Hot stage extrusion of p-amino salicylic acid with EC using CO2 as a temporary plasticizer.

The aim of the current research project was to explore the possibilities of combining pressurized carbon dioxide with hot stage extrusion during manufacturing of solid dispersions of the thermally labile p-aminosalicylic acid (p-ASA) and ethylcellulose 20cps (EC 20cps) and to evaluate the ability of the pressurized gas to act as a temporary plasticizer. The thermal stability of the p-ASA was investigated using DSC, TGA and HPLC. The compound decomposes completely upon melting. Below 110 degrees C and under atmospheric conditions, the compound is thermally stabile for 10min. Pressurized carbon dioxide was injected into a Leistritz Micro 18 intermeshing co-rotating twin-screw melt extruder using an ISCO 260D syringe pump. Carbon dioxide acted as plasticizer for p-ASA/EC 20cps, reducing the processing temperature during the hot stage extrusion process. HPLC showed that without carbon dioxide injection, approximately 17% of p-ASA degraded, while less than 5% degraded with CO(2) injection. The experiments clearly showed that injecting pressurized carbon dioxide broadens the application of hot stage extrusion to thermally labile compounds in a one step process.

Preparation and physicochemical characterization of biodegradable nerve guides containing the nerve growth agent sabeluzole.

The objective of this study was to develop and characterize a biodegradable drug-loaded nerve guide for peripheral nerve regeneration. Sabeluzole, a nerve growth agent, was selected as model compound. Four biodegradable polymers were selected for this study: a copolymer of polylactic acid and polycaprolactone (PCL); a copolymer of polyglycolic acid and polycaprolactone PCL; a copolymer of PCL/polydioxanone (PDO) and PDO. Placebo and drug loaded nerve guides were obtained by melt compression and melt extrusion. It was observed that melt compression and melt extrusion are feasible techniques to prepare the nerve guides. Based on the physicochemical characterization, all samples show absence of crystalline sabeluzole, indicating the formation of an amorphous dispersion. The in vitro release measurements show that the release of sabeluzole is complete, reproducible and can be controlled by the proper selection of the polymer. The release mechanism for all samples follows Fickian release behaviour.

Study of the physicochemical properties and stability of solid dispersions of loperamide and PEG6000 prepared by spray drying.

Solid dispersions of PEG6000 and loperamide-a poorly water-soluble agent-were prepared by spray drying. Their physicochemical properties were evaluated immediately after preparation. The dissolution was higher than that of pure crystalline loperamide. DSC- and XRD-measurements revealed that in the dispersions, loperamide is partially present in the crystalline state. A eutectic state diagram was obtained. The samples containing 20% loperamide were stored under different conditions (40 degrees C and 0% RH, 25 degrees C and 52% RH, 4 degrees C and 0% RH) to investigate their stability as a function of time. The dissolution properties deteriorate upon storage at high temperature (40 degrees C and 0% RH) and in conditions of higher relative humidity (25 degrees C and 52% RH). The DSC-curves clearly indicate an increase in the amount of crystalline compound under these conditions. From these observations it could be concluded that loperamide, which is partially crystalline and partially amorphous in the freshly prepared samples, continues to crystallize under these conditions, resulting in progressively poorer dissolution properties.

Physical stability of the amorphous state of loperamide and two fragment molecules in solid dispersions with the polymers PVP-K30 and PVP-VA64.

