The minimal metabolism of inhaled 1,1,1,2-tetrafluoroethane to trifluoroacetic acid in man as determined by high sensitivity 19F nuclear magnetic resonance spectroscopy of urine samples.

Abstract

In this work, oxidative metabolism of the new propellant, 1,1,1,2-tetrafluoroethane to trifluoroacetic acid in man is shown to be minimal. Alternative propellants and refrigerants are under development to replace the currently used chlorofluorocarbons which lead to stratospheric ozone depletion. One potentially useful replacement is the hydrofluorocarbon, 1,1,1,2-tetrafluoroethane (HFA-134a). Before it can be used, however, particularly as a propellant in an aerosol pharmaceutical formulation whereby the compound is in effect dosed to people, it is important that the safety of this compound is established. As a part of this safety evaluation it is necessary to understand the metabolism of HFA-134a. In this work the production of the potential oxidative metabolite of HFA-134a, trifluoroacetic acid (TFA) has been studied in human urine following inhalation dosing with HFA-134a. The concentrations of TFA in urine have been measured using a highly sensitive 19F nuclear magnetic resonance procedure with a limit of detection of 10 ng ml-1 based on an acquisition time of only 2.25 h per sample. TFA is the only fluorinated species observed in the urine samples and only at very low levels, indicating that the oxidative route of metabolism can occur in vivo in man, but this metabolism is minimal in terms of percentage of administered dose.