Hyperinsulinemia associated with normal C-peptide levels in a woman treated with isoniazide

The authors report on the observation of a woman treated with isoniazide, who presented clinical symptoms of hypoglycemia during treatment (seating, confusion, anxio-depressive syndrome, lipothymia). After the antitubercular treatment was stopped, a moderate hypoglycemia without clinical manifestations accompanied by a marked hyperinsulinemia and normal C-peptide values was detected during a Conn's test. Serum gel filtration on Sephadex G 50 Fine showed that the measured hyperinsulinemia was effectively due to an insulin excess. This excess did not seem caused by surreptitious insulin injection. This seems to be the consequence of a deficiency in insulin catabolism because the C-peptide level was normal. The possible role of isoniazide on carbohydrate metabolism is discussed.