Effectiveness of Trimethoprim-Sulfamethoxazole Against Staphylococcus aureus
Yes, trimethoprim-sulfamethoxazole (TMP-SMX) is effective against Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA), with 95-100% of community-acquired MRSA strains demonstrating in vitro susceptibility. 1
Effectiveness Against Different S. aureus Strains
Methicillin-Susceptible S. aureus (MSSA)
- TMP-SMX is effective against MSSA, though it's not typically the first-line treatment
- For MSSA infections, beta-lactamase stable penicillins (like flucloxacillin) or first/second-generation cephalosporins are preferred 1, 2
- TMP-SMX can be used for MSSA infections in patients with penicillin allergies
Methicillin-Resistant S. aureus (MRSA)
- TMP-SMX is a key treatment option for community-acquired MRSA infections 1
- The Infectious Diseases Society of America recognizes TMP-SMX as an important alternative for MRSA infections 1, 2
- Particularly valuable for outpatient management of MRSA skin and soft tissue infections
Clinical Applications
Skin and Soft Tissue Infections
- TMP-SMX is recommended for outpatient treatment of purulent cellulitis and abscesses likely caused by CA-MRSA 1
- Standard dosing is 160mg/800mg (one double-strength tablet) twice daily for 5-10 days, with treatment duration individualized based on clinical response 1, 3
- Higher doses (320mg/1600mg twice daily) have not shown improved clinical resolution compared to standard dosing 3
Important Limitations
- TMP-SMX should not be used as a single agent for initial treatment of cellulitis due to:
- Possible Group A Streptococcus etiology
- Intrinsic resistance of Group A Streptococcus to TMP-SMX 1
- For severe S. aureus infections, vancomycin has demonstrated superior efficacy compared to TMP-SMX, particularly in bacteremic infections 4
Special Considerations
Patient Populations
- Caution is advised when using TMP-SMX in:
- Elderly patients, particularly those on renin-angiotensin system inhibitors (risk of hyperkalemia)
- Patients with chronic renal insufficiency
- Pregnant women in the third trimester (pregnancy category C/D)
- Infants younger than 2 months of age 1
Treatment Failures
- In cases where TMP-SMX fails to treat uncomplicated MRSA skin infections, minocycline may be an effective alternative 5
- For severe MRSA infections, vancomycin, daptomycin, or linezolid should be considered 1, 2
Resistance Patterns
- While most CA-MRSA strains remain susceptible to TMP-SMX, resistance rates can vary by region and patient population 6
- Higher resistance rates have been observed in:
- Healthcare-associated MRSA strains
- Institutions serving large numbers of HIV-infected patients (due to TMP-SMX use for Pneumocystis prophylaxis) 6
- Regular monitoring of local susceptibility patterns is essential for guiding empiric therapy
In conclusion, TMP-SMX is an effective treatment option for S. aureus infections, particularly for outpatient management of community-acquired MRSA skin and soft tissue infections, though its use should be guided by susceptibility testing and consideration of the specific infection type and severity.