Flutamide - Hydroxypropyl-beta-cyclodextrin complex: Formulation, physicalcharacterization, and absorption studies using the Caco-2 in vitro model

The objective of this research was to formulate flutamide (FLT) in hydroxyp ropyl-beta-cyclodextrin (HP beta CyD), and to investigate FLT transcellular permeation from the complex using the Caco-2 monolayer in vitro model. Met hods: Classical solubility data were used to derive thermodynamic parameter s which, together with Differential Scanning Calorimetry (DSC), H-1-NMR and F-19-NMR, were used to characterize and derive stability constants for the FLT-HP beta CyD complex. The Caco-2 cell line was used to examine the role of HP beta CyD on the passage of FLT across cell monolayers in vitro. Resu lts: The solubility of FLT in water (1.46 mmol/L) increased almost 170 time s (to 243.45 mmol/L) in the presence of 50% (w/v) HP beta CyD. Solubility d ata for FLT in aqueous HP beta CyD were used to derive thermodynamic parame ters (Delta G degrees at 298 K = -3.48, Delta H degrees = 2.85, Delta S deg rees at 298 K = 21.24). The solubility of FLT in HP beta CyD increased prop ortionally with an increase in temperature. The FLT-HP beta CyD complex had an A(L)-type (DSC) isotherm, consistent with a linear increase in FLT solu bility and unchanged stoichiometry. The DSC of free FLT and HP beta CyD sho wed endothermic peaks at 110 degrees C and 300 degrees C, respectively. FLT -HP beta CyD did not display a free-FLT endothermic response, but exhibited broadening of the endothermic peak in the HP beta CyD region. F-19- and H- 1-NMR chemical shifts moved upfield as a function of its increased solubili ty in the presence of HP beta CyD. The FLT-HP beta CyD stability constant, K-s (1:1) was estimated to be 356 M-1 and 357 M-1, from thermodynamic and F -19 NMR data, respectively. The apical-to-basal permeability coefficient (P -eff = 4.75x10(-5) cm.s(-1)) for FLT across Caco-2 cell monolayers at 37 de grees C increased as HP beta CyD concentrations were reduced, indicative of transepithelial passage via passive diffusion of available free FLT in sol ution. Studies in the presence and absence of Ca2+ ruled out a significant paracellular transport component. Conclusions: FLT-HP beta CyD is a relativ ely stable, 1:1 inclusion complex. Formation of this complex substantially increases the water solubility of FLT, but HP beta CyD, except in high dilu tion, reduces transcellular passage of FLT in the Caco-2 cell in vitro mode l.