Measurement of human brain dexfenfluramine concentration by 19F magnetic resonance spectroscopy

Objective: The goals of this study were to quantitate the brain concentrati on of the anorectic drug dexfenfluramine (DF) in human subjects receiving c linical doses of DF and to determine whether human brain DF concentrations approach those reported to cause irreversible neurochemical changes in anim als. Each subject's brain DF concentration was measured several times over an extended period of DF treatment to determine whether drug accumulation i n the brain would plateau or continue to increase throughout the treatment period. Design: Fluorine magnetic resonance spectroscopy (19F-MRS) was used to directly detect and quantitate brain levels of the fluorinated drug dex fenfluramine and its active metabolite dex-norfenfluramine (dNF). Patients received 15 mg dexfenfluramine BID for 90 days. 19F-MRS measurements were p erformed at baseline and at three times during the treatment period. Partic ipants: Twelve women (age 38-54 years) who were obese, with body mass indic es of 28.4-37.4, but otherwise healthy. Results: The combined concentration of DF and nDF reached steady-state in the human brain after approximately 10 days of treatment. The steady-state brain concentration averaged approxi mately 4 mu M and did not tend to increase significantly during the 90 day treatment period. Conclusions: These results demonstrate that fluorinated d rugs can be quantified using 19F MRS at concentrations below 10 mu M in the human brain. The time-course data suggest that brain DF concentrations par allel DF plasma pharmacokinetics in humans. Measured brain dexfenfluramine/ nor-dexfenfluramine concentrations were well below levels previously found to cause irreversible brain alterations in animals. (C) 1999 Elsevier Scien ce B.V. All rights reserved.