This is an observational study exploring the genetics of lacosamide response. The study will last 3 years and has been divided in to three stages; 1) recruitment, 2) observational phase, 3) genotyping and analysis. Patients initiating lacosamide are recruited and their baseline seizure frequency is assessed retrospectively. Patients are then monitored for 18 months with an assessment (via interview and where possible seizure diaries) of seizure frequency and other treatment related phenotypes every 3 months. The recruitment period will span months 1-12, the observational period will span months 1-30 and analysis of data will be conducted between months 30-36 (see Figure 2 below). Target sample size is 610.

Primary objective: To determine the clinical relevance of genetic variation in predicting lacosamide responsive and non-responsive patients.

Secondary objectives: To determine the clinical relevance of genetic variation in predicting:

• Optimal dose of lacosamide
• Adverse drug reactions to lacosamide

Inclusion Criteria:

• Diagnosed with partial onset seizures (simple and/or complex) with or without secondary generalization (based on 1981 ILAE seizure classification scheme)
• Over 18 and under 65 years of age at date of recruitment in to the study
• Currently undergoing pharmacological treatment for refractory partial epilepsy ('refractory' here refers to patients who continue to have seizures despite treatment (current) with two or more appropriate anti-epileptic drugs at appropriate doses)
• Deemed suitable for treatment with lacosamide (following drug guidelines)

Exclusion Criteria:

• Patients experiencing seizure type other than partial onset seizures (with/without secondary generalisation)
• Patients with a history of chronic alcohol or drug abuse within previous 3 years.
• Non refractory epilepsy patients
• Patients suffering any other clinically significant disease e.g. cancers, progressive neurological disorder, heart failure, respiratory failure etc
• Patients who are pregnant or who are intending on getting pregnant within the period of the trial.

patients with epilepsy recruited from five tertiary referral centres.