A Brief Introduction to Non-Functional Excipients

Excipients are the general term for all materials in the prescription except the main active ingredients, such as binders, disintegrants, lubricants, fillers, etc. The choice of excipients for oral solid preparations is affected by factors such as the pharmacological and chemical properties of the raw materials, the preparation process and the price of excipients. There are non-functional excipients and functional excipients. Let’s take a look at the non-functional excipients that are commonly used in solid oral preparations.

Disintegrant

The disintegration of solid oral tablets is very important, because for most solid oral tablets, only after disintegration can the subsequent drug be dissolved and absorbed in the body. In the prescription, the use of natural polymers as disintegrants may cause the viscosity of the surrounding medium to increase due to the partially soluble nature of the polymer, thereby hindering disintegration and dissolution. This problem can be solved by two methods: polymer crosslinking (to reduce the viscosity of the disintegrant) and introducing carboxyl functional groups into the polymer (to increase hydrophilicity).

The mechanism of action of disintegrants includes swelling, gas production, capillary action, and wetting and heat production. The swelling effect requires the disintegrant to have strong water swelling properties to promote the disintegration of the tablet or capsule. Gas production is to allow the disintegrant to generate bubbles through a chemical reaction, thereby using bubbles to promote the disintegration of tablets or capsules, such as adding citric acid or tartaric acid to effervescent tablets. Capillary action means that the disintegrant forms a capillary channel that is easy to wet inside the tablet. After encountering water, the water can quickly enter the inside of the tablet along the capillary to promote disintegration. The effect of moisturizing and heat generation is that some disintegrants will break the chemical bonds when they meet with water, thereby releasing heat and expanding the air remaining in the tablet to promote disintegration.

pH regulator

The pH of the microenvironment can affect the solubility, dissolution, degradation rate and stability of solid preparations. For weakly basic drugs, organic acids are used as acidifiers, such as citric acid, fumaric acid, stearic acid, tartaric acid, etc. At present, citric acid is used more frequently, which can effectively reduce the pH of the microenvironment of the preparation, and has high oral safety and good water solubility, which can reach 1330 mg/ml. For weakly acidic drugs, calcium phosphate, magnesium hydroxide, magnesium oxide, meglumine and sodium carbonate can be used as alkalizing agents.

Fillers and adhesives

The role of filler is to provide a certain volume for the formulation, so that the formulation can be processed into shape. Fillers can be divided into water-soluble fillers and water-insoluble fillers. Commonly used water-soluble fillers include lactose, sucrose, polyethylene glycol, etc., while commonly used water-insoluble fillers are microcrystalline cellulose, calcium hydrogen phosphate, etc.

Adhesives mainly improve the plasticity and bonding strength between particles through intermolecular and interparticle forces, including Van der Waals forces, electrostatic forces, hydrogen bonds, and solid bridges. There are many types of adhesives, such as wet adhesive gelatin, pregelatinized starch, starch, polyethylene glycol, gum arabic, etc. Microcrystalline cellulose, methylcellulose, polyvinylpyrrolidone, and polyethylene glycol are generally used as dry binders.

Lubricant

Lubricants generally occupy a relatively small proportion in the formulation of preparations, and their role is to avoid particle adhesion and sticking and astringency during the process of tableting.

Lubricants generally form a lubricating layer on the surface of the particles, thereby reducing the surface friction between materials and between materials and equipment, and increasing the fluidity of materials. The current types of lubricants mainly include fatty acid metal salts, fatty acids, halogenated hydrocarbons, fatty alcohols, to name just a few here, magnesium stearate, stearic acid, sodium stearyl fumarate, and talc.