SELECTION OF ANTI MICROBIAL TO TREAT INFECTIOUS DISEASE

Generally anti microbial are used in 2 ways:

Empirical therapy or initial therapy

Definitive therapy or as definitive

EMPIRICAL THERAPY:

Ideally, the selection of antibiotic should be made after proper identification of infecting microorganism and establishing its sensitivity. However, in critically ill patients such delay might prove fatal, thus in such cases empirical therapy becomes inevitable. It means therapy with antibiotics is started prior to identification of microorganism and its sensitivity testing e.g. Meningitis case needs immediate treatment & delay results in death. Initiation of optimal empirical antibiotic therapy requires knowledge of most likely infecting microorganism and susceptibility to antimicrobial. Clinical picture of a patient helps the physician to know the microorganisms most likely to cause infection in the given host.

Gram staining, a fast bacterial identification test can be of much help in narrowing the list of potential pathogens & permit more rational start of antibiotic therapy. However, in the most cases, only identification of morphology of infective microorganism is not enough to reach specific bacterial diagnosis and selection of single narrow spectrum antibiotic may be inappropriate especially when the disease is life threatening.

Thus a broad antibacterial coverage, that mean a combination of antibiotic or a broad-spectrum agent covering infection from both gram negative and Gram positive microorganism should be started as empirical therapy. The following extremely important precautions must not be missed while stating empirical therapy.

“Whenever clinician is faced with initiating therapy on presumptive bacteriological diagnosis, cultures of blood and certain other body fluids/tissues should be taken prior to the initiation of drug therapy.”

DEFINITIVE THERAPY:

Once the infective microorganism and its susceptibility is established, definitive therapy should be initiated to replace empirical therapy. For definitive therapy, the regimen should be changed to more specific antimicrobial agent having low toxicity.