title: In-vitro prediction of bioavailability following extravascular injection of poorly soluble drugs: an insight into clinical failure and the role of delivery systems.
abstract: OBJECTIVE
  To investigate the feasibility of using an in-vitro model to simulate the incidence of post-injection drug precipitation (PDP), and to identify the roles of drug properties and delivery systems in its occurrence.
  
  
  METHODS
  A literature review on incomplete absorption following extravascular injection (subcutaneous and intramuscular) was conducted. Six model drugs in nine different formulations were studied for an in-vitro/in-vivo correlation. A rapid in-vitro dilution method using a 96-well plate was used for predicting PDP by dilution with a physiological buffer. New formulations based on hydroxypropyl-β-cyclodextrin (CD), with and without co-solvents or pH control, were developed and tested on the in-vitro model.
  
  
  RESULTS
  The occurrence of precipitation detected from the in-vitro dilution model appeared to be correlated with clinical reports and animal studies. The formulation components played an important role in determining the potential for drug precipitation on dilution or pH neutralization. CD was found to reduce the tendency for precipitation. The addition of co-solvents may reduce the effect of CD, depending on the solvent used.
  
  
  CONCLUSIONS
  The in-vitro model can be used as a cost-effective screening tool in injectable formulation development for safe and effective delivery of poorly soluble drugs. PDP can be circumvented with a well-designed formulation.
authors.affiliation: School of Pharmacy, The University of Auckland, Auckland, New Zealand.
authors.forename: Zimei
authors.initials: Z
authors.lastname: Wu
authors.forename: Dalia
authors.initials: D
authors.lastname: Hassan
authors.forename: John P
authors.initials: JP
authors.lastname: Shaw
mesh_terms: D000042:Absorption; D000818:Animals; D001682:Biological Availability; D011232:Chemical Precipitation; D002626:Chemistry, Pharmaceutical; D003198:Computer Simulation; D016503:Drug Delivery Systems / Q000379:methods*; D006801:Humans; D007201:Indicator Dilution Techniques; D007273:Injections, Intramuscular; D007279:Injections, Subcutaneous; D007700:Kinetics; D008954:Models, Biological; D004364:Pharmaceutical Preparations / Q000008:administration & dosage / Q000737:chemistry; D011237:Predictive Value of Tests; D012995:Solubility; D017211:Treatment Failure
chemical_list: D004364:Pharmaceutical Preparations
keywords: bioavailability of extravascular injection; cyclodextrins; in-vitro prediction; poorly soluble drugs; post-injection drug precipitation