Failure of valproic acid to inhibit the growth of an ACTH-secreting pituitary adenoma.

Di-n-propylacetic acid (valproic acid) has been reported to lower plasma ACTH concentration after both acute and chronic administration of the drug. To date, there is no report on the efficacy of the drug in inducing regression of ACTH-secreting pituitary adenomas. We report herein our findings in a patient with Nelson's syndrome who was treated with valproic acid for over a year. Despite a lowering of her plasma ACTH concentration during therapy with valproic acid, the patient's tumour showed no evidence of regression while she was taking the drug. In view of these findings, valproic acid therapy for ACTH-secreting pituitary tumours needs to be re-evaluated.