Until the 1920s, most successful anti-infective agents were based on the group-IIB element mercury and the group-VA elements arsenic and antimony. Atoxyl (sodium arsanilate and arsphenamine) was used for sleeping sickness.4 Certain dyes, such as gentian violet and methylene blue, were also found to be somewhat effective, as were a few chemical congeners of the quinine molecule. Some of these agents represented significant achievements in anti-infective therapy, but they also possessed some important limitations. Heavy metal toxicity after treatment with mercury, arsenic, and antimony severely limited the usefulness of agents containing these elements.
Just prior to 1950, great strides were made in anti-infective therapy. The sulfonamides and sulfones (this chapter), more effective phenolic compounds such as hexachlorophene,
Methylene Blue synthetic antimalarial compounds (Chapter 7), and several antibiotics (Chapter 8) were introduced to the therapeutic armamentarium.
Anti-infective agents may be classified according to various schemes. The chemical type of the compound, the biological property, and the therapeutic indication may be used singly or in combination to describe the agents. In this textbook, a combination of these classification schemes is used to organize the anti-infective agents. When several chemically divergent compounds are indicated for a specific disease or group of diseases, the therapeutic classification is used, and the drugs are subclassified according to chemical type. When the information is best unified and presented in a chemical or biological classification system, as for the sul-fonamides or antibacterial antibiotics, then one of these classification systems is used.
This chapter addresses an extremely broad base of anti-infective agents, including the local compounds (alcohols, phenols, oxidizing agents, halogen-containing compounds, cationic surfactants, dyes, and mercurials), preservatives, antifungal agents, synthetic antibacterial drugs, antitubercular and antiprotozoal agents, and anthelmintics. Other chapters in this text are devoted to antibacterial antibiotics (Chapter 8), antiviral agents (Chapter 9), and antineoplastic antibiotics (Chapter 10).
Anti-infective agents that are used locally are called germicides, and within this classification, there are two primary subtypes (see Table 6.1) and several other definitions of sanitization. Antiseptics are compounds that kill (-cidal) or prevent the growth of (-static) microorganisms when applied to living tissue. This caveat of use on living tissue points to the properties that the useful antiseptic must have. The ideal antiseptic must have low-enough toxicity that it can be used directly on skin or wounds; it will exert a rapid and sustained lethal action against microorganisms (the spectrum may be narrow or broad depending on the use). The agent should have a low surface tension so that it will spread into the wound; it should retain activity in the presence of body fluids (including pus), be nonirritating to tis-
TABLE 6.1 Definitions and Standards for Removing Microorganisms
Antisepsis Application of an agent to living tissue for the purpose of preventing infection
Decontamination Destruction or marked reduction in the number or activity of microorganisms Disinfection Chemical or physical treatment that destroys most vegetative microbes or viruses, but not spores, in or on inanimate surfaces Sanitization Reduction of microbial load on an inanimate surface to a level considered acceptable for public health purposes Sterilization A process intended to kill or remove all types of microorganisms, including spores, and usually including viruses with an acceptably low probability of survival Pasteurization A process that kills nonsporulating microorganisms by hot water or steam at 65°C-100°C
sues, be nonallergenic, lack systemic toxicity when applied to skin or mucous membranes, and not interfere with healing. No antiseptic available today meets all of these criteria. A few antibiotics, such as bacitracin, polymyxin, silver sulfadiazine, and neomycin, are poorly absorbed through the skin and mucous membranes and are used topically for the treatment of local infections; they have been found very effective against infections such as these. In general, however, the topical use of antibiotics has been restricted by concern about the development of resistant microbial strains and possible allergic reactions. These problems can reduce the usefulness of these antibiotics for more serious infections.
A disinfectant is an agent that prevents transmission of infection by the destruction of pathogenic microorganisms when applied to inanimate objects. The ideal disinfectant exerts a rapidly lethal action against all potentially pathogenic microorganisms and spores, has good penetrating properties into organic matter, shares compatibility with organic compounds (particularly soaps), is not inactivated by living tissue, is noncorrosive, and is aesthetically pleasing (nonstaining and odorless). Locally acting anti-infective drugs are widely used by the lay public and are prescribed by members of the medical profession (even though the effectiveness of many of the agents has not been established completely). The germicide may be harmful in certain cases (i.e., it may retard healing). Standardized methods for evaluating and comparing the efficacy of germicides have only recently been developed.
Numerous classes of chemically divergent compounds possess local anti-infective properties. Some of these are outlined in Table 6.2.
The most important means of preventing transmission of infectious agents from person to person or from regions of high microbial load, such as the mouth, nose, or gut, to potential sites of infection is simply washing the hands. In fact, one of the breakthroughs in surgical technique in the 1800s was the finding that the incidence of postsurgical infection decreased dramatically if surgeons washed their hands before operating. Regular hand washing is properly done without disinfection to minimize drying, irritation, and sensitiza-tion of the skin. Simple soap and warm water remove bacteria efficiently. Skin disinfectants along with soap and water are usually used as preoperative surgical scrubs and sterilants for surgical incisions.
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