title: Osmotic properties of sulfobutylether and hydroxypropyl cyclodextrins.
abstract: OBJECTIVE
  The purpose of this study was to determine the osmolality of sulfobutylether (SBE) and hydroxypropyl (HP) derivatives of cyclodextrins (CDs) via vapor pressure osmometry (VPO) and freezing point depression (FPD). (SBE) and HP-CDs are efficient excipients capable of solubilizing and stabilizing poorly water-soluble drugs in parenteral formulations. (SBE)-CDs have also been used as solubility enhancers and osmotic agents for the sustained release of poorly water-soluble drugs from osmotic pump tablets. The knowledge of the CD's osmolality in solution or inside such tablets would allow one to further characterize the release mechanisms.
  
  
  METHODS
  Experiments were conducted at 37 degrees C with eight types of HP and (SBE)-CDs. The aqueous solutions ranged from 0.005-0.350 mol(-1). Methods were developed to allow the measurement of high osmolalities using a vapor pressure osmometer or a differential scanning calorimeter.
  
  
  RESULTS
  The osmolality calculations from the VPO and FPD measurements correlated well. The osmolality of (SBE)-CDs was significantly higher than the osmolality of HP-CDs and increased with the total degree of substitution (TDS). All CDs showed deviations from ideality at high concentrations.
  
  
  CONCLUSIONS
  Empirical correlations of osmolality with concentration and TDS allowed the prediction of osmolality over a wide concentration range. This study also gave some useful insights into the behavior of CD derivatives in solution.
authors.affiliation: Department of Pharmaceutical Chemistry, The University of Kansas, Lawrence 66047, USA.
authors.forename: E A
authors.initials: EA
authors.lastname: Zannou
authors.forename: W H
authors.initials: WH
authors.lastname: Streng
authors.forename: V J
authors.initials: VJ
authors.lastname: Stella
mesh_terms: D000073738:2-Hydroxypropyl-beta-cyclodextrin; D002152:Calorimetry, Differential Scanning; D003505:Cyclodextrins / Q000737:chemistry*; D004987:Ethers / Q000737:chemistry*; D005615:Freezing; D009994:Osmolar Concentration; D009995:Osmosis; D013607:Tablets; D014867:Water / Q000737:chemistry; D047392:beta-Cyclodextrins
chemical_list: D003505:Cyclodextrins; D004987:Ethers; D013607:Tablets; D047392:beta-Cyclodextrins; D014867:Water; D000073738:2-Hydroxypropyl-beta-cyclodextrin; C093196:SBE4-beta-cyclodextrin