Antibiotic Selection for Patients with Septic Shock (Review)
Critical Care Clinics
Volume 16, Number 2, April 2000
Antibiotic Selection Based on Sourse of Sepsis:
Skin and Soft Tissue Infections - Toxic Shock Syndrome- Caused by Streptococcus pyogenes (Groups A Beta hemolytic Strep). The Bacteria makes toxins (superantigens) that trigger massive T cell stimulation and cytokine production causing shock and tissue damage. Treatment includes beta-Lactams such as penicillin and cephalothin.
Necrotizing Soft Tissue Infections - May be caused by Clostridium perfringes or Clostridium septicum. These are anaerobic gram positives and can produce secondary infection of ischemic and necrotic tissues and lead to cellulitis, fasciitis, or myositis. Rapid development of local pain, erythema, and swelling with foul smelling purulent drainage and gas formation occurs at the site of recent trauma or surgery. May be hard to distinguish from polymicrobial forms of necrotizing fasciitis. Empiric broad spectrum antibiotics and emergent surgical debridement are required. Use broad spectrum antibiotics such as carbepenem or piperacillin-tozobactam combined with aminoglycoside.
Fresh Water Infections - Usually associated with Aeromonas infection. Trimethoprim-sulfamethoxazole (bactrim), quinolones, third generation cephalosporins, and aminoglycosides are all effective treatments.
Staphylococcus aureus - Common cause of soft tissue and wound infections. May cause stapholycoccal toxic shock syndrome, again a toxin mediated illness (fever, hypotension, desquamating rash, diarrhea, and multiorgan dysfunction). Use antistaphylococcal antibiotics.
Nosocomial Pneumonia-
Pseudomonas aeruginosa is the most feared nosocomial infection in the ICU but other bacteria such as the enteric gram negative bacteria (Enerobacter and Klebsiella) as well as S. aureus are major pathogens to be feared. Up to 50% of nosocomial pneumonias are polymicrobial. Start patient of empiric broad spectrum antibiotics. Selection may be based on the most likely pathogen or known bacterial susceptibility patterns for recent isolates from the specific ICU and hospital. If P.aeruginosa is suspected, combination therapy with antipseudomonal beta-lactam and an aminoglycoside is indicated. In nursing home patients a combination of an extended spectrum cephalosporin with clindamycin or the use of beta-lactam/bata-lactimase inhibitor combination my be a suitable empiric antibiotic choice.
Community-Acquired Pneumonia -
Causes of Community Acquired Pneumonia-
Bacteria - Streptococcus pneumonia, Legionella, Chlamydia pneumoniae, Mycoplasma pnuemoniae, Aerobic gram negative bacteria, Haemophilus species, Klebsiella species, Escherichia coli, Enterobacter species, Pseudomonas aeruginosa, Moraxella catarrhalis, Aspiration pneumonia (polymicrobial anaerobic bacteria).
Viruses - Influenza, Parainfluenza, Adenovirus, Cytomegalovirus, Respiratory Syncitial Virus, Hantavirus.
Fungi - Aspergillosis, Blastomycosis, Cryptocccosis, Histoplasmosis, Coccidiomycossis, Pneumocystis carinii, Mycobacerium tuberculosis.
Streptococcus Pneumoniae is the most common bacterial cause of community acquired pneumonia. Neisseria meningitis and Streptococcus pyogenes are uncommon causes of community acquired pneumonia. Legionella can be a lethal form of pneumonia particularly in patients with advanced age, chronic lung disease, or compromised cell mediated immunity.
Treatment of Community Acquired Pneumonia - Start with broad spectrum antibiotic therapy to cover Pneumococcus, nonpseudomonal gram negative bacteria and Legionella.
A macrolide such as erythromycin or azithromycin and a third generation cephalosporin as cefotaxime, cefriaxone, or ceftizoxime have excellent activity against these pathogens. Quinolones such as levofloxacin and trovafloxacin can be used as monotheraphy. These agents are effective against penicillin resistant pneumococci, aerobic gram negative bacteria, and Legionella. Empiric use of antipseudomonal antibiotics should be considered in certain patients (nursing home residents, patients recently discharged from the hospital, and patients with cystic fibrosis). For HIV patients use Bactrim to cover Pneumocystis carinii and a quinalone or macrolide for bacterial pathogen coverage.
Intra-Abdominal Infection-
Spontaneous Bacterial Peritonitis(SBP) - Occurs in patients with underlying chronic liver disease and ascites. Usually cased by enteric, aerobic gram negative bacteria such E.coli and Kebsiella pneumoniae. Treat with 3rd Generation Cephalosporin.
Peritonitis from Perforation - Polymicrobial (E.coli, Bacteroides fragilis, and enterococci most frequent). Antibiotics include coverage for enteric, aerobic gram negative bacteria and B. fragilis. Monotherapy using carbepenem or piperacillin/tazobactam and duel therapy combining a third generation cephalosporin, a quinalone, or an aminoglycoside with metronidazole is a good start.
Peritonitis in Peritoneal Dialysis Patients - Infection is usually staphylococci (60-80%) . Aerobic gram negative rods account for up to 20% of cases. Emiric therapy with an antistaphylococcal agent (cephalothin) and an aminoglycoside is indicated.
Acute Infection of the Biliary System - Organisms usually are enteric bacteria, with polymicrobial infection being very common. E. coli, Klebsiella, Enterobacter species, and enterococci are common. Anaerobic bacteria such as Bacteroides, and Clostridium can also be isolated. Use same antibiotic approach as used for Peritonitis from Perforation (see above).
Intravenous Catheter Infection - Gram positive cocci usually responsible, but Enterobacter, Pseudomonas, Acinetobacter, and Candida are also frequently involved. Empiric antibiotic therapy with vancomycin and an extended spectrum cephalosporin or aminoglycoside should be initiated after line is removed.
Bacterial Meningitis -
Streptococcus pneumoniae - The leading cause of bacterial meningitis and is associated with the highest case fatality rate. It is the most common cause of bacterial meningitis in adults older than 18 and infants aged 1-23 months.
Neisseria meningitides - The second leading cause of bacterial meningitis and is the most common agent in children 2-18 years old.
Group B Streptococci (Streptococcus agalactiae) and Listeria monocytogenes are responsible for greater than 90% of cases of bacterial meningitis within the first month of life. Liseria may also be found in elderly patients, cancer patients, organ transplant patients, and patients with AIDS.
Haemophilus Influenzae meningitis is a disease of adults or children who have not received the vaccine.
Antibiotics for Meningitis - Empiric antibiotic therapy combining a third generation cephalosporin (ceftriaxone, cefotaxime) and ampicillin is adequate coverage for the majority of community acquired pathogens. In areas where invasive pneumococcal isolates demonstrate high level resistance to penicillin and the prevalence of intermediate or high level resistance to third generation cephalosporins is significant (>5%) or unknown, the empiric use of vancomycin and a third generation cephalosporin should be used.
Genitourinary Tract Infections - E.coli is the most common pathogen causing urinary tract infection the community. Other aerobic gram negatives such as Proteus species and Kebsiella species may also be found. Nosocomial infections of the urinary tract may be caused by antibiotic resistant organisms such as Enterobacter and Pseudomonas aerguginosa. A quinolone combined with an aminoglycoside is reasonable for patients with urinary sepsis.
