In the mid-50s of the last century, reports began to appear about the ineffectiveness of sulfonamides and antibiotics in bacterial infections. And soon the widespread spread of numerous strains of antibiotic-resistant microorganisms was noted. The fight against drug-resistant bacteria is carried out in several directions: obtaining new chemotherapeutic drugs, chemical modification of known antibiotics, or the use of inhibitors that suppress the activity of bacterial enzymes that inactivate antibiotics. Neocytin is a complex chemotherapeutic drug, which is a solution of tetracycline, levomycitin, novocaine, and ascorbic acid. In this scientific work, some physico-chemical properties of Neocytin are investigated, as well as the main toxicological indicators: acute toxicity, chronic toxicity, the irritating effect of the drug, and the effect of the drug on the mucous membranes. In addition, the effect of the drug on the change in body weight of the studied animals was studied. The drug is a low-toxic agent for warm-blooded animals, both in acute and chronic experiments. Neocytin has mild acute toxicity, without causing severe toxicosis at a dose of 0.3 ml/kg of body weight, and belongs to the 4th hazard class (minor hazardous substances). Long-term use of the drug in doses exceeding therapeutic by 3-5 times does not adversely affect the general condition of animals and other indicators of their clinical status, does not have a harmful local effect, does not adversely affect the main types of metabolism, does not violate the functions and structure of vital systems, organs, and tissues.