Final answer:
Broad spectrum antimicrobial agents should be used in serious systemic infections without known causes, for failed narrow-spectrum treatment, or against multiple microbes. They pose a risk of superinfection and disrupting normal microbiota. Narrow-spectrum agents are typically preferred to prevent superinfection and resistance.
Step-by-step explanation:
The appropriate time to use a broad spectrum agent is in several specific clinical situations. For instance, broad spectrum antimicrobials are warranted for serious systemic infections when there is no time to determine the causative agent.
They are also used when narrow-spectrum antimicrobials fail or for the treatment or prevention of infections that involve multiple types of microbes. Broad spectrum agents are useful as empiric therapy while awaiting laboratory identification of the infecting pathogen, treatment of polymicrobic infections, or as a prophylactic measure in surgery and invasive procedures.
However, there is a risk associated with their use because they may disrupt the normal microbiota and increase the risk of a superinfection, such as candidiasis or pseudomembranous colitis caused by Clostridium difficile.
Use of narrow-spectrum antimicrobial drugs is often preferred to avoid superinfection and the development of antimicrobial resistance. When selecting an antimicrobial drug, factors such as bacteriostatic versus bactericidal mechanisms, spectrum of activity, dosage and route of administration, potential side effects, and interactions with other drugs must be considered.
The development of a superinfection is more likely to occur with long-term use of broad-spectrum antimicrobials rather than narrow-spectrum ones or short-term use of either type.