Drying kinetics is vital to optimize and predict the moisture content and drying rate when designing drying systems for new drug products. In this work, drying kinetics was studied for naproxen sodium drug formulation dried using microwave radiation by measuring the drug moisture content and drying rate. Ten semi theoretical and empirical thin layer models were tested for their suitability in representing the drying kinetics data at different levels of microwave power. The experimental results showed that the extent of moisture removal increased with increasing microwave power output. It took 35, 24 and 8 minutes to remove 90% of the original moisture content at 30, 60 and 90 W, respectively. The drying rate increased steeply with an increase in time to reach maximum values of 4.7, 6.9 and 11.1 kg/m(2).min at 30, 60, and 90 W, respectively and then decreased to reach a constant value. Among the mathematical models tested, logarithmic model provided the best fit in representing the drying kinetics data for all microwave power values. Two new empirical models developed using experimental moisture content and drying rate data could estimate these two parameters with higher accuracy as a function of drying time and microwave power. (C) 2019 Elsevier B.V. All rights reserved.