Hyponatraemia associated with lamotrigine in cranial diabetes insipidus.

We report the cases of two children with cranial diabetes insipidus who were treated with lamotrigine for seizures and who had accompanying changes in desmopressin requirements. Lamotrigine is a new anticonvulsant chemically unrelated to other existing antiepileptic drugs. Studies suggest it acts at voltage-sensitive sodium channels and also decreases calcium conductance. Both of these mechanisms of action are shared by carbamazepine, which can cause hyponatraemia secondary to inappropriate secretion of antidiuretic hormone. It is possible that the effect of lamotrigine on fluid balance in the cases described is also centrally mediated.