Modeling moisture change of packaged dry tablet dosage forms under consumer use condition

A simple mathematical model based on product's moisture sorption isotherm and package's moisture transmission was developed to predict moisture content of dry solid tablets during consumers' use, which is useful for determination of in-use shelf life (ISL) or secondary shelf life. The moisture increase depending on amount of product remaining in the package was accounted for in the mass balance equation on the package. The model was first verified by literature data of desiccant canisters in a plastic bottle of high density polyethylene exposed to two environmental conditions (25 °C and 60% relative humidity (RH); 40 °C and 75% RH) simulating in-use of removing one canister each day. Then an experimental work was conducted on dry refresher candies in a polyethylene terephthalate bottle at 25 °C with two tablets taken out every day, which confirmed the model's capability to predict the product moisture content during in-use storage of 76% and 90% RH. Its use can provide science-based accurate determination of ISL, which may work as consumer guideline. The model is also expected to be helpful for recommending management scheme of whole product life.