Emulsions drug release

Chloropromazine (8—34 wt% loading) has been microencapsulated in PCL-cellulose propionate blends by the emulsion solvent evaporation method (61). Phase separation for some ratios of the two polymers was detectable by SEM. The release rate from microcapsules in the size range of 180-250 pm in vitro (Fig. 11) was directly proportional to the PCL content of the blend, the half-life (50% drug release)... 

T Koizumi, W Higuchi. Analysis of data on drug release from emulsions II. Pyridine release from water-in-oil emulsions as a function of pH. J Pharm Sci 57 87, 1968. 

Sustained release from disperse systems such as emulsions and suspensions can be achieved by the adsorption of appropriate mesogenic molecules at the interface. The drug substance, which forms the inner phase or is included in the dispersed phase, cannot pass the liquid ciystals at the interface easily and thus diffuses slowly into the continuous phase and from there into the organism via the site of application. This sustained drug release is especially pronounced in the case of multilamellar liquid crystals at the interface. 

In the pharmaceutics literature, an application-triggered drug release from an O/W emulsion recipe has been reported. The application of emulsions in the pharmaceutical industry is very important, and a large number of references are found in the current literature. 

The self-emulsifying behaviour of a binary nonlonlc surfactant vegetable oil mixture has been shown to be dependant on both temperature and surfactant concentration. The quality of the resulting emulsions as assessed by particle size analysis showed that manipulation of these parameters can result In emulsion formulations of controlled droplet size and hence surface area. Such considerations are Important when the partition of lipophilic drugs Into aqueous phases and drug release rates are considered. 

In vitro release data of propranolol hydrochloride from the four formulations evaluated ovr a 24 h period are shown in Table 2. The decreasing rank order of drug release from these samples was observed to be as follows Methocel matrix> Avicel CL-611 matrix>PVA-gelatin matrix>emulsion base. The Methocel matrix, formulation A, exhibited the maximum release of the drug, whereas the drug released was at a minimum from the PVA-gelatin matrix, formulation... 

In an effort to develop an effective bioadhesive system for buccal administration, insulin was encapsulated into polyacrylamide nanoparticles by the emulsion solvent evaporation method [98]. Though nanoparticle formation ensures even distribution of the drug, pelleting of the nanoparticles was performed to obtain three-dimensional structural conformity. In addition, it was hypothetized that the pelletized particles will remain adhered to the mucosa, leading to good absorption. While studying bioadhesion and drug release profiles, it was found that the... 

In the preparation of microspheres by solvent evaporation from oil-in-water emulsions, the presence of base (NaOH) was found to enhance the release of thioridazine from polylactide micro-spheres. The amount of drug release as a function of time was dependent on the amount of base added to the aqueous phase of the emulsion. Scanning electron micrographs indicate that this increased drug release may be due to modification of the internal structure of the microspheres by sodium hydroxide during fabrication. 

Drug release may be affected by a number of process parameters such as drug loading, polymer molecular weight, polymer composition, initial concentration of the polymer in the organic phase of the emulsion, amount of emulsifier, stirring speed, vacuum pressure, solvent evaporation time and temperature. These parameters were kept constant and only the amount of NaOH was varied. Therefore, changes in the in vitro release curves should reflect only the effect of NaOH in various concentrations. ... 

The effect of NaOH on drug release was examined with microspheres prepared with thioridazine and two biodegradable polymers. The wall-forming polymers were poly(DL-lactide) and poly(L-lactide). Sodium oleate was used as the emulsifier, with the exception of one set of experiments where the emulsions were stabilized with polyvinyl alcohol. 

In order to determine whether the effect of NaOH was specific to the use of sodium oleate as the emulsifier, microspheres were also prepared using polyvinyl alcohol to stabilize the emulsion. Figure 3 indicates that there was only a moderate increase in drug release by the addition of NaOH to the emulsion. 

Drug release of thioridazine was enhanced when the microspheres were prepared in the presence of base. The effect was dependent on the amount of NaOH added to the aqueous phase of the emulsion prior to the solvent evaporation step. 

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