A fast and sensitive UHPLC–MS/MS method for the determination of N‐butylscopolamine in human plasma: application in a bioequivalence study

We have developed and validated a fast and sensitive ultra high-performance liquid chromatography with positive ion electrospray ionization tandem mass spectrometry (UHPLC-ESI-MS/MS) method for determining N-butylscopolamine levels in human plasma using propranolol as an internal standard (IS). The acquisition was set up in the multiple reaction monitoring (MRM) mode with the transitions m/z 360.2 → 138.0 for N-butylscopolamine and m/z 260.2 → 116.1 for IS. This method uses a liquid-liquid extraction process with dichloromethane. The analyte and IS were chromatographed on a C18 – 50 x 2.1 mm, 1.7-µm column through isocratic elution with acetonitrile:5-mM ammonium acetate (adjusted to pH 3.0 with formic acid). The method was linear in the 1 to 1000 pg/mL range for N-butylscopolamine and was selective, precise, accurate, and robust. The validated method was successfully applied to perform a bioequivalence study of the reference (Buscopan®, from Boehringer Ingelheim) and the test sample coated-tablet formulations (from Foundation for Popular Remedy [FURP]), both containing 10 mg of N-butylscopolamine bromide administered as a single dose. Using 58 healthy volunteers and accounting for the high intra-individual variability confirmed by statistical calculations (38%), the two formulations were considered bioequivalent because the rate and extent of absorption (within 80–125% interval), satisfying international requirements.