Hi Rama S V,
has been prescribed in an attempt to prevent occurrence of seizures. It is not uncommon for this medication to be prescribed after neurosurgical operations. However, there is usually not an increased incidence of seizures following evacuation of chronic subdural haematoma
. As far as your question regarding the duration of taking this medicine goes, there is no hard and fast rule and practices vary from giving it for a week or two to much longer periods. This is according to the preference of the treating physician and practices vary.
Hope this helps.