An investigation of flurbiprofen polymorphism by thermoanalytical and spectroscopic methods and a study of its interactions with poly-(ethylene glycol) 6000 by differential scanning calorimetry and modelling

Polymorphism in Solid Dispersions

Solid dispersions embed active pharmaceutical ingredients in polymeric carriers to improve their solubility. Three solid dispersion preparation techniques are typically employed: solvent evaporation, solvent-fusion, and fusion methods. Although these are also widely recommended as preparative methods for phase diagram determination, few examples exist concerning their effect on the resulting polymorph, once the solid dispersion is produced. In this study, the influence of these methods on the polymorphic form obtained in crystalline solid dispersions (CSDs) composed of flufenamic acid (FFA) and poly(ethylene glycol) was investigated. The physical mixtures and CSDs were characterized by powder X-ray diffraction, infrared spectroscopy, and differential scanning calorimetry. The results reveal that the fusion method leads to concomitant polymorphs (mainly FFA I and III) in the CSDs. In contrast, the solvent evaporation and solvent-fusion methods lead to FFA III. Collectively, these results demonstrate that preparative methods have a significant influence on the phase diagrams determined (average relative deviation ≤8%), which are often used to justify the design space of manufacturing processes, including those deemed "continuous." Consequently, choosing a preparation method that results in the desired polymorph is crucial to ensure accurate determination of phase diagrams and critical quality attributes of formulations.

Spectroscopic and DFT studies of flurbiprofen as dimer and its Cu(II) and Hg(II) complexes

The vibrational study in the solid state of flurbiprofen and its Cu(II) and Hg(II) complexes was performed by IR and Raman spectroscopy. The changes observed between the IR and Raman spectra of the ligand and of the complexes allowed us to establish the coordination mode of the metal in both complexes. The comparative vibrational analysis of the free ligand and its complexes gave evidence that flurbiprofen binds metal (II) through the carboxylate oxygen. The fully optimized equilibrium structure of flurbiprofen and its metal complexes was obtained by density functional B3LYP method by using LanL2DZ and 6-31 G(d,p) basis sets. The harmonic vibrational frequencies, infrared intensities and Raman scattering activities of flurbiprofen were calculated by density functional B3LYP methods by using 6-31G(d,p) basis set. The scaled theoretical wavenumbers showed very good agreement with the experimental values. The electronic properties of the free molecule and its complexes were also performed at B3LYP/6-31G(d,p) level of theory. Detailed interpretations of the infrared and Raman spectra of flurbiprofen are reported. The UV-vis spectra of flurbiprofen and its metal complexes were also investigated in organic solvents.

The Binary Eutectic of NSAIDs and Two-Phase Liquid System for Enhanced Membrane Permeation

The eutectic properties of binary mixtures of some nonsteroidal anti-inflammatory drugs (NSAIDs) with ibuprofen were studied using differential scanning calorimetry (DSC) and phase equilibrium diagrams. The melting points of selected NSAIDs were significantly depressed due to binary eutectic formation with ibuprofen. Ketoprofen and ibuprofen were selected to study the effect of eutectic formation on membrane permeation using Franz diffusion cells and snake skin as the model membrane. The presence of aqueous isopropyl alcohol (IPA) was necessary to completely transform the solid drugs into an oily state at ambient temperature. As much as the 99.6% of ibuprofen and the 88.8% of ketoprofen added were found in the oily phase of the two-phase liquid system formed when aqueous IPA was added to the eutectic mixture. Due to the high drug concentration in the oily phase, and maximum thermodynamic activity, the two-phase liquid system showed enhanced membrane permeation rates of ibuprofen (37.5 microg/cm2/hr) and ketoprofen (33.4 microg/cm2/hr) compared to other reference preparations used.

Dissolution, Solubility, XRD, and DSC Studies on Flurbiprofen-Nicotinamide Solid Dispersions

Flurbiprofen-nicotinamide solid dispersions were prepared by the fusion method. The solid dispersions were evaluated for dissolution rate. The drug-carrier interaction in the liquid and solid states were studied by using phase solubility analysis, phase diagram, X-ray diffraction (XRD), and differential scanning calorimentry (DSC). Solid dispersions gave fast and rapid dissolution of flurbiprofen compared with the pure drug and the physical mixture. Phase diagram and DSC indicated that flurbiprofen and nicotinamide form a eutectic mixture. The aqueous solubility of flurbiprofen was enhanced in the presence of nicotinamide.

