Fenfluramine treatment of autism: relationship of treatment response to blood levels of fenfluramine and norfenfluramine.

Nine children meeting DSM-III criteria for infantile autism were treated with fenfluramine hydrochloride or inactive placebo in a double-blind crossover trial that followed the protocol for the fenfluramine multicenter study. Parents of the two children who had had the highest fenfluramine blood levels wished to have their children continue on fenfluramine, although the improvement they saw could not be demonstrated on the various rating instruments employed. The results of the study, while providing minimal support in themselves for the effectiveness of fenfluramine, do raise the possibility that fenfluramine blood levels might be related to treatment response.