Impact of Rapid Environmental Changes on Stress Distribution in Tablet Coatings: Simulations

Immediate-release film coatings, also known as "non-functional" film coating, are applied to core tablets to improve product appearance and swallowability, impart taste-masking properties, improve handling and stability of the dosage form, and reduce exposure to active drug substance for caregivers. The coatings have no measurable impact on bio-performance of the drug product but they protect tablets from negative effects of environment such as humidity, oxidation, and light. The mechanical stability and integrity of tablet coatings are therefore important to maintain drug product quality attributes such as appearance and stability. Therefore, environmental conditions under which these coatings may crack are important to understand so as to prevent their occurrence. In this work, we present a novel computational framework to assess the mechanical integrity of tablet coatings exposed to rapid variations in environmental conditions. We perform detailed stress and strain analysis of tablet coatings on tablet surfaces with debossed regions and identify conditions for cracking. Coatings with both elastic and viscoelastic properties are considered. Rapid changes in environmental temperature and humidity can cause differential expansion/contraction of coating and tablet core resulting in stresses that are higher than those experienced during the drying process in a coater. Debossed regions on the tablet surface with sharp surface curvatures act as stress concentrators that nucleate cracks. Small changes in the design of the debossed regions lead to modest reductions in the peak stress. Stress calculations show that coatings that are well bonded to tablet surface can crack only under very extreme conditions.