What is the recommended dosage of doxycycline (tetracycline antibiotic) for an adult patient with no significant medical history and normal renal (kidney function) and hepatic (liver function) for the treatment of a soft tissue infection?

Doxycycline Dosing for Soft Tissue Infections

For an adult with normal renal and hepatic function and a soft tissue infection, doxycycline should be dosed at 100 mg orally twice daily (BID). 1

Standard Dosing Regimen

• Dose: 100 mg orally twice daily 1
• Duration: 7-10 days, depending on clinical response 1
• Route: Can be given orally or intravenously at the same dose 1

When Doxycycline is Appropriate for Soft Tissue Infections

Doxycycline is not a first-line agent for most common soft tissue infections (cellulitis, abscesses). However, it has specific roles:

Recommended Scenarios:

• Purulent cellulitis with suspected MRSA: Doxycycline is a guideline-recommended option when methicillin-resistant Staphylococcus aureus is suspected, particularly in outpatients with purulent drainage 1, 2
• Mild tularemia: 100 mg BID orally is specifically recommended 1
• Bubonic plague: 100 mg BID orally is an alternative to streptomycin 1
• Bacillary angiomatosis: 100 mg BID for 2 weeks to 2 months 1
• Bioterrorism-related cutaneous anthrax: 100 mg BID for 60 days 1

Coverage Profile:

• Good activity against: Eikenella species, staphylococci (including many MRSA strains), and anaerobes 1
• Limited activity: Some streptococci are resistant 1
• Does NOT cover: Beta-hemolytic streptococci reliably 1

Critical Clinical Decision Point

If the infection is non-purulent cellulitis (no drainage, no abscess), doxycycline is NOT appropriate as monotherapy because beta-hemolytic streptococci are the primary pathogens and may be resistant. 1

For non-purulent cellulitis, use:

• Cephalexin 500 mg four times daily, OR
• Cefazolin 1 g IV every 8 hours 1, 3

If you need coverage for both streptococci AND MRSA (purulent cellulitis in areas with high MRSA prevalence):

• Doxycycline 100 mg BID PLUS a beta-lactam (e.g., amoxicillin), OR
• Use clindamycin or linezolid alone 1

Important Contraindications and Caveats

• Do not use in children <8 years of age due to permanent tooth discoloration and decreased bone growth 1, 4
• Avoid in pregnancy (Category D medication) 4
• Not for bite wounds: Use amoxicillin-clavulanate instead, as doxycycline misses important bite-related pathogens 5
• Not for necrotizing infections: These require broad-spectrum IV therapy (vancomycin plus piperacillin-tazobactam or carbapenems) and urgent surgical debridement 1, 5

Treatment Duration and Monitoring

• Standard duration: 7-10 days for most soft tissue infections 1
• Extended therapy: May be needed for specific conditions like bacillary angiomatosis (2 weeks to 2 months) 1
• Clinical response expected: Within 48-72 hours; if no improvement, consider resistant organisms, deeper infection, or alternative diagnosis 5