Determination of bambuterol, a prodrug of terbutaline, in plasma and urine by gas chromatography/mass spectrometry.

(R,S)-Bambuterol was isolated from plasma and urine by solid-phase extraction and analysed as its trimethylsilyl derivative by gas chromatography/chemical ionization mass spectrometry with ammonia as the reagent gas. Deuterium-labelled bambuterol was used as internal standard. An esterase inhibitor was added to plasma to prevent hydrolysis of bambuterol in the plasma sample. Bambuterol could be measured in plasma down to 1 nmol l-1 with a within-day variation of less than 5% (coefficient of variation). The lower limit of measurement in urine was judged to be 8 nmol l-1, a concentration at which the within-day variation was 5.4% (coefficient of variation).