Poly(lactide-co-glycolide)/cyclodextrin (polyethyleneimine) microspheres for controlled delivery of dexamethasone

Water-in-oil-in-water (w1/o/w2) solvent evaporation method is a technique for encapsulation and protection of water soluble and chemically sensitive bioactive molecules.One of the most important disadvantages of this method is the diffusion of bioactive molecule, during synthesis, from the primary to the secondary aqueous phase, reducing dramatically the encapsulation yield. Therefore, dexamethasone sodium phosphate (DM), a corticosteroid water soluble drug, which is sensitive to degradation, was first complexed with hydroxypropyl cyclodextrin (HPCD), γ-cyclodextrin (γ-CD) or polyethyleneimine (PEI) and then entrapped in poly(lactic-co-glycolic acid) (PLGA) microspheres obtained by w1/o/w2 solvent evaporation method. Association equilibrium constants for the formation of the HPCD/DM and γ-CD/DM inclusion complexes were also calculated, being 1.420 × 103 M− 1 and 1.447 × 104 M− 1, respectively. PEI was proved to be the most efficient DM trapper, retaining the highest amount of the drug in microspheres, followed by γ-CD and HPCD. Despite the high values of the association equilibrium constants for DM binding to HPCD and γ-CD, both cyclodextrins are not able to protect the drug against UV irradiation. The morphology of the microspheres as well as the drug entrapment efficiency and the release rates are influenced by complexing agents and the ratio between the primary aqueous phase and the organic phase.