By: Charles Vesey, RPh, MS

Cellulosic polymers have been extensively used in the film coating of solid dosage forms to prepare oral sustained release formulations. Knowledge and understanding of the process parameters used in the manufacture of the latter is critical to successful product development, scale-up and launch.

While coating organically is still common, aqueous polymer dispersions eliminate the potential hazards and costs associated with organic solvents. However, when compared to organic polymer solutions, film formation from aqueous dispersions is a complex process.

During the coating process, water evaporates and colloidal polymer particles are drawn together, deform, and coalesce into a continuous film, or barrier membrane. Drug release from these dosage forms can be strongly affected by coating process variables, which influence the coalescence of the polymer particles and subsequent film formation. Each process parameter contributes to the final film coat quality and other important response variables, such as coating process efficiency and product agglomeration.

When determining critical process parameters (CPP’s) for any coating process, one must first determine the critical quality attributes (CQA’s) for the final marketed product. For coated multiparticulates, control of CPP should result in a stable drug release pattern over the shelf life of the product. Use of design of experiments (DOE) can assist identification of CPP and help define scale-up protocols to eliminate potential for unwanted surprises.

The necessity of a post-coating thermal treatment should also be evaluated on an individual basis and continually evaluated through the scale-up process. Post-coating thermal treatment (commonly defined as a ‘curing’ step) helps complete the film formation process and eliminate any changes that may occur in film structure during shelf life.

Surelease®, aqueous ethylcellulose dispersion, has been successfully applied on a myriad of manufacturers’ equipment from laboratory scale through production. Colorcon also continues to develop applications data to assist customers in process optimization and minimize any real or perceived need for curing.

About the Author
Charles Vesey, RPh, MS, is a Product Development Manager at Colorcon.

About Colorcon®
Colorcon® is a world leader in the development, supply and technical support of formulated coatings and excipients for the pharmaceutical industry. With Colorcon as their pharmaceutical product development partner, companies produce cost effective, high quality products with superior performance and appearance. To learn more, please visit http://www.colorcon.com/.