[Generic carbamazepine-induced subacute adrenal insufficiency?]

Iatrogenic causes of adrenal insufficiency in Addison's disease are exceptional. We report the case of a patient with a history of epilepsy (taking carbamazepine, Tégrétol LP) and Addison's disease (treated by hydrocortisone (HDC) 30 mg/d, Dectancyl 0,5 mg/d, Florinef 50 mg/d). Recent digestive disorders required emergency hospitalization. The physical examination was normal and laboratory tests showed hyponatremia, hyperkalemia, and elevated serum ACTH. The course was rapidly favorable after rehydration and up-titration of the drug regimen. No triggering factor was identified, but the Tégrétol LP had been replaced for 3 months by a generic drug with the same quantity of active ingredients and the same bioavailability, but with a different excipient (the generic drug was not encapsulated). Could these differences have increased the serum level of carbamazepine and lead to more rapide HDC metabolism by enzymatic induction? Could poorer digestive tolerance have decreased HDC absorption? The hypothesis of carbamazepine overdosage is unlikely because the assay remained within the therapeutic range and hyperkaliemia would favor adrenal decompensation. In conclusion, this single case cannot prove drug interaction but does point out the importance of being prudent when modifying a well--tolerated regimen in a patient with Addison's disease.