 In phase 2 of the project the second-line drug will be given in monotherapy. This means that valproate will be withdrawn. The dose of the second drug will be increased accordingly. The effectiveness of the drugs in monotherapy will be evaluated. The combined results of phase 1 and 2 will enable us to interpret the results. When all patients who became seizure free on a combination in phase 1, stay seizure free in phase 2, the efficacy of the combination should be attributed to the add-on drug. When these patients all develop seizures again, the efficacy of the combination should be attributed to the combination. 