Modulation of release rate and barrier transport of Diclofenac incorporated in hydrophilic matrices: Role of cyclodextrins and implications in oral drug delivery

The aim of this work was to investigate how the incorporation of a hydrophilic cyclodextrin (CD) inside erodible hydrophilic matrices affects drug-release behavior and transport properties through artificial and biological membranes. To this purpose, Diclofenac (Dic) was incorporated in poly(ethyleneoxide) (PEO) matrices as poorly soluble free acid (DicH) or freely water-soluble sodium salt (DicNa) in the presence or absence of hydroxypropyl-β-cyclodextrin (HPβCD). Preliminary experiments demonstrated that HPβCD increased Dic apparent solubility as a function of its amount in the solution and medium pH due to complex formation. Permeation of ionized Dic through porcine buccal mucosa gave higher values of JSS and Kp as compared to silicon membranes and depended on the presence of HPβCD. Incorporation of HPβCD in PEO tablets resulted in an increase of release rate for both forms of Dic whereas cumulative drug flux through silicon membranes and porcine buccal mucosa was increased for DicH and decreased for DicNa. An interpretation of this behavior was attempted on the basis of the presence of a transport resistance occurring inside the hydrated gel matrix as modified by the presence of CD. In conclusion, this study has demonstrated that the use of CDs in hydrophilic matrices intended for oral drug delivery should be rationalized since their modulator effect relies not only on drug-dissolution rate but also on environment where drug release occurs (aqueous medium, membrane interface).