Study of the hygroscopic properties of selected pharmaceutical aerosols using single particle levitation

Purpose. To use a single particle levitation technique to investigate the e quilibrium water sorption characteristics in both the evaporation and growt h of four respiratory drugs at 37 degreesC: atropine sulfate (AS), isoprote renol hydrochloride (IPHC) and isoproterenol hemisulfate (IPHS) and disodiu m cromoglycate (DSCG). Methods. The equilibrium water content was measured as a function of relati ve humidity (RH) by a single particle levitation technique using an electro dynamic balance (EDB). The change of water content was determined by the vo ltage required to balance the weight of the levitated particle electrostati cally. The water activities of bulk samples were also measured. Growth rati os were determined and compared with values in the literature. Results Crystallization or deliquescence was not observed for AS, IPHC and IPHS. The hysteresis in the water cycle was not observed for any of the dru gs. At RH similar to 0%, AS particles still contain about 5% water but IPHC and IPHS particles do not contain any residual water. The aerodynamic grow th ratio from RH 0% to 99.5% is 2.60, 2.86, 2.42 and 1.26 for AS, IPHC, IPH S and DSCG, respectively. Supersaturated droplets of IPHC and IPHS are expe cted to exist in the ambient conditions. DSCG is in a solid state in the RH range of 10-90%. Conclusions. It is expected that some aerosolized drugs of low solubility m ay experience supersaturation before they enter the human body and this cou ld exert a significant influence both on particle loss before inhalation an d on the deposition of the drugs in the lungs. The EDB is a convenient and reliable tool for studying the hygroscopic properties of pharmaceutical aer osols, especially for supersaturated solutions.