TESTING OF DRY POWDER AEROSOL FORMULATIONS IN DIFFERENT ENVIRONMENTAL-CONDITIONS

Dry powder aerosol performance of albuterol and albuterol sulfate from a model dry powder inhaler (DPI) was studied under varying environmen tal conditions using a twin stage impinger (TSI). Pure micronized drug was metered into the DPI and the loaded inhaler inserted into the inl et of the TSI housed in a pre-equilibrated environmental chamber. Afte r 3 min, the drug was aerosolized at 60 1/min for 20 s. Washings from the DPI and TSI were analyzed by UV spectroscopy. Temperature and rela tive humidity (RH) were varied (20, 30 and 45 degrees C; 30-95% RH). D rug collected in stage 2 of the TSI was expressed as fine particle dos e or fine particle percent of either the loaded dose or the amount emi tted from the mouthpiece of the DPI. These values decreased with incre asing relative humidity for both albuterol and albuterol sulfate at an y given temperature with differences being more marked at higher tempe ratures. For example, at 30 degrees C, the mean(experimental range) fi ne particle percent of the emitted dose of albuterol sulfate was 59.4( 3.1) and 35.8(5.7)% at 43 and 85% RH, respectively, n = 3 (p < 0.05). Increasing temperature also resulted in diminished aerosol performance . These differences were more marked for albuterol sulfate. The fine p article percent of the emitted dose of albuterol base was always great er than that of albuterol sulfate under similar environmental conditio ns. The reverse was true when fine particle percents of the loaded dos e were considered because only 32 +/- 6.6% of the loaded albuterol was emitted from the inhaler as compared to 58.5 +/- 6.3% of albuterol su lfate (mean +/- SD, n = 27). There is a need, in some circumstances, t o define specific ranges of temperature and humidity for the testing o f dry powder aerosols.