<prompt> A patient who is being treated for temporal lobe epilepsy complex paial seizures and who is having recurrent seizures on his chronic regimen of carbamazepine is given phenobarbital as a second drug. However, the seizures increase in frequency. What is the probable reason for the apparent deleterious effect of adding phenobarbital:Intracerebral bleeding from worsening bone marrow suppressionDecreased carbamazepine levelDecreased stability of CNS neuronal membranesHypokalemia  <response>: Answer is B Decreased Carbamazepine levels: Phenobarbitone is a microsomal enzyme inducer so administration of phenobarbitone induces the metabolism of carbamazepine and reduces its level in blood. 