Is Bactrim (trimethoprim/sulfamethoxazole) effective against strep (Group A beta-hemolytic Streptococcus) infections?

Bactrim (TMP-SMX) Should NOT Be Used for Strep Infections

Trimethoprim-sulfamethoxazole (Bactrim) should NOT be used for Group A beta-hemolytic streptococcal infections as it does not eradicate the organism and will not prevent complications such as rheumatic fever. 1, 2, 3

Evidence Against Using Bactrim for Strep

The evidence against using Bactrim for strep infections is clear and consistent:

• The FDA drug label explicitly states: "The sulfonamides should not be used for treatment of group A β-hemolytic streptococcal infections. In an established infection, they will not eradicate the streptococcus and, therefore, will not prevent sequelae such as rheumatic fever." 2, 3

• Current guidelines from Praxis Medical Insights clearly state that "Trimethoprim-sulfamethoxazole (Bactrim) should NOT be used for streptococcal infections as it does not eradicate Group A Streptococcus in patients with pharyngitis." 1

• Molecular studies have identified factors that cause trimethoprim resistance in Streptococcus pyogenes, including the presence of resistance genes (dfrF, dfrG) and amino acid substitutions in the intrinsic dihydrofolate reductase. 4

Recommended Antibiotics for Strep Infections

For Group A streptococcal infections, the following antibiotics are recommended:

First-line therapy:

• Penicillin remains the drug of choice due to its proven efficacy, safety, narrow spectrum, and low cost 5
• Amoxicillin is often used in place of oral penicillin V, especially for young children, with equal efficacy 5

For penicillin-allergic patients:

• For non-anaphylactic penicillin allergy: Cephalosporins (cephalexin, cefadroxil) 1
• For immediate hypersensitivity to penicillin: Clindamycin or macrolides (azithromycin, clarithromycin) 1

Importance of Proper Strep Treatment

Proper treatment of streptococcal infections is crucial because:

1. Inadequate treatment can lead to serious complications:

   • Acute rheumatic fever
   • Post-streptococcal glomerulonephritis
   • Suppurative complications

2. Treatment failure rates with penicillin have increased over time:

   • Historical failure rates were 5-10% twenty years ago
   • Recent studies show failure rates as high as 20-30% 5

3. A full 10-day course of antibiotics (except for 5-day azithromycin) is required to:

   • Ensure complete eradication of Group A Streptococcus
   • Prevent acute rheumatic fever
   • Reduce risk of treatment failure 1

Clinical Considerations

When treating streptococcal pharyngitis:

• Diagnosis should be confirmed with a throat culture or rapid antigen detection test before initiating antibiotics 1
• The Centor Criteria can guide testing and treatment decisions (tonsillar exudates, tender anterior cervical lymph nodes, lack of cough, fever) 1
• Follow-up throat cultures are indicated only in patients who do not respond clinically to antimicrobial therapy 1

Conclusion on Bactrim for Strep

Despite some evidence that Bactrim may have activity against certain skin and soft tissue infections involving S. aureus 6, the evidence is clear that it should not be used for Group A streptococcal infections. The risk of treatment failure and subsequent complications, particularly rheumatic fever, outweighs any potential benefit of using Bactrim for strep infections.