Epilepsy drug. Box of Sabril sachets for the treatment of epilepsy. Each sachet contains 500 milligrams of powdered vigabatrin to be dissolved in water. Epileptic seizures are caused by uncontrolled and excessive electrical activity in the brain. This drug prevents seizures by increasing the amount of the inhibitory neurotransmitter GABA (gamma-aminobutyric acid) in the brain.