RESUMEN
Aims: Among the antiepileptic drugs (AEDs) applied for secondary prophylaxis of posttraumatic epilepsy (PTE), carbamazepine (CBZ) may cause severe side effects and worsen traumatic brain injury (TBI). Presentation of Case: Two days after a bicycle accident causing severe TBI, a 23yo female developed a questionable seizure and received CBZ. Since then she required substitution of sodium. Six days after the accident she was extubated. Serum sodium was 123mmol/l. One day after transfer to the general ward, she was found comatose with a serum sodium of 114mmol/l. Cerebral CT showed diffuse cerebral edema. Electroencephalography did not record paroxysmal activity. After replacement of CBZ by levetiracetam, her condition markedly improved with a favourable outcome. Discussion and Conclusion: CBZ was made responsible for severe hyponatraemia in the presented case after exclusion of all other possible causes. Hyponatraemia may trigger the recurrence of cerebral edema after TBI. Hyponatraemia from CBZ may favourably respond to slow substitution of sodium with physiologic saline. CBZ for secondary prophylaxis of PTE may cause hyponatraemia, cerebral edema, and deterioration of pre-existing TBI. Replacement of CBZ by levetiracetame may resolve the condition. CBZ should be used with caution for secondary prophylaxis of PTE in TBI.