Study of the interaction of clobazam with cyclodextrins in solution and in the solid state

Strategies to address low drug solubility in discovery and development

Drugs with low water solubility are predisposed to low and variable oral bioavailability and, therefore, to variability in clinical response. Despite significant efforts to "design in" acceptable developability properties (including aqueous solubility) during lead optimization, approximately 40% of currently marketed compounds and most current drug development candidates remain poorly water-soluble. The fact that so many drug candidates of this type are advanced into development and clinical assessment is testament to an increasingly sophisticated understanding of the approaches that can be taken to promote apparent solubility in the gastrointestinal tract and to support drug exposure after oral administration. Here we provide a detailed commentary on the major challenges to the progression of a poorly water-soluble lead or development candidate and review the approaches and strategies that can be taken to facilitate compound progression. In particular, we address the fundamental principles that underpin the use of strategies, including pH adjustment and salt-form selection, polymorphs, cocrystals, cosolvents, surfactants, cyclodextrins, particle size reduction, amorphous solid dispersions, and lipid-based formulations. In each case, the theoretical basis for utility is described along with a detailed review of recent advances in the field. The article provides an integrated and contemporary discussion of current approaches to solubility and dissolution enhancement but has been deliberately structured as a series of stand-alone sections to allow also directed access to a specific technology (e.g., solid dispersions, lipid-based formulations, or salt forms) where required.

Complexation of celecoxib with beta-cyclodextrin: characterization of the interaction in solution and in solid state

Inclusion complexation between celecoxib, a specific cyclooxygenase II inhibitor, and beta-cyclodextrin (beta-CD) was studied in solution and solid state. Drug cyclodextrin complexes were prepared by spray drying while physical mixtures were obtained by simple blending. Inclusion complexes were characterized by nuclear magnetic resonance spectroscopy (NMR), differential scanning calorimetry (DSC), X-ray diffractometry (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), and polarimetry. Phase solubility analysis was carried out to determine the stability constant. Solubility studies revealed the existence of a 1:1 complex between celecoxib and beta-CD. NMR studies suggested a strong interaction between celecoxib and beta-CD prepared by spray drying. XRD and SEM analysis illustrated that celecoxib existed as an amorphous complexed form in spray-dried complexes. Dissolution studies showed that the celecoxib entrapped in spray-dried complexes dissolved much faster than the uncomplexed drug and physical mixtures. The data obtained suggest that celecoxib forms an inclusion complex with beta-CD in solution and solid state, which was confirmed by various analytical techniques. A shorter t50% of dissolution is found for the formulation prepared by spray drying when compared on a weight basis in a USP II apparatus.

Characterization of physicochemical properties of naproxen systems with amorphous beta-cyclodextrin-epichlorohydrin polymers

Ground mixtures of naproxen with amorphous beta-cyclodextrin-epichlorohydrin soluble (betaCd-EPS) or insoluble cross-linked (betaCd-EPI) polymers were investigated for both solid phase characterization (Differential Scanning Calorimetry, powder X-ray Diffractometry) and dissolution properties (dispersed amount method). The effect of different grinding conditions and of drug-to-carrier ratio was also evaluated. Co-grinding induced a decrease in drug crystallinity to an extent which depended on the grinding time, and was most pronounced for the cross-linked insoluble polymer, particularly in combinations at the lowest drug content. Both cyclodextrin polymers were more effective in improving the naproxen dissolution properties, not only than the parent betaCd but also than hydroxyalkyl-derivatives, and their performance was almost comparable to that of methyl-derivatives, previously found as the best carriers for naproxen. Dissolution efficiencies of naproxen from physical mixtures with betaCd-EPS, thanks to the high water solubility of this Cd-derivative, were up to three times higher than those from the corresponding products with betaCd-EPI. However this difference in their performance became much less evident in co-ground products and tended to progressively diminish with increasing the polymer content in the mixture, according to the better amorphizing power shown by betaCd-EPI during the co-grinding process. The 10/90 (w/w) drug-carrier co-ground products exhibited the best dissolution properties, giving dissolution efficiencies about 30 times higher than that of naproxen alone.

Complexation and solubility behavior of albendazole with some cyclodextrins

The main purpose of this work was to study the albendazole-cyclodextrins complexation equilibrium and to propose a suitable excipient to improve the solubility behavior and dissolution rate of albendazole. The complexation of albendazole with four cyclodextrins, alpha-CD, beta-CD, gamma-CD, and hydroxypropylated (HP)-beta-CD, has been studied by using electronic absorption spectroscopy and molecular mechanics. The equilibrium was studied at pH 7.5 under various temperature conditions, and at pH 1.8 with HP-beta-CD at 298 K. The albendazole binding constant was the greatest for the HP-beta-CD. Both the un-ionized (Alb) and the ionized species (AlbH+) were shown to interact with HP-beta-CD. The studies at different temperatures suggest that the hydrophobic effect is the most important driving force in these systems. Moreover, the dissolution rate studies with beta- and HP-beta-CDs in the buffered aqueous solution at pH 7.5 have been accomplished and the dissolution rate was observed to increase with the cyclodextrin concentration. The solubility behavior was studied with the Higuchi and Connors method. The phase solubility and direct spectroscopy methods reveal a 1:1 inclusion complex in all of the studied cases. Molecular mechanics data show the most probable structure of the complexes.