The physico-chemical properties of salmeterol and fluticasone propionate in different solvent environments

Tho physico-chemical properties of two anti-asthmatic drugs, salmeterol xin afoate and fluticasone propionate, have been studied in both aqueous and no n-aqueous solvent environments. Ultraviolet-visible (UV-Vis) spectroscopy, fluorescence spectroscopy and electrospray ionisation mass spectrometry (ES I-MS) have been used to characterise the interaction of the drugs in 70:30 (v/v) methanol/water solutions. First derivative UV-Vis spectra measurement s indicate that an interaction takes place between the two drugs in a binar y solvent system. Fluorescence studies indicate that an increase in the con centration of fluticasone propionate results in a decrease in the fluoresce nce signal of the salmeterol for mixed solutions of the drugs. Analysis of a mixture of the two drug solutions using mass spectrometry also shows evid ence of salmeterol-fluticasone propionate interaction and dimer formation w ith respect to both the salmeterol and the fluticasone propionate. Model me tered dose inhalers (MDI) of both individual samples and mixtures of the dr ugs were formulated as suspensions ill solvent CFC-113. The extent of depos ition onto different inhaler components, such as the aluminium alloy canist er, Teflon coated canister and the metering valve was evaluated by high-per formance liquid chromatography (HPLC) of the methanol/water washings of the deposited drug(s), Changing the nature of the surface properties of the co ntainer resulted in a significant difference in the extent of deposition. T he deposition of the individual drugs was found to increase as the dispersi on concentration of the drug increases. However, the formulation based on a combination of the two drugs was found to show different deposition behavi our compared to the individual drug formulations. The deposition of the dru gs, onto the aluminium alloy canister and the metering valve, decreases as the combined dispersion concentration of the two drug increases. (C) 2000 E lsevier Science B.V. All rights reserved.