A Study to Evaluate XEN1101 as Adjunctive Therapy in Primary Generalized Tonic-Clonic Seizures

This study is looking for people aged 12 and older who have been diagnosed with a type of epilepsy called generalized epilepsy and specifically experience Primary Generalized Tonic-Clonic Seizures (PGTCS). You should have had these seizures for at least a year and continue to have them despite trying at least two different epilepsy medicines in the past. You should currently be taking between one and three anti-seizure medications at a steady dose.

There are also some reasons why you might not be able to join. For example, if you've had a severe, prolonged seizure (status epilepticus) in the last year, or if your seizures are caused by things like drug or alcohol use, an infection, or another serious brain condition. Also, if you mainly have seizures that start in one part of the brain (focal seizures), this study might not be suitable for you.

If you decide to take part, the study will involve several steps. Firstly, there will be a screening period lasting up to 9.5 weeks, where we'll look at how often you have seizures and confirm you meet all the study requirements. After this, you'll enter the 'double-blind treatment period' for 12 weeks. During this time, you'll take either the new medicine (XEN1101) or a placebo, once a day with your evening meal. You'll need to keep a careful record of your seizures during this time.

Throughout the study, you'll have regular visits to your study clinic for check-ups and to see how you're getting on. Once the 12-week treatment period is over, you might have the option to join another study where everyone receives XEN1101, if you wish to continue. If not, you'll have an 8-week follow-up period after you stop taking the study medicine. The total time you'd be involved, including screening and the main treatment, would be around 21.5 weeks (or longer if you join the extension study).