Urolithiasis in patients on high dose felbamate

We report 4 cases of felbamate urolithiasis. We identified only 1 prior case report of a felbamate stone. Felbamate is an antiepileptic drug used to treat refractory seizures and has minor side effects when given in recommended doses. We analyzed the characteristics, evaluation, treatment and outcomes in this challenging group of patients.

Following institutional review board approval, we conducted a retrospective chart review of all patients who presented with a diagnosis of urolithiasis, were on felbamate and had stone analysis consistent with a felbamate origin.

All 4 patients had refractory seizures and 3 had severe developmental delay. Presentation ranged from an incidental finding to gross hematuria to agitation and pain. Stones were not visible on plain x-ray except in 1 case involving mixed stone composition. Decrease or cessation of the drug has not been feasible in 2 patients, and 3 patients have had recurrent stones. Initial stone analysis did not correctly identify the stone composition as felbamate in 2 cases, suggesting that the origin of these stones may not always be recognized.

We report the occurrence of felbamate stones in a series of patients on high dose felbamate therapy. Accurate diagnosis is made more difficult by the clinical complexity of the patient population (including severe developmental delay), the radiolucent nature of the stones and the possibility of inaccurate analysis of stone composition.