 Crossover design for subjects with treatment failure. If subjects condition deteriorates after randomization to lamotrigine or valporate, subject will be crossed over to the other arm of the study, i.e. those who failed sodium valproate will be treated with lamotrigine and vise versa and vise versa. Subjects who will have failed the crossover switch will be removed from the study. Deterioration will be defined as a three-point worsening in the patients YMRS score lasting more than 72 hours. 