Comparison of Total Hemispherical Reflectance and Emittance Values Between Metformin Extended-Release Tablets Stored Under Ambient and Stress Conditions

Type 2 diabetes is a serious health problem worldwide. Metformin as the first-line drug in diabetes treatment mainly inhibits glucose production in the liver. Diabetes is often accompanied by other diseases, so patients may take many medications at the same time and have trouble controlling the therapy. This, in turn, may result in medications being stored in different, sometimes random places in the patient’s home where elevated temperatures or long-term exposure to solar radiation are possible. In this study, we aimed to analyze whether the total hemispherical reflectance and emittance values of metformin extended-release tablets would distinguish tablets stored correctly from those stored inconsistently with the manufacturer’s recommendations. Unexpired and expired extended-release tablets containing 750 mg metformin were tested. Unexpired tablets were analyzed in two ways i.e., 15 randomly selected tablets were stored as recommended (day 0), and the 15 next tablets in the blister were stored on a windowsill, where they were exposed to daylight for several hours during the day in mid-spring 2024 for 20 days (day 20). Total hemispherical reflectance (THR) was measured within seven spectral ranges from 335 nm to 2500 nm with a 410-Solar Reflectometer while emittance was analyzed within six spectral infrared ranges from 1500 nm to 21 microns with an ET 100 emissometer. The day 0 tablets showed the highest THR values in five spectral ranges from 400 to 1700 nm compared to expired and day 20 tablets. In the further infrared ranges, from 1.5 to 21 microns, unexpired tablets on day 0 had the lowest reflectance compared to day 20 tablets and expired tablets. This means that a greater amount of IR beam was absorbed by this type of tablet. Therefore, higher emittance was demonstrated by day 0 tablets than by other analyzed tablets. In addition, the emittance values for day 0 tablets decreased with increasing temperature. In conclusion, the storage of metformin extended-release tablets under unfavorable conditions may affect the physical structure of this drug form, which is manifested by changes in the reflectance and directional and hemispherical thermal emittance.