Optimization of aqueous-based film coating of tablets performed by a side-vented pan-coating system

The purpose of this research was to characterize the aqueous-based hydroxypropylmethylcellulose (HPMC) film coating of tablets utilizing a laboratory-scale side-vented pan-coating apparatus (Thai coater). The process and apparatus parameters of potential importance with respect to the final film quality were evaluated by using fractional factorial design (2(6-2)IV) and the process was optimized using response surface methodology (central composite design). Rotating speed of the pan was identified as a major parameter with respect to film thickness (weight increase; p < 0.05) and breaking strength (p < 0.05) of the aqueous HPMC film-coated tablets. Increasing the rotating speed from 5 rpm to 10 rpm resulted in a mean relative change of -43.9% and 2.4% of film thickness (weight increase) and breaking strength, respectively. As expected, inlet air temperature significantly affected the moisture content of the final film-coated tablets (p < 0.01) and the film thickness (weight increase; p < 0.05), but the effects on the other responses studied were minimal or negligible. Pneumatic spraying pressure and position of the spray gun (excluding angle of the gun) did not affect the responses studied. The process parameters relevant to a side-vented pan-coating process can be identified (by fractional factorial design) and, consequently, optimized (by central composite design) by using the factorial design approach.