Antibiotic Choice for Coagulase-Negative Staphylococci in Urine
For coagulase-negative staphylococci (CoNS) isolated from urine, vancomycin is the preferred antibiotic for methicillin-resistant strains, while cefazolin or a first-generation cephalosporin is appropriate for methicillin-susceptible strains.
Treatment Approach Based on Methicillin Susceptibility
Methicillin-Resistant CoNS
- Vancomycin is the treatment of choice for methicillin-resistant CoNS, which are common in nosocomial settings 1
- Dosing: 1 g IV every 12 hours for adults 1
- CoNS causing healthcare-associated infections are typically methicillin-resistant, particularly when infection develops within 1 year after surgery or in hospitalized patients 1
- Vancomycin demonstrates 100% susceptibility against CoNS in multiple studies 2
Methicillin-Susceptible CoNS
- Cefazolin (1 g IV every 8 hours) is the preferred agent for methicillin-susceptible CoNS 1
- Alternative options include other first-generation cephalosporins or penicillinase-resistant penicillins 1, 3
- Cefotaxime also demonstrates excellent activity with 100% susceptibility 2
Alternative Oral Options for Uncomplicated Cases
When oral therapy is appropriate for uncomplicated urinary CoNS infections:
- Fluoroquinolones (ciprofloxacin 500 mg PO every 12 hours or levofloxacin 500 mg PO daily) show approximately 90% susceptibility 1, 2, 4
- Trimethoprim-sulfamethoxazole (1 double-strength tablet PO every 12 hours) can be used, though resistance rates vary (23-77% in some studies) 1, 2, 5
- Clindamycin shows good activity with approximately 84-90% susceptibility 2, 5
Critical Clinical Considerations
Determining Clinical Significance
- CoNS in urine often represents contamination rather than true infection, particularly in catheterized patients 1
- Urine cultures have very low specificity for diagnosing UTI in patients with indwelling catheters, though negative urinalysis effectively rules out infection 1
- Treatment should only be initiated when there are clear signs of infection (fever, dysuria, systemic symptoms) rather than asymptomatic bacteriuria 1
Duration of Therapy
- For uncomplicated CoNS infections with catheter removal: 5-7 days 1
- If catheter retained: 10-14 days with consideration of antibiotic lock therapy 1
- For upper urinary tract involvement, longer courses may be warranted 1
Common Pitfalls to Avoid
- Do not treat asymptomatic bacteriuria with CoNS in catheterized patients, as bacteriuria is nearly universal and does not indicate infection 1
- Avoid empiric use of broad-spectrum agents like carbapenems unless there are specific risk factors for multidrug resistance 1
- Do not use rifampin as monotherapy due to rapid resistance development 1
- Recognize that S. lugdunensis, though coagulase-negative, behaves like S. aureus and requires more aggressive treatment similar to methicillin-susceptible S. aureus 1
Resistance Patterns
CoNS demonstrate high resistance rates to:
- Penicillin G (>70%) 6, 5
- Oxacillin (42-70% depending on species) 4, 5
- Erythromycin (58%) 5
- Tetracycline (65%) 2
CoNS maintain excellent susceptibility to: