Some drugs have no viscosity or low viscosity and need to add other viscous substances to achieve the purpose of granulation. The added viscous substances are called adhesives. While some drugs themselves have viscosity, only need to add appropriate liquid to induce the viscosity of the material. The liquids used to induce the stickiness of drugs are called wetting agents. These liquids and viscous substances that promote granulation by increasing the viscosity of the raw material are called binders.
The binders can be either liquid or fine powder. Usually, the liquid binders were larger and easy to be mixed, while the solid adhesive often acts as both diluent and disintegrating agent. The use of binders should be screened according to the property of drugs, the application and methods of preparation. At the same time, the usage of binders should be appropriate. If the viscosity is insufficient or the amount is too little will cause the tablet fragile. Moreover, if the viscosity is too strong or too much, the tablet will be too hard to disintegrate. The choice of binders needs to be adjusted through practice. Commonly used binders are water, ethanol, starch slurry, saccharides, acacia senegal, gelatin and cellulose derivatives.
Starch slurry: Starch slurry, as the most used adhesive, is a thick colloidal liquid made of starch and water after gelatinized at 70℃ and cooled. The advantage of starch slurry is that it can evenly wet the tablet powder, and it has bonding effect. The disintegration of the tablet made with starch pulp is excellent. As a binder, starch slurry has little adverse effect on drug dissolution. Starch pulp is suitable for stable drugs under hot and humid conditions, which require that the drug is not too loose. The usual concentration is 8%-15%.
Saccharides: Commonly used saccharides binders are syrup, maltose, refined honey and liquid glucose. The viscosity of these substances is very strong, and they are suitable for drugs with poor viscosity. For example, traditional Chinese medicine with strong fiber, or animal tissue drugs with loose texture and greater elasticity.
The commonly used concentration of syrup is 50%-70% (g/g), which is not suitable for acidic or alkaline drugs. Maltose is a thick, light brown liquid that is not suitable as a binder for white tablets. Refined honey is the processed product of honey, often used as binder of traditional Chinese medicine pills. Liquid glucose is an incomplete hydrolytic product of starch, and the commonly used concentrations is 25% and 50%. It has a stabilizing effect on easily oxidized drugs.
Cellulose derivatives: Common cellulose derivatives used as binders are methyl cellulose, carboxymethylcellulose sodium, low-substituted hypromellose, hydroxypropyl methyl cellulose. Either their solution or their dry powder can be used as binders. The usual concentration of cellulose derivative solution is about 5%, and the dosage of pharmaceutical preparations is generally 1%-4%.
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