Identification of benzoylcarnitine in the urine of a patient of hyperammonemia.

Benzoylcarnitine was identified in the urine of a patient with a carbamoyl-phosphate synthase I deficiency for whom sodium benzoate and L-carnitine had been used to treat hyperammonemia. This is a newly identified metabolite of benzoate. Its excretion in the urine was increased day by day at the administration of both sodium benzoate and L-carnitine from 0.10 to 2.25 mmol/g creatinine. Since there is the possibility of a secondary carnitine deficiency and an increase of benzoyl toxicity after long-term therapy with benzoate supplementation and protein restriction, it is important to monitor the urinary excretion of benzoylcarnitine.