Basic concept of antibacterial drugs. Anti-infective drugs: various drugs used to treat infections caused by various pathogens (viruses, chlamydia, mycoplasma, rickettsia, bacteria, spirochetes, fungi, protozoa, helminths, etc.). Antibiotics: refers to a class of substances produced by bacteria, fungi or other microorganisms in the course of life that have anti-pathogenic or other activities. Antibacterial drugs: refers to a variety of antibiotics with bactericidal or antibacterial activity, mainly for systemic application (some drugs can also be applied locally) and synthetic antibacterial drugs such as quinolones, nitro-mizoles, sulfonamides, isoniazid and furans. The use of antimicrobial drugs is very widespread and is the most clinically used class of drugs, and the adverse reactions caused by antimicrobials are also more common, so the rational use of antimicrobial drugs is more important for the elderly.