Development and Validation of RP-HPLC Method for Simultaneous Estimation of Tiotropium Bromide, Formoterol Fumarate, and Olodaterol HCl in Bulk and Metered Dose Aerosols: Application to Olodaterol HCl Forced Degradation Study and Degradation Kinetics

Tiotropium bromide monohydrate (TTP) is coformulated with either formoterol fumarate dihydrate (FMR) or olodaterol HCl (ODT) in metered dose inhalations for treatment of asthma. So, a simple and selective reversed-phase liquid chromatographic method was developed and validated for simultaneous determination of TTP, FMR, and ODT in bulk and metered dose aerosols. The method was based on isocratic elution on a reversed-phase Eurospher II C18 column (250 mm x 4.6 mm, 5 A mu m) with 20 mM anhydrous KH2PO4 (containing 0.2% triethylamine, v/v, pH adjusted to 6 with orthophosphoric acid):methanol (55:45, v/v) as mobile phase at flow rate of 1 mL min(-1). The proposed method was utilized for a forced degradation study of ODT on exposure to acid, alkali, oxidation, thermal, and photostress conditions. Eleven newly isolated ODT degradation products were characterized and verified chemically by using liquid chromatography/tandem mass spectrometry (LC-MS/MS). Moreover, the kinetics of alkaline degradation of ODT was investigated. An Arrhenius plot was constructed, and the apparent first-order rate constant, half-life time, shelf-life time, and activation energy of the degradation process were calculated.