[Nephrolithiasis and topiramate]

Topiramate (TPM) is a new antiepileptic drug whose multiple mechanisms of action justify both its broad therapeutic spectrum and its increasingly widespread use in childhood epilepsy. TPM acts as a carbonic anhydrase inhibitor and, although this does not affect its effectiveness as an antiepileptic, it does account for certain side effects such as nephrolithiasis. The frequency of nephrolithiasis secondary to TPM in childhood is unknown and we have only found reports of five cases in children.

We describe two cases of medication-resistant infantile epilepsy--a 3-year-old female with Dravet's syndrome and a male aged 4.5 years with Lennox-Gastaut syndrome. In both cases the decision was made to introduce TPM as add-on therapy after a prolonged therapeutic programme; a high degree of effectiveness was achieved in both patients. Nevertheless, the two patients developed nephrolithiasis secondary to TPM, which in the second case was related to the simultaneous treatment with adrenocorticotropic hormone (ACTH), while no known favouring factor was found in the first patient.

We outline the physiopathogenic mechanism explaining nephrolithiasis secondary to TPM, the risk factors involved and the therapeutic and preventive options available in dealing with this side effect, which occurs in a low percentage of cases but which usually means stopping administration of this therapy. We therefore believe it necessary to analyse the risk factors for nephrolithiasis before prescribing the drug and we suggest that generalised preventive measures should be implemented, especially in children who are carriers of encephalopathies or conditions that reduce mobility.