Suspensions of prolonged-release diclofenac-Eudragit® and ion-exchange resin microcapsules: II. Improved dissolution stability

PURPOSE

The stability of prolonged release 100 microm -size ion-exchange resin (IER) diclofenac microcapsules (prepared by the Wurster process) and coated with Eudragit RS30D was evaluated using dissolution analysis.

METHODS

The IER microcapsules were suspended in 0.1% methylcellulose and stored at 23 and 37 degrees C and the dissolution study conducted over a 6-month period. The surface morphology of the microcapsules was examined using scanning electron microscopy (SEM).

RESULTS

The dissolution of the suspensions stored at 23 degrees C on day 1 or 7 and was similar to that of day 30 with slightly faster dissolution on day 60. In contrast, release from suspensions stored at 37 degrees C decreased with storage. The decrease in dissolution with increased temperature was possibly due to the polymer relaxation (micromelting) that was enough to seal the drug within the matrix, resulting in slow dissolution. SEM of the suspended microcapsules correlated with the dissolution data, i.e. the surfaces of microcapsule stored at 37 degrees C showed decreased roughness or smoothening and closing of pores with time and, hence, retardation of drug release, compared with samples stored at 23 degrees C. The dissolution kinetics (shown by the linearity of Bt vs. time profiles) indicated that release mechanism was diffusion.

CONCLUSIONS

The suspensions of diclofenac IER microcapsules were stable up to 30 days at ambient temperature, which makes the formulation potentially useful as reconstitutable product.

Dissolution stability studies of suspensions of prolonged-release diclofenac microcapsules prepared by the Wurster process: I. Eudragit-based formulation and possible drug-excipient interaction

The aim was to evaluate possible interaction in solid and liquid state of the drug with formulation excipients consequent to very fast drug release of diclofenac-Eudragit prolonged release microcapsules. The microcapsules were prepared by drug layering on calcium carbonate cores and coated with Eudragit RS 30D and L30D-55 as previously reported. Suspension of the microcapsules was prepared using microcrystalline cellulose/sodium carboxymethyl cellulose (Avicel CL-611) as medium. In vitro dissolution testing of the suspension was done, and, based on the dissolution results, possible interaction between diclofenac and Eudragit and Avicel in the medium was studied. Powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC) analyses were performed using 1:1 binary, 1:1:1 ternary mixtures and a ratio equivalent to that in the formulation. The mixtures were prepared by mixing the dispersions--Eudragit RS 30D or L30D-55 with the drug or other components, followed by drying at 60 degrees C for 48 h. Dry mixing was done using the powder equivalents of the polymers, Eudragit RS PO and L100-55, Avicel and calcium carbonate. In vitro dissolution of the suspended microcapsules showed a very fast release after 48 h (T50 = <1 h) compared to the solid microcapsules (T50 = 6 h). DSC curves of the formulation components or microcapsules did not show the characteristic endothermic peak of diclofenac at 287 degrees C. Powder X-ray diffraction of the binary or ternary mixtures of diclofenac and Eudragit polymers indicated reduction, shift or modification of the crystalline peaks of the drug or excipients at 2theta of 12 degrees and 18 degrees , suggestive of interaction. Some changes in drug peak characteristics at 18 degrees and 23 degrees were observed for Avicel/drug mixture, though not significant. The DSC curves of the binary mixture of diclofenac co-dried with liquid forms of Eudragit (i.e. RS 30D or L30D-55) revealed greater interaction compared to the curves of drug and powdered forms of Eudragit (RS PO or L100-55). This was depicted by greater shift in fusion points of the mixtures relative to the drug. However, comparing the RS and L-type Eudragit, the latter generally showed greater interaction with the drug. Interaction between diclofenac and L-type Eudragit polymers can occur in liquid formulations.

Elucidation of solution state complexation in wet-granulated oven-dried ibuprofen and beta-cyclodextrin: FT-IR and 1H-NMR studies

The effect of oven-dried wet granulation on the complexation of beta-cyclodextrin with ibuprofen (IBU) in solution was investigated using Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (1H NMR), and molecular modeling. Granulation was carried out using 5 mL of three different granulating solvents; water, ethanol (95% v/v), and isopropanol and the granules were oven-dried at 60 degrees C for 2 h. The granules were compared to oven-dried physical mixture and conventionally prepared complex. Phase solubility study was performed to investigate the stability of the granulation-formed complexes in solution. FT-IR was used to examine the complexation in the granules while 1H NMR, and molecular modeling studies were carried out to determine the mechanism of complexation in the water-prepared granules. The solubility studies suggested a 1:1 complex between IBU and betaCD. It also showed that the stability of the complex in solution was in the following order with respect to the granulating solvents: ethanol > water > isopropanol. The FT-IR study revealed a shift in the carboxylic acid stretching band and decrease in the intensities of the C-H bending bands of the isopropyl group and the out-of-plane aromatic ring, of IBU, in granules compared to the oven-dried physical mixture. This indicated that granules might have some extent of solid state complexation that could further enhance dissolution and the IBU-betaCD solution state complexation. 1H NMR showed that water prepared oven-dried granules had a different 1H NMR spectrum compared to similarly made oven-dried physical mixture, indicative of complexation in the former. The 1H NMR and the molecular modeling studies together revealed that solution state complexation from the granules occurred by inclusion of the isopropyl group together with part of the aromatic ring of IBU into the betaCD cavity probably through its wider side. These results indicate that granulation process induced faster complexation in solution which enhances the solubility and the dissolution rate of poorly soluble drugs. The extent of complexation in the granules was dependent on the type of solvent used.

