In Vitro Investigation of the Effect of Ambient Humidity on Regional Delivered Dose with Solution and Suspension MDIs

Background: Existing literature has shown that high relative humidity (RH) affects in vitro aerosol drug delivery of nebulizer and pressurized metered dose inhaler (pMDI) formulations. The aim of this study is to investigate in vitro mouth-throat deposition and lung delivery of selected solution and suspension pMDI formulations, under a range of RH, temperature, and flow rate conditions. Methods: The Alberta Idealized Throat was connected to a collection filter and placed in an environmental control chamber. The formulations selected were beclomethasone dipropionate (BDP) in 13% w/w ethanol/1.3% w/w glycerol and HFA-134a propellant solution (BDP HFA134a), BDP in 13% w/w ethanol and HFA-227 propellant solution (BDP HFA227), and Flixotide Evohaler (fluticasone propionate 250 mu g/dose in HFA-134a suspension). Each of these pMDI formulations was dispersed into the mouth-throat and filter assembly in triplicate, according to an experimental matrix consisting of the following conditions: air flow rates of 28.3, 60, and 90 L/min; 0%, 35%, and 80% RH; operating temperatures of 20 degrees C and 40 degrees C. Results: There was a general increase in mouth-throat deposition and corresponding decrease in filter deposition (representing lung dose fraction), with increasing RH for both BDP HFA134a and Flixotide pMDIs. Increasing temperature from 20 degrees C to 40 degrees C resulted in decreased mouth-throat deposition and increased lung dose fraction for the solution pMDIs, but generally no effect for the suspension pMDI. Conclusions: Not only is the dose delivery of pMDI formulations affected by environmental conditions (in some cases causing up to 50% reduction in lung delivery), but solution and suspension formulations also behave differently in response to these conditions. These results have implications during dosage form design, testing, and for usage patient use.