New form discovery for the analgesics flurbiprofen and sulindac facilitated by polymer-induced heteronucleation

The selection and discovery of new crystalline forms is a longstanding issue in solid-state chemistry of critical importance because of the effect molecular packing arrangement exerts on materials properties. Polymer-induced heteronucleation has recently been developed as a powerful approach to discover and control the production of crystal modifications based on the insoluble polymer heteronucleant added to the crystallization solution. The selective nucleation and discovery of new crystal forms of the well-studied pharmaceuticals flurbiprofen (FBP) and sulindac (SUL) has been achieved utilizing this approach. For the first time, FBP form III was produced in bulk quantities and its crystal structure was also determined. Furthermore, a novel 3:2 FBP:H(2)O phase was discovered that nucleates selectively from only a few polymers. Crystallization of SUL in the presence of insoluble polymers facilitated the growth of form I single crystals suitable for structure determination. Additionally, a new SUL polymorph (form IV) was discovered by this method. The crystal forms of FBP and SUL are characterized by Raman and FTIR spectroscopies, X-ray diffraction, and differential scanning calorimetry.

Factors Affecting the Formation of Eutectic Solid Dispersions and Their Dissolution Behavior

The objective of this work was to obtain a fundamental understanding of the factors, specifically the properties of poorly water-soluble drugs and water-soluble carriers, which influence predominantly, the formation of eutectic or monotectic crystalline solid dispersion and their dissolution behavior. A theoretical model was applied on five poorly water-soluble drugs (fenofibrate, flurbiprofen, griseofulvin, naproxen, and ibuprofen) having diverse physicochemical properties and water-soluble carrier (polyethylene glycol (PEG) 8000) for the evaluation of these factors. Of these, two drugs, fenofibrate and flurbiprofen, and PEG of different molecular weights (3350, 8000, and 20000), were chosen as model drugs and carriers for further investigation. Experimental phase diagrams were constructed and dissolution testing was performed to assess the performance of the systems. The theoretical model predicted the formation of eutectic or monotectic solid dispersions of fenofibrate, griseofulvin, ibuprofen, and naproxen with PEG, holding the contribution of specific intermolecular interactions between compound and carrier to zero. In the case of the flurbiprofen-PEG eutectic system, intermolecular interactions between drug and polymer needed to be taken into consideration to predict the experimental phase diagram. The results of the current work suggest that the thermodynamic function of melting point and heat of fusion (as a measure of crystal energy of drug) plays a significant role in the formation of a eutectic system. Lipophilicity of the compound (as represented by cLog P) was also demonstrated to have an effect. Specific interactions between drug and carrier play a significant role in influencing the eutectic composition. Molar volume of the drug did not seem to have an impact on eutectic formation. The polymer molecular weight appeared to have an impact on the eutectic composition for flurbiprofen, which exhibits specific interactions with PEG, whereas no such impact of polymer molecular weight on eutectic composition was observed for fenofibrate, which does not exhibit specific interactions with PEG. The impact of polymer molecular weight on dissolution of systems where specific drug-polymer interactions are exhibited was also observed. The current work provides valuable insight into factors affecting formation and dissolution of eutectic systems, which can facilitate the rational selection of suitable water-soluble carriers.

Design and evaluation of colon specific drug delivery system containing flurbiprofen microsponges

