## 4 Discussion
Non-blister clindamycin tablets showed a significant tendency to increase by a difference between the max-min reflectance in the total spectral range as well as in visible and infrared light. Similarly, day 7 blister tablets with clindamycin had a significantly higher max-min reflectance difference than day 3 blister tablets but only in the visible light range. Thus, the lowest homogeneity was demonstrated for day 7 tablets, as expected. On the contrary, the lowest homogeneity was observed for phenoxymethylpenicillin tablets on day 0 of the experiment. Such discrepancies may result from the presence of particularcoating excipients. A study by [PERSON] et al. [19] analyzed the spectrum of clindamycin using the attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) technique and showed several typical absorption signals corresponding to N-C=O and C-O stretching, as well as S-C-H bending. After incorporating clindamycin into polymer coatings obtained by electrospinning and 3D printing methods, no new functional peaks were found in any of the spectra, which indicated that probably no new chemical bonds were formed between the drug and the polymer mixtures. However, exposure to unfavorable external conditions (UV radiation, temperature, moisture) may affect the formation of new chemical bonds, and in consequence the reflectance values [19]. The assessment of hemispherical directional light reflectance is one of the modern methods of assessing the stability of solid drug forms and is similar to other methods, e.g., the near-infrared hyperspectral images (HIS-NIR) used by [PERSON] et al. [20]. The authors used HIS-NIR to assess the degradation of captopril to captopril disulfide in various layers of captopril tablets with different expiry dates. Based on the results obtained, a model that can predict the expiry date of a medicinal product with an error value of 120 days was developed [20]. This model may be useful for assessing whether a sample shows a degradation pattern consistent with the manufacturer's data or whether there are irregularities in the natural degradation process of the sample. HIS-NIR is widely used in many areas of pharmacy, including monitoring the quality of solid drug dosage forms, detecting counterfeit drugs, assessing the distribution of API in the finished product, and much more. According to the authors [20], the proposed model can predict the degradation rate depending on the expiration date. Similarly, using our proposed methods, reflectance values can distinguish expired and unexpired tablets (THR values are lower for expired tablets) [21], which in turn can be used for rapid screening to improve the efficacy of pharmacotherapy. Spectroscopic analytical methods provide both spatial and spectral data on the sample. This information is becoming increasingly valuable in the chemical imaging of pharmaceutical samples, as it allows the qualitative and quantitative assessment of, among others, the homogeneity of powder samples or particle size and the homogeneity and distribution of API in solid oral dosage forms [22]. In the study by [PERSON] et al. [23], near-infrared chemical imaging (NIR-CI) was used to analyze the spatial distribution of components in tablets. In turn, another study [24] demonstrated that NIR-CI was effective and sensitive in the analysis of the homogeneity of antibiotic content, including ciprofloxacin hydrochloride and maize starch in ciprofloxacin tablets, which was measured inside their blister packages. The authors showed that the blister packages interfered with the shift and background spectra of the raw tablets, which were however successfully removed during the analyses [24]. [PERSON] et al. [25] performed a photodegradation test on three commonly used drugs of finasteride, diclofenac, and naproxen in several ways, i.e., as pure substances dissolved in water, as the solid forms inside the packaging, and also inside and outside the immediate packaging. The test samples were exposed to UV light simulating exposure to sunlight.