Tablet Defects in Pharmaceutical Chemistry

Sources of Tablet Defects in Pharmaceutical Chemistry

Moisture
Improper drying
High speed machines
Tools setting problem
Excess use of binders
Lack of proper lubricant selection
Air interaction
Lack of knowledge
Improper training
Abnormal ratio of excipients
Temperature adjustment

Processing problem

Binding
Sticking,
Picking and Filming
Capping
Lamination
Chipping
Mottling
Weight Variation
Poor flow
Hardness variation
Double impression
Cracking

Binding

It is the adhesion of the granules to the die wall and this cause the resistance of the tablet to eject from the die, it is usually due to insufficient lubrication, which produce tablets with rough and vertical score marks on the edges.

Can be improved by:

1. Increasing lubrication.

2. Improving lubricant distribution.

3. Increasing the moisture content of the granulation

Sticking, Picking & Filming (Adhesion of the material to the punch faces)

Sticking (whole adhesion) is usually due to improperly dried or lubricated granulation causing the whole tablet surface to stick to the punch faces → dull, scratched, or rough tablet faces.
Picking (localized adhesion) is a form of sticking in which a small portion of granulation sticks to the punch face & a portion of the tablet surface is missed.
Filming is a slow form of sticking and is largely due to excess moisture in the granulation

Capping & Laminating

Ø Capping occurs when the upper segment of the tablet separates from the main portion of the tablet & comes off as a cap.

Most annoying problem
Can appear immediately after compression, or hours, even days after preparation.
It is usually due to air entrapped in the granulation which is compressed in the die during the compression & then expands when the pressure is released.

Reasons of capping :

Large amount of fine particles in the granulation &/or the lack of sufficient clearance between the punch and the die wall.
In new punches and dies that are tight fitting.
Too dry granules.

Lamination is due to the same causes as capping except that the tablet splits at the sides into two or more parts.

If tablets laminate only at certain stations, the tooling is usually the cause.

Solutions for capping & laminating

Increasing the binder.
Adding dry binder such as gum acacia polyvinylpyrrolidone (PVP).
Decreasing the upper punch diameter.
By maintaining certain degree of moisture in the granules using hygroscopic materials like methyl cellulose, sorbitol, polyethylene glycol etc.

Mottling

−Unequal distribution of color on the tablet surface with light and dark areas standing out in an otherwise uniform colored surface

Causes :

Variation in the colors of ingredients (drug and other additives)
Drugs with degradation nature and have different colored degraded products
Migration of dye to the surface of granulation during drying. At high temperature dyes are easily migrate to surface and spread to upper surface.
Uneven distribution of colored adhesive gel solutions resulting in precipitation
The improper size either large or small particles enhances color distribution. During preparation, dyes are not properly mixed and not selected ideally or any incompatibility will tends to enhance appearance of color on tablet surface.
Improper storage conditions.

Remedy:

By using bright coloring agent that will mask all the color variations of the ingredients
Proper drying by reducing the drying temperature
Colored adhesive gel solutions must be added when they are hot.
It is better to incorporate fine powder adhesives like acacia and tragacanth into product before adding the granulating fluid
By changing the solvent system or binder system
Grinding to small particle size.