Selection of the plasticizer is very critical in coating tablet.
Plasticizer selection depends upon two major criteria :
  1. Glass transition temperature
  2. solubility parameter
For a controlled release dosage form the polymer plasticizer interaction in the latex emulsion must be considered as affecting primarily the drug and substrate and nature of rate limiting system
The type and the concentration of plasticizers actually controls the desired flexibility and permeability in the finished film.

Thus type and concentration of plasticizer can eventually modifies the release rate of the drug from the coated product. Like increasing concentrations of DBS or triethyl citrate decrease the drug release from the Aquacoat coated dosage forms.

Here are some critical aspects for selection of plasticizer
  • The capacity of the plasticizer molecule to modify the polymer-polymer interaction
  • The ability to solvate or solubilize the polymer
  • The ability to add flexibility to the material by reducing its rigid characteristic or brittleness
  • Should have optimum viscosity in the coating solution
  • Should have controlled and desired effect on the film permeability, tackiness, flexibility, solubility, taste, etc
  • Should be nontoxic and compatible with other components
  • Should have desired stability
Optimizing the type of plasticizer and its ration in the formulation depends upon the chemical structure of the polymer, method of application, and the other ingredients present in the system. Recommended concentration of the plasticizers in film coating material is 1-45% weight of the film former