ABSTRACT Research objective: to conduct a quantitative determination of sodium diclofenac and vitamin B-12 in new lyophilic drug Cobafen using modern physicochemical methods of analysis. Materials and methods. During the research we used the samples of commercially available substances of mecobalamin chloride produced by Apex Medichem Ltd. (India), D-mannitol manufactured by Shandong Tianli Pharm. Co. Ltd. (China) and polyvinyl pyrrolidone (PVP) produced by Merck (Germany), as well as chemical reagents by SigmaAldrich (USA) and Hi-Media (India). For spectrophotometry analysis we applied a UV1800 double-beam spectrophotometer (Shimadzu, Japan) and Agilent 8453E single-beam spectrophotometer (Agilent Technologies, Germany). Besides, the study was carried out under conditions of reverse phase HPLC (Agilent 1280 gradient HPLC chromatograph (Agilent Technologies, USA) and LC-20 (Shimadzu, Japan)). Results. Conducted 5 independent experiments for each formulation and each freezing mode showed that D-mannitol is the additive agent of choice. Besides, lyophilizates produced using D-mannitol corresponded to the indicated quality attribute. When analyzing mecobalamin by HPLC, it was established that the method of choice was PP with methanol: buffer solution (26.5:73.5), the optimal concentration in the analysis of mecobalamin is 2 mg / ml. Conclusion. It was established that sharp freezing condition is the most preferred due to the saving in production cycle time. The proposed HPLC method for quantitative determination of the active substance in the drug, validated by all validation parameters, is included in the pharmacopoeial monographs of JURABEK LABORATORIES JV LLC.