In this study, we aimed to calculate dependencies for assessing the value of weight loss during lyophilization of diagnostic preparations depending on the drying temperature and time. A model solution for lyophilization was Hottinger broth with gelatin (1.5%) and peptone (10%) used as stabilizers. To achieve the aim, a full factorial experiment 23 was planned and implemented, the investigated factors in which were the temperature and time of final drying, as well as the amount of substance in the primary packaging. Using ampoules as containers for primary packaging, a regression equation was obtained. The conducted statistical processing of the obtained equation showed the feasibility of the developed mathematical model. According to the model, an increase in the drying temperature and time leads to a decrease in the amount of weight loss; however, weight loss increases under an increase in the amount of substance in the secondary packaging. As a result of the experiments, a correspondence between the experimental and calculated values of weight loss during drying was revealed. The effect of the height of the material under drying on the weight loss was studied when drying an equivalent amount of substance in vials. The developed mathematical model for drying in ampoules was modified to describe the process of lyophilization in vials. The experimental results confirmed the possibility of calculating weight loss during drying using the proposed model. The developed dependencies can be used for estimating the value of weight loss during lyophilization of various substances, which is of particular importance in terms of reducing costs when establishing the temperature and time parameters of drying new biological products and modifying production regimes when changing the amount of product, type of primary packaging or desorption conditions.