The purpose of this study was to design novel colon specific drug delivery system containing flurbiprofen (FLB) microsponges. Microsponges containing FLB and Eudragit RS 100 were prepared by quasi-emulsion solvent diffusion method. Additionally, FLB was entrapped into a commercial Microsponge 5640 system using entrapment method. Afterwards, the effects of drug:polymer ratio, inner phase solvent amount, stirring time and speed and stirrer type on the physical characteristics of microsponges were investigated. The thermal behaviour, surface morphology, particle size and pore structure of microsponges were examined. The colon specific formulations were prepared by compression coating and also pore plugging of microsponges with pectin:hydroxypropylmethyl cellulose (HPMC) mixture followed by tabletting. In vitro dissolution studies were done on all formulations and the results were kinetically and statistically evaluated. The microsponges were spherical in shape, between 30.7 and 94.5microm in diameter and showed high porosity values (61-72%). The pore shapes of microsponges prepared by quasi-emulsion solvent diffusion method and entrapment method were found as spherical and cylindrical holes, respectively. Mechanically strong tablets prepared for colon specific drug delivery were obtained owing to the plastic deformation of sponge-like structure of microsponges. In vitro studies exhibited that compression coated colon specific tablet formulations started to release the drug at the 8th hour corresponding to the proximal colon arrival time due to the addition of enzyme, following a modified release pattern while the drug release from the colon specific formulations prepared by pore plugging the microsponges showed an increase at the 8th hour which was the time point that the enzyme addition made. This study presents a new approach based on microsponges for colon specific drug delivery.

Flurbiprofen-loaded nanospheres: analysis of the matrix structure by thermal methods

We report the preparation and evaluation of flurbiprofen loaded-poly-epsilon-caprolactone nanospheres obtained by solvent displacement method. Characterization by thermal methods, infrared spectroscopy and X-ray diffraction analysis can reveal the dispersion state of the drug inside the nanospheres. Such information predicts the stability of the particles and the drug release behaviour. The study has indicated the presence of a molecular dispersed system. In addition, construction of a phase diagram has allowed us to determine the drug/polymer ratios at which flurbiprofen has the highest entrapment efficiency.

Demonstration of the terms enantiotropy and monotropy in polymorphism research exemplified by flurbiprofen

The thermodynamic terms enantiotropy and monotropy are demonstrated by means of solid-state analytical results of polymorphous flurbiprofen (FBP). Vibrational spectra, differential scanning calorimetry (DSC), and thermomicroscopy investigations as well as X-ray powder patterns for three modifications of FBP are described. The melting points are mod. I 113-114 degreesC (enthalpy of fusion 27.9 +/- 0.2 kJ mol-1) for modification I (mod. I), 92 degreesC for mod. II, and 87 degreesC for mod. III. The true densities of mod. I (1.279 +/- 0.001 g cm-3) and mod. II (1.231 +/- 0.002 g cm-3) were measured at 25 degreesC. Modification I (commercial product) is the thermodynamically stable crystal form from absolute zero to its melting point. Modification II was crystallized on a gram scale from a warm saturated solution of FBP in n-heptane and rapid cooling of the solution to -18 degreesC. Modification I is monotropically related to mod. II and mod. III, due to application of the density rule and the entropy-of-fusion rule. The thermodynamic relationships between the three modifications are demonstrated by a semischematic energy/temperature diagram. Theoretical vapor pressure/temperature diagrams and energy/temperature diagrams are compared and briefly discussed.

An investigation of FB interactions with poly(ethylene glycol) 6000, poly(ethylene glycol) 4000, and poly-epsilon-caprolactone by thermoanalytical and spectroscopic methods and modeling

The interactions between flurbiprofen (FB) and different polymers are studied in order to improve the bioavailability of FB. FB-polymer phase diagrams [poly(ethylene glycol) (PEG) 4000, PEG 6000, and poly-epsilon-caprolactone] were constructed and compared with the modeling diagrams. Thermoanalytical methods (differential scanning calorimetry, thermomicroscopy) were used to construct the phase diagrams. Thermodynamic data were used to model the FB-polymer systems. The construction of the FB-polymer phase diagrams showed the existence of a stable invariant called "eutectic" characterized by (XE)exp, (TfE)exp, and (DeltaHfE)exp, the experimental eutectic composition, the experimental temperature, and the enthalpy of eutectic melting, respectively. Modeling confirmed the values for these parameters and was used to evaluate the different Flory-Huggins parameters chi for each FB-polymer mixture. chi values and the infrared spectra confirm that the interactions due to hydrogen bonds between FB and PEG 4000 are more numerous than between FB and PEG 6000 and also more numerous than between FB and poly-epsilon-caprolactone.