Antimicrobials narrow-spectrum

Empirical selection of antimicrobial spectrum of activity should be related to the severity of the illness. Generally, acutely ill patients may require broader-spectrum antimicrobial coverage, whereas less ill patients may be managed initially with narrow-spectrum therapy. While a detailed description of antimicrobial pathogen- specific spectrum of activity is beyond the scope of this chapter, this information can be obtained readily from a number of sources.9,10... 

Spectrum of activity A qualitative term that describes the number of different bacterial species that are susceptible to an antimicrobial regimen. Generally, broad-spectrum activity refers to regimens that possess activity against many bacterial species, whereas narrow-spectrum therapy refers to activity against a few bacterial species. 

B. Isoniazid, a narrow-spectrum antimicrobial agent. C. Tetracycline, a broad-spectrum antimicrobial agent. 

Subgroups and Antimicrobial Activity Beta-Lactamase-Susceptible and Narrow Spectrum... 

Very narrow spectrum, penicillinase-resistant drugs This subclass of penicillins includes methicillin (the prototype), nafcillin, and oxacillin. Their primary use is in the treatment of known or suspected staphylococcal infections. Methicillin-resistant staphylococci (MRSA) are resistant to other members of this subgroup and may be resistant to multiple antimicrobial drugs. 

Narrow spectrum The range of activity of an antimicrobial agent that attacks only a few kinds of micro-organisms. 

Rea, M.C., Dobson, A., O Sullivan, O., et al. (2011b). Effect of broad- and narrow-spectrum antimicrobials on Clostridium difficile and microbial diversity in a model of the distal colon. Proc Natl Acad Sci USA 108 Suppl 1, 4639-4644. 

Empirical selection of antimicrobial therapy for ventilator-associated, health care-associated, and hospital-associated pneumonia is broad spectrum however, once culture and susceptibility information are available, the therapy should be narrowed (deescalation) to cover the identified pathogen(s). 

What antimicrobials will cover these organisms and not be too broad or narrow in spectrum, will penetrate into the site of infection, and what they cost... 

Antimicrobial therapy is the cornerstone of treatment in UTIs. This therapy should ideally be well tolerated, narrow in antimicrobial spectrum, lend itself to patient compliance (taken as infrequently as possible), have adequate concentrations at the site of the infection, and have good oral bioavailability. Table 76-2 reviews antibiotics frequently used to treat UTIs with comments on their use, and Table 76-3 reviews frequency, duration, and doses of those antibiotics. 

Benzylpenicillin or penicillin G has a narrow antimicrobial spectrum. It is active with respect to Gram-positive bacteria (staphylococcus, streptococcus, and pneumococci), causative agent of diphtheria, and anthrax bacillus. Gram-negative bacteria are resistant to it. Benzylpenicillin is broken down by stomach acid and destroyed by staphylococcus penicillinase. 

The monobactams, of which aztreonam [az TREE oh nam] is the only commercially available example, are unique because the p-lac-tam ring is not fused to another ring (Figure 30.9). Monobactams also disrupt cell wall synthesis. The drug s narrow antimicrobial spectrum precludes its use alone in empiric therapy (p. 279). Aztreonam is resistant to the action of p-lactamases. 

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