The purpose of the present study was to investigate the impact of intermolecular forces on the stability of the amorphous state of loperamide and two of its fragment molecules (4-dimethylamino-N,N-dimethyl-2,2-diphenyl-butyramide (F1) and 4-(4-chlorophenyl)-4-piperidinol (F2)) in solid dispersions with PVP-K30 and PVP-VA64. The stability of originally homogeneous and amorphous dispersions was investigated under different storage conditions. The chemical stability of the compounds was evaluated with HPLC. TGA-analysis was used in order to assess the amount of water in the samples, whereas MT-DSC-measurements were performed to investigate changes in the physical state of the compounds caused by the storage procedure. TGA-analysis reveals a higher uptake of water in humid conditions of the dispersions with PVP-K30 in comparison to those with PVP-VA64, hereby reflecting the more hydrophilic nature of the former polymer. This water acts as a plasticizing agent resulting in an increased mobility and decreased glass transition temperature. Since the degree of supersaturation and the molecular mobility have an influence on the stability of the amourphous state, both parameters were assessed. With respect to the degree of supersaturation of the compounds in the dispersions, the materials seem to be very much alike. Therefore it was postulated that the induction of crystallization in the F1/polymer dispersions stored at high RH (52%) is due to higher molecular mobility of this compound in the dispersions in comparison to F2. The hydrogen bonds that are being formed between F2 and the polymers reduce its mobility and secure this compound from crystallization upon storage, thus indicating the importance of specific interactions with respect to stability issues of solid dispersions. No hydrogen bonds are formed between F1 and the polymers. As a result, the stability of the amorphous state of the compound is being compromised and crystallization takes place. Loperamide, that also does not form hydrogen bonds with the polymers, is less susceptible to crystallization due to its intrinsic good glass forming properties.

The effect of pressurized carbon dioxide as a temporary plasticizer and foaming agent on the hot stage extrusion process and extrudate properties of solid dispersions of itraconazole with PVP-VA 64.

The aim of the current research project was to explore the possibilities of combining pressurized carbon dioxide with hot stage extrusion during manufacturing of solid dispersions of itraconazole and polyvinylpyrrolidone-co-vinyl acetate 64 (PVP-VA 64) and to evaluate the ability of the pressurized gas to act as a temporary plasticizer as well as to produce a foamed extrudate. Pressurized carbon dioxide was injected into a Leistritz Micro 18 intermeshing co-rotating twin-screw melt extruder using an ISCO 260D syringe pump. The physicochemical characteristics of the extrudates with and without injection of carbon dioxide were evaluated with reference to the morphology of the solid dispersion and dissolution behaviour and particle properties. Carbon dioxide acted as plasticizer for itraconazole/PVP-VA 64, reducing the processing temperature during the hot stage extrusion process. Amorphous dispersions were obtained and the solid dispersion was not influenced by the carbon dioxide. Release of itraconazole from the solid dispersion could be controlled as a function of processing temperature and pressure. The macroscopic morphology changed to a foam-like structure due to expansion of the carbon dioxide at the extrusion die. This resulted in increased specific surface area, porosity, hygroscopicity and improved milling efficiency.

Phase behaviour analysis of solid dispersions of loperamide and two structurally related compounds with the polymers PVP-K30 and PVP-VA64.

The purpose of the present study was to investigate the influence of the structure of a poorly water soluble model drug (loperamide) on the phase behaviour in solid dispersions with PVP-K30. Dispersions with PVP-VA64, a less hydrophilic polymer, were investigated as well in order to study the influence of differences in polymer structure and water content of the samples. The solid dispersions of PVP-K30 or PVP-VA64 with loperamide as well as with two fragments of this molecule were prepared by spray drying. The amount of residual solvents and water was determined with GC and thermogravimetric analysis (TGA). The drug loading of the dispersions was determined using high performance liquid chromatography (HPLC). The solid state properties were evaluated using powder-XRD, IR-spectroscopy and MT-DSC. All mixtures containing loperamide proved to be completely amorphous, whereas the dispersions containing the fragments are only amorphous in case the polymer content is high. The phase diagrams that were constructed clearly show that loperamide exhibits a different behaviour in the solid dispersions than its two building blocks. They also point to the presence of specific intermolecular compound--polymer interactions in the dispersions of one of the fragments with the two polymers. This was confirmed by the IR-results. Despite structural similarities, interactions in dispersions containing loperamide are far less important. In dispersions containing high concentrations of the other fragment, the DSC curves give indications for polymorphism whereas IR and XRD-spectra point towards inclusion of solvent in these samples.