Spectrum of Activity
CLASSIFICATION ACCORDING TO SPECTRUM OF ACTIVITY.
Depending on the range of bacterial species susceptible to these agents, antibacterials are classified as broad-spectrum, intermediate-spectrum, or narrow- spectrum. Note that the spectra of activity may change with acquisition of resistance genes, as will be discussed in the next module.
- Broad spectrum antibacterials are active against both Gram-positive and Gram-negative organisms. Examples include: tetracyclines, phenicols, fluoroquinolones, “third-generation” and “fourth-generation” cephalosporins.
- Narrow spectrum antibacterials have limited activity and are primarily only useful against particular species of microorganisms. For example, glycopeptides and bacitracin are only effective against Gram-positive bacteria, whereas polymixins are usually only effective against Gram negative bacteria. Aminoglycosides and sulfonamides are only effective against aerobic organisms, while nitroimidazoles are generally only effective for anaerobes.
Clinical Implications: Intrinsic Resistance
Knowledge of the intrinsic resistance of a pathogen of concern is
important in practice to avoid inappropriate and ineffective
For bacterial pathogens which are naturally insensitive to a large number of classes of antimicrobials, such as Mycobacterium tuber-culosis and Pseudomonas aeruginosa, this consideration can pose a limitation in the range of options for treatment and thus consequently further increase the risk for emergence of acquired resistance.