Common pathogens

Staphylococcus aureus

Penicillin-sensitive S. aureus (incidence < 10%)

  • Drug of choice is penicillin

Penicillin-resistant S. aureus (incidence 90%)

  • Drugs of choice include cloxacillin, cefazolin, cephalexin

Methicillin-resistant S. aureus (MRSA)

  • Incidence < 5% in non-bacteremic, clinically stable patients; 20% in bacteremic patients, including patients who are systemically ill
  • Resistant to all penicillins, cephalosporins, and carbapenems
  • Treatment of choice for infection is vancomycin

MRSA Colonization & Eradication

Patient Selection:

  • The decision to attempt eradication of MRSA in colonized patients must be individualized
  • Not all patients are likely to benefit from decolonization, and some may experience adverse reactions
  • Judicious use of antibiotics, including mupirocin cream, is required in order to avoid development of further MRSA resistance
  • Infection Prevention and Control can be consulted to assist with decisions regarding management of colonized patients
  • Eradication is generally not recommended for patients with:
    • Active infection
    • Treatment with antibiotics
    • Chronic skin lesions or ulcers
    • Indwelling urinary catheter or other medical device

Eradication Regimen:

  • If a decision is made to attempt to eradicate MRSA, the following regimen is recommended:
    • Chlorhexadine 2% washes once daily x 7 days
    • Rifampin 300 mg PO BID x 7 days
    • Doxycycline 100 mg BID OR Co-trimoxazole DS 1 PO BID x 7 days
    • Mupirocin 2% cream applied to the anterior nares TID x 7 days
      Don gloves and place 1 cm (1/2 inch) on the tip of a sterile cotton-tipped applicator and apply in one nostril. Using another sterile applicator, repeat the procedure in other nostril. Nostrils should then be pinched together and released repeatedly for about one minute to ensure even application of cream.

Follow-up Monitoring:

  • Follow-up monitoring consists of repeat cultures obtained 7 days following the last day of administration of any of the above oral or topical treatments

Streptococcus pneumoniae

Penicillin-sensitive S. pneumoniae (≥ 85%)

  • Drug of choice is penicllin

Penicillin-resistant S. pneumoniae

  • Incidence in Canada (2008) is approximately 16%
  • Initial treatment for meningitis due to these organisms is a combination of ceftriaxone plus vancomycin. Vancomycin can be discontinued following confirmation that the organism is sensitive to ceftriaxone.

Enterococcus spp.

A. Susceptibility

Enterococci are intrinsically and predictably resistant to:
  • Cephalosporins
  • Cloxacillin
  • Clindamycin
  • Co-trimoxazole (TMP-SMX)
  • Aminoglycosides
Agents with activity against Enterococcus include:
  • Ampicillin
  • Piperacillin-tazobactam
  • Vancomycin
  • Nitrofurantoin (for UTI only)
Vancomycin-resistant Enterococcus (VRE):
  • Acquired resistance to vancomycin is increasing
  • This may be transferrable to S. aureus
  • Frequency of VRE increases with increased use of vancomcyin

B. Treatment

  1. Urinary Tract Infection
    • Treatment: ampicillin 1 – 2 g IV q6h, or amoxicillin 500 mg PO TID
    • Alternatives: vancomycin 1 g IV q12h, or nitrofurantoin 50 – 100 mg PO QID

  2. Bacteremia (without endocarditis)
    • Patients with enterococcal bacteremia should be assessed for possible endocarditis. If present, treat as recommended below (B, 3)
    • Treatment: ampicillin 2 g IV q6h ± gentamicin 1 mg/kg* IV q8h*
    • Alternative: vancomycin 1 g IV q12h ± gentamicin 1 mg/kg* IV q8h*

  3. Endocarditis
    • Treatment: ampicillin 2 g IV q4h PLUS gentamicin 1 mg/kg IV q8h*
    • Alternative: vancomycin 1 g IV q8h PLUS gentamicin 1 mg/kg IV q8h*

*Low-dose gentamicin is appropriate when used for synergistic effect during combination therapy. Once-daily, high-dose regimens against gram positive cocci such as enterococci are not recommended for synergy.

Pseudomonas aeruginosa

A. Resistance

P. Aeruginosa is intrinsically and predictably resistant to:
  • Penicillin/ampicillin
  • First/second generation cephalosporins
  • Ceftriaxone, cefotaxime
  • Erythromycin
  • Ertapenem
  • Clindamycin
  • Vancomycin
  • Co-trimoxazole (TMP/SMX)

B. Susceptibility

Antimicrobial agents that may be active against P. aeruginosa and may be used to treat infection due to this organism include:
  • Aminoglycosides (tobramycin, amikacin)
  • Piperacillin/tazobactam
  • Ceftazidime
  • Meropenem
  • Ciprofloxacin (incidence of resistance is 30 – 40%)

Note: prescribing of meropenem is restricted to Critical Care Medicine and Infectious Diseases.

C. Treatment

Options include:
  • Ciprofloxacin 750 mg PO q12h or 400 mg IV q8h
  • Ceftazidime 2 g IV q8h
  • Piperacillin/tazobactam 4.5 g IV q6h
  • Tobramycin 7 mg/kg IV q24h
  • Meropenem 500 mg IV q6h

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