Key Clinical Questions
What resistance patterns are associated with major nosocomial pathogens?
When should empiric antibiotic therapy be initiated? When is it permissible to delay empiric antibiotic therapy, if ever?
What impact do pharmacokinetics and pharmacodynamics have on antibiotic choice?
In what circumstances is combination antibiotic therapy appropriate?
What are the major adverse effects of antibiotics?
In this chapter, we will use the terms antibacterial agents and antibiotics interchangeably. The term antibiotic has sometimes been defined as a substance, produced by microbes, that inhibits the growth of other microbes, especially bacteria. More broadly, it is used to characterize any agent with antibacterial properties, whether found in nature or synthesized artificially. Antibiotics are prescribed to approximately one-third of all hospitalized patients, and account for greater than 10% of hospital pharmacy expenditures. Up to one-half of antibiotic orders may be unnecessary, poorly chosen, or dosed incorrectly. Indiscriminant use of broad-spectrum agents is also believed to be a key contributor to emerging worldwide antimicrobial resistance. The estimated additional hospital costs associated with drug-resistant hospital-acquired bacterial infections in the United States is estimated to several billions of dollars. Hospitalists should be familiar with the currently available antibiotics, their penetration into various tissues, their major adverse effects, and their spectrum of activity relative to local patterns of antibacterial resistance. Antimicrobial prescribing should also take into account issues of cost and the potential for the emergence of resistance.
ANTIBIOTIC CATEGORIES AND SPECTRUM OF ACTIVITY
Major categories, subdivisions, and some individual antibacterial agents are summarized in Table 184-1 according to their mode of action, and side effects and drug-drug interactions are listed in Table 184-2. Antibacterial spectrum often overlaps between different antibiotic groups. However, few antibiotics are active against multidrug- or highly resistant bacteria. Thus, the clinician may sometimes have several choices of potentially appropriate antibiotics, but at other times may only have only one, or even none.
TABLE 184-1Categories of Antibacterial Agents, with Spectrum of Activity and Modes of Action ||Download (.pdf) TABLE 184-1 Categories of Antibacterial Agents, with Spectrum of Activity and Modes of Action
|Antibiotic Category ||Subdivisions (Individual Substances) ||Spectrum of Antibacterial Activity |
|Antibiotics acting on bacterial cell wall |
|A. Beta-lactams || || |
|1. Penicillins || |
Naturally occurring (penicillin G, penicillin V)
Penicillinase-resistant antistaphylococcal (methicillin, oxacillin, nafcillin, dicloxacillin)
Aminopenicillins (ampicillin, amoxicillin)
Carboxy-penicillins and ureido-penicillins (ticarcillin, piperacillin)
Gram-positive cocci, excluding staphylococci and most enterococci. Gram-positive rods, including anaerobes. Spirochetes.
Methicillin-susceptible staphylococci (MSS). Gram-positive cocci, but not many enterococci.
All the above plus enterococci, Listeria monocytogenes, Hemophilus influenzae, Moraxella catarrhalis, and some enteric Gram-negative rods.
All the above plus Enterobacter, Klebsiella, Pseudomonas, Acinetobacter species, and anaerobes.
|2. Cephalosporins ||First generation (cefadroxil, cefazolin, cephalexine, cephradine) ||Gram-positive cocci including MSS, excluding enterococci. Some strains of Escherichia coli, Klebsiella, Proteus mirabilis. Not active against indole-positive Proteus and Serratia. |
| ||Second generation (cefamandole, cefaclor, cefprozil, cefuroxime, cefotetan, cefoxitin, loracarbef) ||Similar to first generation, ...|