Enhancement of ibuprofen dissolution via wet granulation with beta-cyclodextrin

The purpose was to investigate the effect of wet granulation with beta-cyclodextrin (betaCD) on the enhancement of ibuprofen (IBU) dissolution. The effect of the granulation variables on the physical properties as well as the dissolution of tablets prepared from these granules was also examined. Granulation was performed using three granulating solvents: water, ethanol (95 vol%), and isopropanol. Granules were either oven-dried for 2 h or air-dried for 3 days. The granules or respective physical mixtures were compressed into tablets. Powder X-ray diffraction showed that oven-dried granulation resulted in less amorphous entities thatfacilitated IBU-betaCD complexation in solution and enhanced the dissolution of the corresponding tablets compared to the physical mixture with or without oven drying. In contrast, air-dried granulation did not cause any differences in the X-ray diffraction pattern (crystallinity) or the dissolution compared to the physical mixture without drying. Isopropanol and water, as granulating solvents, enhanced the dissolution of the oven-dried batches more than ethanol. The Differential scanning calorimetry (DSC) and Thermogravimetric analysis (TGA) data showed that tablets prepared from oven-dried granules, but not air-dried granules, had lower AH values and percent loss in weight, respectively, than those prepared from the physical mixture as a result of the expulsion of the water molecules from the betaCD cavity and enhancement of the complexation in solution. These results showed that oven-dried granulation of IBU and betaCD provided faster IBU dissolution than the physical mixture; air-dried granulation did not substantially affect the dissolution of IBU.

Use of ion-exchange resins to prepare 100 microm-sized microcapsules with prolonged drug-release by the Wurster process

Ion-exchange resin (IER)--drug complexes were used as core materials to explore their capability to prepare a 100 microm-sized, highly drug-incorporated microcapsule with a prolonged drug release by the Wurster process. Diclofenac sodium was loaded into Dowex 1-X2 fractionated into 200--400 mesh and subsequently microencapsulated with two types of aqueous colloidal polymer dispersion, Aquacoator Eudragit RS30D. The mass median diameter and drug content of the microcapsules thus obtained were 98 microm and 46% with Aquacoat, and 95 microm and 50% with Eudragit RS30D, respectively. Each microcapsule was obtained at a product yield of 94%. The rate of drug release from the microcapsules was highly dependent on the encapsulating materials. For the microcapsules coated with Aquacoat, diclofenac sodium was found to be rapidly released over 4 h, even at a 25 wt% coating level because of cracks on the microcapsule surfaces resulting from the swelling stress of the drug-loaded IER cores. In contrast, significantly prolonged drug-release was achieved in the microcapsules prepared with Eudragit RS30D: even such a very low coating level as 3 wt% provided an exceptionally prolonged drug-release over 24 h. The results indicated that the use of IER along with a flexible coating material would be a feasible way to prepare a prolonged release type of microcapsules with a diameter of 100 microm and a drug content of more than 50% by the Wurster process.

Hygroscopicity, phase solubility and dissolution of various substituted sulfobutylether beta-cyclodextrins (SBE) and danazol-SBE inclusion complexes

The aim of the present work was to characterize hygroscopicity, phase solubility and dissolution properties for various substituted sulfobutylether beta-cyclodextrins (SBEs) and danazol-SBE inclusion complexes. Moisture sorption was measured using a symmetric gravimetric analyzer. The complexes were characterized by powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Moisture sorption isotherms for the SBEs and the complexes showed low moisture sorption at RH <60%. The moisture absorption desorption isotherms for the various SBEs showed very little hysteresis, indicating almost complete desorption. Moisture adsorbed by the various SBE was in the order SBE 7>SBE 4>SBE 5 at 95% RH. Powder XRD data for complexes showed the disappearance of characteristic crystalline peaks for danazol or the formation of amorphous entities and DSC showed the disappearance of the peak of fusion of danazol indicating complex formation. Phase solubility of danazol with various substituted SBEs indicated 1:1 stoichiometry of complexes. The apparent stability constant, as determined by the method of Higuchi and Connors, increased as the degree of substitution of SBEs increased and decreased as the temperature increased. The dissolution of the complexes was significantly greater than that of the corresponding physical mixtures indicating that the formation of amorphous complex increased the solubility of poorly soluble danazol. More than 85% of danazol was released in <10 min, compared to 15% danazol release from the physical mixtures.