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

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journal

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Original languageEnglish
Pages (from-to)1104-1109
Journal / PublicationPharmaceutical Research
Issue number9
Publication statusPublished - 2000
Externally publishedYes


Purpose. To use a single particle levitation technique to investigate the equilibrium water sorption characteristics in both the evaporation and growth of four respiratory drugs at 37°C: atropine sulfate (AS), isoproterenol hydrochloride (IPHC) and isoproterenol hemisulfate (IPHS) and disodium cromoglycate (DSCG). Methods. The equilibrium water content was measured as a function of relative humidity (RH) by a single particle levitation technique using an electrodynamic balance (EDB). The change of water content was determined by the voltage required to balance the weight of the levitated particle electrostatically. The water activities of bulk samples were also measured. Growth ratios were determined and compared with values in the literature. Results. Crystallization or deliquescence was not observed for AS, IPHC and LPHS. The hysteresis in the water cycle was not observed for any of the drugs. At RH - 0%, AS particles still contain about 5% water but IPHC and IPHS particles do not contain any residual water. The aerodynamic growth ratio from RH 0% to 99.5% is 2.60, 2.86, 2.42 and 1.26 for AS, IPHC, IPHS and DSCG, respectively. Supersaturated droplets of IPHC and IPHS are expected 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 may experience supersaturation before they enter the human body and this could exert a significant influence both on particle loss before inhalation and on the deposition of the drugs in the lungs. The EDB is a convenient and reliable tool for studying the hygroscopic properties of pharmaceutical aerosols, especially for supersaturated solutions.

Research Area(s)

  • Atropine sulfate, Disodium cromoglycate, Hygroscopic property, Isoproterenol hemisulfate, Isoproterenol hydrochloride, Particle growth, Water activity