Quantification of betamethasone in human plasma by liquid chromatography-tandem mass spectrometry using atmospheric pressure photoionization in negative mode

Betamethasone was extracted from 0.5 ml human plasma by liquid-liquid extraction (LLE) using chloramphenicol as internal standard. The method has a chromatographic run of 2.5 min using a C18 analytical column (100 mm × 2.1 mm i.d.) and the linear calibration curve over the range was linear from 0.05 to 50 ng ml−1 (r2 > 0.993). The between-run precision, based on the relative standard deviation replicate quality controls was 94.1% (0.15 ng ml−1), 90.7% (4.0 ng ml−1) and 97.2% (40 ng ml−1). The between-run accuracy for the above-mentioned concentrations was 11.9, 9.0 and 9.8%, respectively. The method herein described was employed in a bioequivalence study of two formulations of dexchlorpheniramine/betamethasone 2 mg/0.25 mg tablets.