What is the coverage and typical dosage of doxycycline (antibiotic) for bacterial infections?

Doxycycline Antimicrobial Coverage and Dosing

Antimicrobial Spectrum

Doxycycline provides broad-spectrum coverage against gram-positive cocci, gram-negative bacteria, atypical pathogens, and select intracellular organisms, making it a versatile first-line agent for multiple bacterial infections. 1, 2

Specific Bacterial Coverage:

• Gram-positive organisms: Streptococci, staphylococci (including some MRSA strains when minocycline unavailable), though vancomycin-resistant enterococci are not reliably covered 3, 4

• Gram-negative organisms: Excellent activity demonstrated with 93.1% collective susceptibility across common isolates, including many Enterobacteriaceae and Neisseria gonorrhoeae (though resistance increasing) 4, 5

• Atypical pathogens: Chlamydia trachomatis (first-line agent), Mycoplasma pneumoniae, Mycoplasma genitalium, and other respiratory atypicals 2, 3, 6

• Intracellular organisms: Rickettsia species, Borrelia burgdorferi (Lyme disease), Ehrlichia/Anaplasma phagocytophilum, Coxiella burnetii 7, 3, 8

• Other pathogens: Plasmodium falciparum (malaria prophylaxis/treatment as combination therapy), Bacillus anthracis (anthrax), select protozoa 9, 8

Standard Treatment Dosing by Indication

Sexually Transmitted Infections (Treatment):

• Chlamydia trachomatis: 100 mg orally twice daily for 7 days 2
• Syphilis (penicillin-allergic patients): 100 mg orally twice daily for 14-28 days depending on stage 2
• Pelvic inflammatory disease: 100 mg orally/IV twice daily as part of combination therapy 6

Respiratory Tract Infections:

• Community-acquired pneumonia (atypical): 100 mg orally twice daily for 7-10 days 3, 8
• Acute exacerbations of chronic bronchitis: 100 mg orally twice daily for 5-7 days 8

Tick-Borne Diseases:

• Human granulocytic anaplasmosis (HGA): 100 mg orally or IV twice daily for 10 days in adults; 4 mg/kg/day divided twice daily (max 100 mg/dose) in children ≥8 years 7
• Lyme disease (early localized): 100 mg orally twice daily for 10-21 days 7

Skin and Soft Tissue Infections:

• Animal/human bites: 100 mg orally twice daily for 7-10 days, provides excellent coverage against Pasteurella multocida and Eikenella corrodens 7
• Erysipeloid: 500 mg penicillin preferred, but doxycycline 100 mg twice daily is alternative 7

Multidrug-Resistant Infections:

• MDR gram-negative bacteria: 100 mg IV or orally twice daily, showing 81.3% clinical improvement and 87% microbiologic cure in ventilator-associated pneumonia 5
• Particularly effective against isolates resistant to azithromycin (93.5% susceptibility), amoxicillin (75.9%), and cefuroxime (64.8%) 4

Prophylactic Dosing Regimens

STI Post-Exposure Prophylaxis (Doxy PEP):

For MSM and transgender women with ≥1 bacterial STI in past 12 months: 200 mg single dose within 72 hours after condomless oral, vaginal, or anal sex (maximum 200 mg per 24 hours). 7, 1, 9, 2

• Reduces syphilis and chlamydia by >70%, gonorrhea by ~50% 2
• Take as soon as possible post-exposure, ideally within hours 1, 9
• Evidence insufficient for cisgender women, heterosexual men, transgender men, or nonbinary persons 1
• Reassess need every 3-6 months with concurrent STI screening at all exposure sites 7, 1, 9

Lyme Disease Prevention:

• Single 200 mg dose within 72 hours of tick removal when: adult/nymphal Ixodes scapularis tick attached ≥36 hours AND local tick infection rate with Borrelia burgdorferi ≥20% 1

Malaria Prophylaxis:

• 100 mg orally once daily starting 1-2 days before travel, continuing throughout exposure, and for 4 weeks after leaving malarious area 9

Anthrax Post-Exposure:

• Adults: 100 mg orally twice daily for 60 days 9
• Children <100 lbs: 2.2 mg/kg orally twice daily for 60 days 9
• Children ≥100 lbs: Adult dosing 9

Critical Administration Instructions

Take doxycycline with a full glass of water (≥200 mL) on a full stomach with non-dairy food, and remain upright for at least 1 hour to prevent esophageal ulceration. 7, 1, 9

• Separate from dairy products, antacids, calcium, iron, magnesium, or sodium bicarbonate by at least 2 hours before AND after dosing to prevent chelation and treatment failure 7, 1, 9
• Food does not significantly impair absorption (unlike first-generation tetracyclines), making it more convenient 3
• Long half-life (~12 hours) allows once or twice daily dosing 2, 3

Common Pitfalls and Precautions

Dosing Errors:

• Never exceed 200 mg doxycycline in 24 hours for STI prophylaxis, even with multiple sexual encounters 1, 9
• Do not use in children <8 years except for life-threatening infections (HGA, anthrax) due to dental staining risk 7, 9
• No dose adjustment needed in renal insufficiency, but avoid in severe hepatic dysfunction 3, 8

Side Effects to Counsel:

• Photosensitivity: Recommend sun protection, avoid tanning beds 7, 1, 9
• Esophagitis/esophageal ulceration: Prevented by upright positioning for 1 hour post-dose 7, 1, 9
• Gastrointestinal intolerance: Nausea, vomiting, diarrhea—taking with food mitigates this 7, 2
• Chronic alcohol consumption may reduce serum levels and efficacy 1

Drug Interactions:

• Review all medications including over-the-counter products for interactions 7
• No clinically significant interactions with gender-affirming hormonal therapy 7
• Separate from antacids and supplements as noted above 7, 1, 9

Resistance Considerations:

• Increasing N. gonorrhoeae resistance limits doxycycline as first-line monotherapy for gonorrhea 2
• Potential for antimicrobial resistance development in commensal organisms and other pathogens with prolonged prophylactic use—ongoing surveillance needed 7, 2
• Despite concerns, resistance rates remain relatively low in Germany and other regions for common pathogens 8