Antibiotics are a group of drugs which are used in treatment of bacterial infections. Bacteria are live microorganisms which having got into a human body, begin active activity and reproduction. The effect of antibacterial therapy consists in direct destruction of the activator and also delay of reproduction of causative organisms. Due to these antibacterial drugs are divided into 2 big groups: bactericidal – destroying a bacterium and also bacteriostatic, suppressing their growth. Besides, antibiotics possess narrow and a broad spectrum of activity. Drugs of a narrow action spectrum destroy an infection selectively while drugs of a wide range destroy the most part of microorganisms including those which bring benefit to the person. What antibiotics to accept for treatment of various diseases the doctor after diagnosis has to solve. To take such drugs on the discretion it is fraught with complications.