Eudragits are amorphous polymers having glass transition temperatures between 9 to > 150(o)C. Eudragits are non-biodegradable, nonabsorbable, and nontoxic. Anionic Eudragit L dissolves at pH > 6 and is used for enteric coating, while Eudragit S, soluble at pH > 7 is used for colon targeting. Studies in human volunteers have confirmed that pH drops from 7.0 at terminal ileum to 6.0 at ascending colon, and Eudragit S based systems sometimes fail to release the drug. To overcome the shortcoming, combination of Eudragit S and Eudragit L which ensures drug release at pH < 7 has been advocated. Eudragit RL and RS, having quaternary ammonium groups, are water insoluble, but swellable/permeable polymers which are suitable for the sustained release film coating applications. Cationic Eudragit E, insoluble at pH ≥ 5, can prevent drug release in saliva and finds application in taste masking.

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Our objective is to mechanistically understand the implications of processing-induced lattice disorder on the stability of pharmaceutical cocrystals. Caffeine−oxalic acid (CAFOXA) and dicalcium phosphate anhydrate (DCPA) were the model cocrystal (drug) and excipient, respectively. Cocrystal−excipient mixtures were milled for short times (≤2 min) and stored at room temperature (RT)/75% RH. Milling-induced lattice disorder was quantified using powder X-ray diffractometry and gravimetric water sorption. Milling for even 10 s resulted in measurable disorder and an attendant tendency of the solid to sorb water. This was followed by cocrystal−excipient interaction leading to dissociation. The proposed mechanism of cocrystal dissociation entails the following sequence: sorption of water by disordered regions, dissolution of CAFOXA and DCPA in the sorbed water, followed by proton transfer from the coformer (oxalic acid) to DCPA, and the formation of hydrates of caffeine and calcium oxalate. As such, CAFOXA is a robust cocrystal, stable even under elevated humidity conditions (RT/98% RH). However, in a drug product environment, routine pharmaceutical processing steps such as milling and compaction have the potential to induce sufficient disorder to render it unstable.

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Abstract. Drug-polymer miscibility is one of the fundamental prerequisite for the successful design and development of amorphous solid dispersion formulation. The purpose of the present work is to provide an example of the theoretical estimation of drug-polymer miscibility and solubility on the basis of FloryHuggins (F-H) theory and experimental validation of the phase diagram. The F-H interaction parameter, χ d-p , of model system, aceclofenac and Soluplus, was estimated by two methods: by melting point depression of drug in presence of different polymer fractions and by Hildebrand and Scott solubility parameter calculations. The simplified relationship between the F-H interaction parameter and temperature was established. This enabled us to generate free energy of mixing (ΔG mix ) curves for varying drugpolymer compositions at different temperatures and finally the spinodal curve. The predicted behavior of the binary system was evaluated through X-ray diffraction, differential scanning calorimetry, and in vitro dissolution studies. The results suggest possibility of employing interaction parameter as preliminary tool for the estimation of drug-polymer miscibility.

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a b s t r a c tOur goals were to evaluate the effects of (i) hydrostatic pressure alone and (ii) its combined effect with shear stress during compaction, on the polymorphic transformation (form C / A) of a model drug, chlorpropamide. The powder was either subjected to hydrostatic pressure in a pressure vessel or compressed in a tablet press, at pressures ranging from 25 to 150 MPa. The overall extent of phase transformation was determined by powder X-ray diffractometry, whereas 2D-X-ray diffractometry enabled quantification of the spatial distribution of phase composition in tablets. Irrespective of the pressure, the extent of transformation following compaction was higher than that because of hydrostatic pressure alone, the difference attributed to the contribution of shear stress experienced during compaction. At a compression pressure of 25 MPa, there was a pronounced gradient in the extent of phase transformation when monitored from radial tablet surface to core. This gradient decreased with increase in compression pressure. Four approaches were attempted to minimize the effect of compression-induced phase transformation: (a) site-specific lubrication, (b) use of a viscoelastic excipient, (c) ceramic-lined die, and (d) use of cavity tablet. The ceramic-lined die coupled with site-specific lubrication was most effective in minimizing the extent of compression-induced phase transformation.