Is doxycycline (a tetracycline antibiotic) effective for treating streptococcal (strep) infections?

Doxycycline is Not Recommended for Strep Infections

Doxycycline should not be used for streptococcal infections due to high rates of resistance and poor clinical efficacy. 1, 2

Resistance Patterns and FDA Labeling

• The FDA drug label specifically states: "Up to 44 percent of strains of Streptococcus pyogenes and 74 percent of Streptococcus faecalis have been found to be resistant to tetracycline drugs. Therefore, tetracycline should not be used for streptococcal disease unless the organism has been demonstrated to be susceptible." 2

• Resistance rates to tetracyclines among Group A Streptococcus (S. pyogenes) have been documented at 23.8-39.7% for doxycycline and tetracycline respectively. 3

• The FDA label does not list streptococcal infections among the approved indications for doxycycline. 2

Preferred Treatment Options for Strep Infections

• For streptococcal infections, the Infectious Diseases Society of America (IDSA) recommends penicillin as the treatment of choice due to its proven efficacy, safety, narrow spectrum, and low cost. 1

• Alternative first-line options for S. pneumoniae include amoxicillin, macrolides, oral cephalosporins, clindamycin, and respiratory fluoroquinolones. 1

• For penicillin-allergic patients, erythromycin is the recommended alternative for streptococcal infections, not doxycycline. 1

Clinical Evidence Against Doxycycline for Strep

• Doxycycline is bacteriostatic rather than bactericidal against most organisms, which limits its effectiveness in severe infections. 4, 5

• In an ex-vivo pharmacodynamic study comparing antimicrobials against S. pneumoniae, doxycycline failed to prevent bacterial growth at any time point after dosing, while amoxicillin/sulbactam consistently showed bactericidal activity. 5

• While a recent small study suggested comparable clinical failure rates between doxycycline and cephalexin for presumed streptococcal skin infections (6% in each group), this finding is limited to regions with low tetracycline resistance and cannot be generalized. 6

Appropriate Uses of Doxycycline in Infectious Diseases

• Doxycycline is appropriate for:

  • Mycoplasma pneumoniae and Chlamydophila pneumoniae infections 1
  • Community-acquired MRSA skin and soft tissue infections 4, 7
  • Certain respiratory infections caused by susceptible organisms 8

• When coverage for both beta-hemolytic streptococci and CA-MRSA is desired, guidelines recommend either clindamycin alone or doxycycline in combination with a beta-lactam (e.g., amoxicillin). 7

Clinical Pitfalls and Caveats

• Using doxycycline as monotherapy for streptococcal infections may lead to treatment failure due to intrinsic resistance. 1, 3

• Doxycycline should not be used in children under 8 years of age due to the risk of dental staining and enamel hypoplasia. 4, 7

• For mixed infections involving both staphylococci and streptococci, combining doxycycline with a beta-lactam is necessary to ensure adequate coverage of streptococci. 7

• When treating nonpurulent cellulitis (typically caused by beta-hemolytic streptococci), beta-lactam antibiotics should be used as first-line therapy rather than doxycycline. 7