Group III includes drugs that do not have an embryotoxic effect – penicillins, cephalosporins, macrolides. These antibiotics can be considered the drugs of choice in the treatment of infectious diseases in pregnant women.
Physiological changes occurring in the body of women during pregnancy have a significant impact on the pharmacokinetics of drugs, including antibiotics. A decrease in the amount of albumin in the blood, an increase in renal clearance, a decrease in absorption from the gastrointestinal tract, and a number of other factors that appear during pregnancy, lead to a decrease in the period of excretion of drugs. The above helps to reduce the concentration of antibacterial substances in the blood and organs compared to non-pregnant ones, this is most pronounced in the third trimester of pregnancy. The individual characteristics of the body, as well as the properties of the drug, have a significant impact on the pharmacokinetics of antibiotics during pregnancy. This is of great diagnostic importance and determines the need for dose adjustment and the mode of administration of the antibiotic.

Often, the content of antibacterial drugs in the blood during gestation exceeds their minimum bacteriostatic concentration for pathogens. However, in some cases, the average therapeutic concentrations of antibiotics in the treatment of infections in pregnant women may be ineffective, and therefore there is a need to increase the dose. Without the risk of pronounced adverse reactions, large doses of antibiotics can be used, having a wide range between therapeutic and toxic effects, such as penicillins, cephalosporins. If the specified range is small, then drugs are prescribed only in the average therapeutic dose. In case of a severe disease, ineffectiveness of the treatment, when there is a need to increase the dose of antibiotics, in order to avoid their embryotoxic action, it is advisable to determine the content of drugs in the blood of pregnant women.