## 4 Discussion  
The quality of the pharmaceutical product is determined by its physical and chemical properties. Our study evaluated the appearance, diameter, thickness, uniformity of weight, dissolution time, moisture content, as well as mechanical strength of effervescent tablets containing magnesium and vitamin B6. We analyzed both the unevpired and expired types of the selected preparation. Unevpired tablets showed longer disintegration time compared to expired tablets, while, as expected, there were no significant differences in the tablets' weight, thickness, diameter as well as hardness. The mean total reflectance of the surface and the inner structure of the effervescent tablets using reflectance analysis and X-ray microtomography, respectively also were evaluated, as we assumed that these methods may help in the rapid assessment of the degradation process. We observed that the mean THR was significantly higher within the ranges of 400-540 nm, 480-600, 590-720, 700-1100, and 1000-1700 for the unevpired effervescent tablets compared to the expired tablets. In addition, we observed significant differences in mean THR between the top and bottom sides of the tablets. In general, the bottom sides of the tablets showed higher reflectance, which may indicate that more physicochemical changes occurred during storage on the top sides and thus more light is transmitted into the tablet. This may be linked to the packaging material. Previously, near-infrared spectroscopy (NIR) was used to determine degradation products [26] or the quality parameters of mucoadhesive bi-layer thin-film composites [27]. However, the use of hemispheric directional reflectance is a relatively new idea, and there is not much data on the topic [16; 17]. Expired effervescent tablets were characterized by a lower density compared to unevpired tablets, which may translate into a specific dissolution time that was significantly shorter for expired tablets. The microstructure of the solid form of the drug affects parameters such as mechanical strength, stability, and disintegration time. This microstructure is characterized by the density, size, and shape of particles, the distribution of excipients and APIs, and the size of pores, fissures, and micro-cracks. Thus, the high porosity of the tablet \begin{table}
\begin{tabular}{c c} \hline \hline
**Type of Tablet** & **Porosity (\%) N = 3, M \(\pm\) SD** \\ \hline Unevpired & 0.0042 \(\pm\) 0.010 \\ Expired & 0.0140 \(\pm\) 0.015 \\ Unespired tablets dried in a vacuum oven at 50 \({}^{\circ}\)C for 24 h & 0.0060 \(\pm\) 0.013 \\ Expired tablets dried in a vacuum oven at 50 \({}^{\circ}\)C for 24 h & 0.0057 \(\pm\) 0.014 \\ \(p\) & **<0.001** \\ \hline \hline \end{tabular}  
* M—mean; SD—standard deviation; \(\blacksquare\)—hours. Significant difference is in bold.  
\end{table} 
Table 4: Mean percentage porosity in the analyzed effervescent tablets. facilitates the penetration of the liquid into the tablet and increases the rate of dissolution. The values of the average pore diameter of the analyzed effervescent tablets were higher for expired tablets than for unexpired ones. The obtained values of the parameters assessed by X-ray computed microtomography were correlated with each other, and we observed that the higher the density, the lower the diameter on average. The Ph. Eur. 10 defines effervescent tablets as compressed tablets that contain, in addition to the medicinal substance(s), mixtures of acids (e.g., citric or tartaric acid) and sodium carbonates and/or bicarbonates [25]. Increasingly, this form provides a source of vitamins and/or minerals or other substances with nutritional or other physiological effects [2; 3]. Earlier, numerous studies presented effervescent tablets as a matrix to obtain medicinal preparations with faster disintegration, higher drug solubilization, and better stability under higher humidity storage conditions.