability are associated with a higher prevalence of side effects. Management was suboptimal in almost one quarter of patients and required AED changes during the first encounter. These findings highlight the importance of carefully assessing side effects in these patients.