General Principles of Antibiotic Therapy
Definition of Antimicrobial Therapy
The term "antimicrobial agent" refers to all chemotherapeutic agents (i.e., drugs) used to
treat (inhibit or kill) any microbial organism regardless of the classification of the organism.
The term "microbial organism" includes any living organism capable of producing an
infectious disease in another biological entity, including human beings. These microbial
agents include bacteria, mycobacteria, viruses and funguses. Other organisms that are
also included in the category of microbes are actinomycetes (nocardia and actinomyces),
chlamydia, mycoplasma organisms (mycoplasma pneumoniae), rickettsia, spirochetes
(treponema pallidum, leptospira, and borrelia), and parasites.
The chemotherapeutic agents that are used to treat these organisms are subclassified into
categories named antibacterial (or antibiotic), antimycobacterial, antiviral, and
They can also be referred to as antirickettsial, antichlamydial, antiparasitic, etc.
Therapeutic Considerations in the Selection of Antimicrobial Agents
There are several points that must be considered in order to make rational therapeutic
decisions regarding the proper use of antimicrobial agents.
1. Must establish whether an infection (defined as the invasion of healthy tissue by
microbial organisms) is present or not. There are no definite signs or symptoms that can
precisely establish the presence of infection in all circumstances.
- Fever may or may not be present. If present, it does not always signify infection.
- Elevation of white count, normally thought to be present during an active infection, may be
absent in many infections.
- Erythema (redness), edema, and increased warmth are signs of inflammation that may
indicate infection, but may also be present in severe inflammatory diseases without the
existence of infection.
- Purulent drainage (pus) usually is a clear sign of infection, but may be present without
infection. Conversely, there are many infections that do not have purulent discharge as part
of their pathophysiology.
- Serologic studies may or may not be positive; many infections do not have serologic
2. Must correctly identify (if possible) the etiologic organism(s) causing the infection.
- Obtaining cultures (preferably before beginning antimicrobial therapy) may be possible
and may identify the presence of certain species of microbes in the area of the infection.
- There are some infections that are classically represented by certain signs and symptoms
that can help to identify the infectious organism.
- Identifying (in the case of bacteria) whether an organism is aerobic or anaerobic is an
essential criterion in drug selection that must be made in order to establish a rational