Learning Objectives

• Types of coated tablet defects and its causes

Variation in formulation and processing conditions may result in unacceptable quality defects in coated tablets. Some of the defects are as follows:

1. Picking and sticking: Over spraying or excessive film tackiness causes the tablets to stick with each other or to the surface of the pan.On drying a small layer of the polymer film may remain adhered onto the pan or onto another tablet giving a picked appearance on the tablet surface.
2. Roughness: A rough or gritty surface on the coated tablet is a defect observed when the coating is applied by a spray gun. During the process some of the droplets may dry too rapidly before reaching the tablet bed resulting in a spray dried particles instead of finely divided droplets of coating solution.
3. Orange peel: Inadequate spreading of the coating solution before drying or rapid drying of the polymer solution before reaching the tablet bed due to increased temperature fluctuation causes orange peel.
4. Bridging: During drying, the film coat may shrink and it may pull away from the sharp corners resulting in bridging of the surface. This problem is mainly due to defects in formulation of the coating solution.
5. Filling: It is caused by applying or spraying more coating solution than required resulting in a thick film that fills the monogram or bisect.
6. Blistering: During coating when the drying temperature is increased, it leads to the change in the strength, elasticity and adhesion of film, which results in blistering.
7. Bloom/Hazing/Dull film: This can occur due to elevated temperature during the drying of the coated tablets and also if the coated tablets are exposed to high relative humidity.
8. Mottling: This can occur due to improper color selection, processing conditions, non-uniform mixing of the color with the solvent, uneven spray pattern, or over drying during coating procedures.
9. Cracking: It occurs if the internal stress in the film exceeds the tensile strength of the film. Tensile strength of the film can be increased by using high molecular weight polymer blends. The internal strength in the film can be increased by increasing the plasticizer concentration in the formulation.