## 4 Discussion  
Photostability is an increasingly discussed topic, especially in relation to specific parameters of finished products that can be improved to provide greater protection against solar radiation [12; 13]. In the field of photostability, there is a constant search for rapid, non-invasive, and ecological techniques for drug analysis. The present study evaluated parameters that are relatively rarely analyzed in pharmaceutical preparations, i.e., hemispherical directional reflectance and homogeneity, for which measurements were performed using portable devices. The advantage of these types of equipment is the possibility of monitoring drugs in almost any condition and at any stage of the distribution chain [1]. In this study, we used antibiotic tablets, because these APIs are generally considered sensitive to stress conditions (solar radiation, temperature, and moisture), but to a different extent depending on the type of antibiotic. Data indicate that the time of degradation of ciprofloxacin and sulfamethoxazole under simulated solar radiation is relatively fast (half-lives of 0.5 and 1.5 h, respectively) but in roxithromycin and erythromycin, macrolides are persistent in such conditions (half-life of 2.4-10 days) [14]. We confirmed the differences in THR values between antibiotic tablets before, during, and after UV irradiation within seven analyzed spectral ranges. For the borderline spectral ranges measured by the reflectometer, the lowest THR on day 0 amounting to about 35% and 46% was found for the 335-380 nm and 1700-2500 nm bands, respectively. Therefore, about 65% and 55% of radiation in these ranges can interact with the tested pharmaceutical formulation. Understanding this subject, one can influence the increase in protection against ultraviolet and infrared wavelengths, and, in particular, this radiation should be blocked by designed drug packaging. In our recent preliminary study on reflectance analysis of pharmaceutical packaging, we have shown that blisters and white areas of cefuroxime packaging provide better protection from radiation than colored areas of the packaging [15]. In the present study, we also demonstrated the changes in the homogeneity of tablets which was assessed based on hyperspectral analyses. For the clindamycin tablets evaluated in this study, the THR tended to decrease after UV exposure compared to tablets at the beginning of this study. In contrast, the THR values increased after UV exposure for the tablets containing penicillin V. This is most likely related to the complexity of the concept of photostability. The study by [PERSON] et al. [16] pointed out how light can affect a medicinal preparation. A change in the active substance as well as degradation of the excipient polymers can occur in this process. The literature data showed that excipients used in drug preparations play an important role relating to drug stability [17; 18]. They can provide suitable conditions to protect the drug substance from degradation, e.g., under the influence of moisture [17]. It is therefore appropriate to consider the impact of adverse conditions on the full composition of the medicinal product and not just the active substance. Thus, it is important to know and understand the nature and characteristics of a given excipient and, in particular, its impact on the shelf life of the finished drug. This knowledge is essential for the correct design and manufacture of the drug. The use of excipients always involves an additional risk of impurities that may affect subsequent stability, but it was noted that impurities that are problematic in one case may not be relevant for another preparation [18]. We assume that the differences obtained in our study may result from the various ingredients used in the preparation process. In addition, based on the hyperspectral analysis, we observed changes in the homogeneity of the tablets over time with UV exposure.