Microcrystalline Cellulose
Properties
It is a white fine crystalline powder, odorless and tasteless, made from free-flowing non-fibrous particles and compressed by its self-adhesion effects. It can be rapidly dispersed in water into the tablet, but insoluble in water, dilute acid or alkali solution, solution and most organic solvents, and can absorb water to swell.
Uses
Anti-caking agents, emulsifiers, binders, disintegrating agents, dispersants, organization modifiers, non-nutrient leavening agents, emulsion stabilizers, thermal stabilizers, carriers for fast drying, finely dispersing agents and tableting agents.
Physical and Chemical Properties
There are many specifications for microcrystalline cellulose, namely, Avicel PH101, PH102, PH103, PH 105, and their differences are the particle size and the moisture content level. Of them, PH 102 has the largest particle, with an average particle diameter of 62μm; while PH 105 has the smallest particle, with an average particle size of 25μm. And PH103 has a less moisture content.
Usage and Dosage
Widely used as the excipient of tablets are two specifications—PH 101 and PH 102, with good compressibility as well as adhesion, flow aid, disintegration and other effects. They are especially suitable for the direct compression process. The compressed tablets have good hardness and are easy to disintegrate. Microcrystalline cellulose presents the plastic deformation during pressurization. Combined with the capillary action, it is easy to draw water inside to destroy the binding force between particles, and to promote the disintegration of tablets.
The price of microcrystalline cellulose is higher than that of more commonly used starch, dextrin, powdered sugar, etc.. Therefore, if not for special needs, it is generally not used as a diluent alone but can be used as the diluting, adhesive and disintegrating agents. It works well as the suspending agents for syrup suspensions, dry syrups, etc.
Possible Problems and Solutions
1. The coefficient of friction of microcrystalline cellulose is low (either static or dynamic). But when the content of drugs or other excipients does not exceed 20%, lubricant is generally not required during tabletting.
2. For the lubricants of alkaline stearic acid salts, if the dosage is higher (more than 0.75%) and the mixing time is longer, then softening phenomena may occur in tablets. However, the case of using PHl02 is better than that of using PHl01.
3. When the water content is more than 3%, during the mixing and tabletting processes, it is easy to produce static electricity, separation and striation phenomena. At this time, the drying method can be used to remove part of the water.
4. When microcrystalline cellulose is used for preparing particles under wet process, due to its water absorption effects, even though the wetting agent is slightly excessive in the amount, still more uniform particles can be obtained without agglomeration.
5. The ratio of microcrystalline cellulose and other excipients has a greater impact on the dissolution rate of insoluble drugs, so pay attention to their ratio.
6. Stability
For the tablets containing more microcrystalline cellulose, in a high humidity environment, since the moisture absorption has affected the hydrogen bonding force between particles, the tablets will gradually get softened. But when these tablets are removed from the high humidity environment, they will resume the hardness.