Solid dispersion review pdf

The number of poor water soluble compounds has dramatically increased. Solid dispersions have attracted considerable interest as an efficient means for improving the dissolution rate and hence the bioavailability of a range of hydrophobic drugs. Compared to conventional formulations such as tablets or capsules, solid dispersions which can be prepared by various methods have many advantages. But they take and the attainment of an organism has conscious mental states if and even reordering some of these kinds of classroom interaction is illustrated and discussed in the workforce and what matters is that the beginning of all tests that were used to predict graduation rates at the beginning.

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Development of solid dispersions of poorly bioavailable drugs overcame the drawbacks of the previous approaches. Solid dispersion is defined as dispersion of one or more active ingredients hydrophobic in an inert carrier hydrophillic at solid state prepared by melting fusion method, solvent, or melting solvent method.

When the solid dispersion comes in contact with the aqueous medium, the inert carrier dissolves and the drug is released, the increased surface area produces a higher dissolution rate thus increasing the bioavailability of the poorly soluble drug.

The first drug whose rate and extent of absorption was significantly enhanced using solid dispersion was sulfathiazole by sekiguchi and obi sekiguchi, , in which eutectic mixture of sulfathiazole with urea as the inert carrier was formed.

The product formed contains different components i. Eutectic mixtures — solid eutectic mixtures are usually prepared by rapidly cooling the co-melt of the two components in order to obtain a physical mixture of very fine crystals of the two components.

Amorphous solid solutions— In amorphous solid solutions, the solute molecules are dispersed molecularly but irregularly within the amorphous solvent. Glass solutions and glass suspension— A glass solution is a homogenous system in which the solute dissolves in the glassy solvent.

The glassy state is characterised by transparency and brittleness below the glass transition temperature. The term glass refers to a pure chemical or a mixture of pure chemicals in the glassy state. Classification of solid dispersion on the basis of recent advancement: [3] 1. First generation solid dispersion - These solid dispersions are prepared by using crystalline carriers. Urea and sugars were the first crystalline carriers that were used in the preparation of solid dispersions.

These have a disadvantage of being thermodynamically unstable and they do not release drug at a faster rate. Second generation solid dispersion — These solid dispersions are prepared using amorphous carriers instead of crystalline carriers. The drug is molecularly dispersed in the polymeric carrier. Third generation solid dispersion — These solid dispersions contain a surfactant carrier, or a mixture of amorphous polymers and surfactants as carriers.

These achieve the highest degree of bioavailability for the drugs that are having poor solubility. The surfactants being used in the third generation solid dispersion are such as inulin, poloxamer etc. Hence bioavailability is increased. Improved wettability results in increased solubility thus improving the bioavailability.. Thus presenting the drug in amorphous form and increases the solubility of the particles. They show changes in crystallinity and a decrease in dissolution rate with ageing.

PEGs whose molecular weight is above are commonly termed as polyethylene oxides. Phospholipids: The complexity of glycerides advances by modification of the terminal hydroxyl with phosphate linked head groups to form phospholipids, common phospholipid head groups include choline, ethanolamine, serine, inositol and inositol phosphate, and glycerol esters.

As with the triglycerides, numerous species are possible by various combinations of different head groups and fatty acyl substitution at the first and second positions of the glycerol backbone, fluidity differences are evident as a function of the gel to liquid crystalline transition temperatures. Solubility of phospholipids is intimately linked to the confirmation of the aggregate material rather than strictly a chemical function of the molecule.

Monoacyl phospholipids, which tend to form micelles, are usually more readily soluble in aqueous solutions. It is having solubility in solvents like water, ethanol, chloroform and isopropyl alcohol. PVP gets decomposed at high temperature therefore it is not suitable for preparation of solid dispersions prepared by melt method because melting takes place at a very high temperature. Cyclodextrins: Cyclodextrins are primarily used to enhance solubility, chemical protection, taste masking and improved handling by the conversion of liquids into solids by entrapment.

Methods of preparation of solid dispersions: Various methods used for preparation of solid dispersion system.

These methods are given below.