Chapter 127. Treatment and Prophylaxis of Bacterial Infections (Part 10)

Status of the HostVarious host factors must be considered in the devising of antibacterial chemotherapy. The hosts antibacterial immune function is of importance, particularly as it relates to opsonophagocytic function. Since the major host defense against acute, overwhelming bacterial infection is the polymorphonuclear leukocyte, patients with neutropenia must be treated aggressively and empirically with bactericidal drugs for suspected infection (Chap. 82). Likewise, patients who have deficient humoral immunity (e.g., those with chronic lymphocytic leukemia and multiple myeloma) and individuals with surgical or functional asplenia (e.g., those with sickle cell disease) should be treated empirically for infections with encapsulated organisms,...
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Chapter 127. Treatment and Prophylaxis of Bacterial Infections (Part 10) Chapter 127. Treatment and Prophylaxis of Bacterial Infections (Part 10) Status of the Host Various host factors must be considered in the devising of antibacterialchemotherapy. The hosts antibacterial immune function is of importance,particularly as it relates to opsonophagocytic function. Since the major hostdefense against acute, overwhelming bacterial infection is the polymorphonuclearleukocyte, patients with neutropenia must be treated aggressively and empiricallywith bactericidal drugs for suspected infection (Chap. 82). Likewise, patients whohave deficient humoral immunity (e.g., those with chronic lymphocytic leukemiaand multiple myeloma) and individuals with surgical or functional asplenia (e.g.,those with sickle cell disease) should be treated empirically for infections withencapsulated organisms, especially the pneumococcus. Pregnancy increases the risk of toxicity of certain antibacterial drugs for themother (e.g., hepatic toxicity of tetracycline), affects drug disposition andpharmacokinetics, and—because of the risk of fetal toxicity—severely limits thechoice of agents for treating infections. Certain antibacterial agents arecontraindicated in pregnancy either because their safety has not been established(categories B and C) or because they are known to be toxic (categories D and X).Table 127-5 summarizes drug safety in pregnancy. Empirical Therapy In many situations, antibacterial therapy is begun before a specific bacterialpathogen has been identified. The choice of agent is guided by the results ofstudies identifying the usual pathogens at that site or in that clinical setting, bypharmacodynamic considerations, and by the resistance profile of the expectedpathogens in a particular hospital or geographic area. Situations in which empiricaltherapy is appropriate include the following: Life-threatening infection. Any suspected bacterial infection in a patientwith a life-threatening illness should be treated presumptively. Therapy is usuallybegun with more than one agent and is later tailored to a specific pathogen if oneis eventually identified. Early therapy with an effective antimicrobial regimen hasconsistently been demonstrated to improve survival rates. Treatment of community-acquired infections. In many situations, it isappropriate to treat non-life-threatening infections without obtaining cultures.These situations include outpatient infections such as community-acquired upperand lower respiratory tract infections, cystitis, cellulitis or local wound infection,urethritis, and prostatitis. However, if any of these infections recurs or fails torespond to initial therapy, every effort should be made to obtain cultures to guidere-treatment Choice of Antibacterial Therapy Infections for which specific antibacterial agents are among the drugs ofchoice are detailed in Table 127-6. No attempt has been made to include all of thepotential situations in which antibacterial agents may be used. A more detaileddiscussion of specific bacteria and infections that they cause can be foundelsewhere in this volume. Table 127-6 Infections for Which Specific Antibacterial Agents Areamong the Drugs of Choice Agent Infections Common Pathogen(s) (Resistance Rate, %)aPenicillin G Syphilis, yaws, Neisseria leptospirosis, groups A meningitidisb and B streptococcal (intermediate,c 15–30; infections, pneumococcal resistant, 0; geographic infections, actinomycosis, variation) oral and periodontal infections, meningococcal Viridans meningitis and streptococci meningococcemia, (intermediate, 15–30; viridans streptococcal resistant, 5–10) endocarditis, clostridial myonecrosis, tetanus, Streptococcus anthrax, rat-bite fever, pneumoniae Pasteurella multocida (intermediate, 23; infections, ...