A. K. Dorle

Liposomes as a carrier for oral administration of insulin: Effect of formulation factors

The present work was undertaken to study the effect of liposome formulation factors on its efficiency as a carrier for oral administration of insulin. The insulin-liposomes were prepared by two methods: solvent evaporation hydration and solvent spherule evaporation, with various variables such as concentration of insulin (I), lecithin (L), cholesterol (C), and Tween-80 (T). It was found that the insulin-liposomes when administered orally could produce hypoglycaemia. Variation in liposome composition was found to affect the efficiency of liposome as a carrier for oral administration of insulin. A liposome system containing L, 100 mg; C, 20 mg; I, 150 units; T, 1 per cent v/v, and prepared by the solvent spherule evaporation method was found to be most effective. The effect of insulin-liposome had prolonged action in diabetes-induced rabbits compared with that in normal rabbits. The results of the insulin-liposome system were comparable with the action of 1 unit of insulin/kg administered subcutaneously.

Study of Rosin and Rosin esters as coating materials

Rosin esters were prepared by heating glycerol, sorbitol and mannitol. Aspirin granules were coated with solution of Rosin and Rosin esters in acetone. The coated granules were studied for moisture absorption, dissolution studies, and ageing studies. The results showed that rosin-coated granules release less than 10% drug in gastric media in 3 h and more than 75% drug in 15 min in intestinal media. Rosin can be used as enteric coating material. Rosin esters give quick release in gastric media and delayed release in intestinal media. Ageing does not have a significant effect in release characteristics. Rosin and Rosin esters are widely used as film-forming plasticizers for moisture protection and find use in chlorinated rubber, vinyl resins, paints and varnishes. Glycerol ester of Rosin has been used as an anhydrous binding agent in tablet formulation (Surowiecki et al., 1971). A formula is patented for repeat action beadlets using abietic acid-type Rosin and Zein (Butler and Vance, 1968). This communication explains the application of Rosin and Rosin esters as coating materials. It was found that Rosin can be used for moisture protection and enteric coating purpose while Rosin esters can be used for controlled release. Rosin esters of glycerol (Kogan, 1932) mannitol and sorbitol (Brown and Geopp, 1938) were prepared by heating Rosin (4 parts) and glycerol (1 part) at 210-220°C. Heating was continued until there was no further drop in acid value of the sample withdrawn from the reaction. The whole mass was poured in water, to remove excess of alcoholic compound, with constant stirring, filtered and dried at 50°C in the oven overnight.

Study of rosin glycerol esters as microencapsulating materials

Rosin esters were prepared by heating rosin with glycerol and intermediate reaction products with different acid values were withdrawn. Salicylic acid granules were encapsulated using a 10 per cent solution of rosin esters in acetone. The coated microcapsules were evaluated for moisture absorption, flow properties and dissolution studies. The results showed that rosin and rosin-glycerol intermediates with acid values of 122, 105 and 55 had excellent moisture protection properties. Dissolution studies showed that these could be used for delayed release of drug.

Release kinetics of drugs from rosin-glycerol ester microcapsules prepared by solvent evaporation technique

Rosin-glycerol ester microcapsules containing sulphadiazine were prepared by solvent evaporation technique. The goodness of fit of the release data was tested with first order, Higuchi matrix model and Hixon-Crowell cube root law. All these models were sufficiently linear. Application of the differential rate treatment showed that release from most of the microcapsules followed first order equation. Whereas up to 40-50 per cent of release, a zero order, membrane controlled kinetics was observed, the release is apparently first order under nonsteady, state conditions.

Study of abietic acid glycerol derivatives as microencapsulating materials

Abietic acid (85 per cent pure) was extracted from rosin N Grade and further standardized. Abietic acid derivatives were prepared by heating abietic acid with glycerol and intermediate reaction products with different acid values were collected. Salicylic acid granules were encapsulated using a 10 per cent solution of abietic acid and its derivatives by standard spray pan technique. The coated microcapsules were evaluated for moisture absorption, dissolution and flow properties. The result showed that abietic acid glycerol derivatives, AaG-54 and AaG-20 had better moisture protection properties. Dissolution studies indicate that these derivatives could be used for delayed release of drugs.

Effect of variables on the preparation of shellac microcapsules by solvent evaporation technique: Part 1

Abstract Shellac microcapsules were prepared by phase separation by solvent evaporation using sulphadiazine as a model drug. Appropriate mixtures of the drug were made in solution of shellac in isobutanol and emulsified in aqueous bentonite suspension. The microcapsules were obtained by evaporating the solvent at elevated temperatures. The effect of variables such as the amount of drug, bentonite concentration and stirring speed were studied. The proposed method is simple and free from agglomeration and coalescence.

Preparation and in vitro evaluation of rosin microcapsules: solvent evaporation technique

Free flowing, spherical rosin microcapsules were prepared by a method based on phase separation by solvent evaporation. Bentonite was used to prevent the agglomeration and coalescence of the dispersed polymer droplets. The effect of varying the core to coat ratio on micrometric and dissolution properties has been described.

A new technique for the encapsulation of water insoluble drugs using ethyl cellulose

A new technique for encapsulation of water insoluble drugs has been developed utilizing ethyl cellulose as a wall forming material. Ethyl cellulose was dissolved in a water immiscible, volatile organic solvent, containing sulphadiazine as a model drug. This dispersion was emulsified into an aqueous bentonite suspension and phase separation was induced by solvent evaporation. The effect of bentonite concentration, core to coat ratio, organic solvent, speed of agitation and temperature was studied with respect to the microcapsule size and size distribution, drug content, in vitro release and surface characteristics.

Effect of solvents on the characteristics of rosin walled microcapsules prepared by a solvent evaporation technique

Rosin microcapsules were prepared by a solvent evaporation technique using solvents with different rates of evaporation. Sulphadiazine was used as a model drug. The microcapsules were studied for their size, drug content, wall thickness, surface characteristics and in vitro release. The mean diameter increased and the drug content decreased as the rate of evaporation of the solvent increased. Fast evaporating solvents produced thick walled microcapsules with innumerable surface pores/cracks compared with slow evaporating solvents.

A study on the zeta potential of microcapsules during ageing

Gelatin, methylcellulose and agar microcapsules were prepared with and without suphadiazine. The zeta potential of these microcapsules was measured at regular intervals during ageing at 45 degrees C. An initial sharp rise in zeta potential is followed by a progressive decrease. Zeta potential could prove to be a useful parameter to study the changes occurring in the encapsulating material of microcapsules during ageing.