LESSON 3
ANTIBIOTICS AND SULFONAMIDES
3-1.
INTRODUCTION
a. Infection is the invasion of the body by a pathogenic organism, the tissue's
reaction to the organism, or the tissue's reaction to a toxin produced by the organism.
An infection occurs when the organism exerts its effect upon the cells or when host
resistance is reduced. Resistance can be reduced if the normal immune process is
compromised or changes occur in the normal makeup of organisms (flora) which give a
harmful organism the opportunity to thrive.
b. The human body has numerous built in barriers against infections.
Mechanical barriers include the skin and mucous membranes. Acids in the stomach
form a chemical barrier that kills bacteria found there. A third natural barrier is the
normal flora existing in the body. There are normally many different types of organisms
growing on the skin and in body cavities all competing with each other for nutrients and
inhibiting the overgrowth of the other organisms. When something happens to disturb
this natural balance (as when an antibiotic kills a large number of bacteria), the
remaining organisms can then flourish and cause a problem. A good example of this is
the overgrowth of yeast, which can occur in the presence of long term antibiotic therapy.
The final barrier is the body's inflammatory process, which is initiated when there is
tissue damage. Mast cells rupture and release histamine, while other mediators cause
vasodilatation and in creased capillary permeability. This allows better access to the
inflamed area by infection fighting cells.
3-2.
ANTI-INFECTIVE AGENTS
An anti-infective or antimicrobial agent is a drug that is used in the treatment or
prevention of infections. These agents are also sometimes referred to as
chemotherapeutic agents, although this term is also commonly applied to drugs used to
treat cancer and really applies to any chemical (drug) used for medical therapy.
Antibiotics and sulfonamides are two examples of these agents. The group of
organisms against which an agent is effective is called its spectrum. Broad-spectrum
antibiotics are effective against a wide range of microorganisms, usually specific
microorganisms in both gram positive and positive organisms only.
a. Bactericidal drugs are those drugs that kill pathogens. This can be
accomplished by one of three methods:
(1)
The drug disrupts cell wall synthesis of bacteria.
(2) The drug acts directly on cell membranes to increase permeability,
leading to leakage of the bacteria's intracellular contents.
MD0808
3-2
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