Doxycycline Antimicrobial Coverage
Doxycycline is a broad-spectrum tetracycline antibiotic that covers intracellular bacteria, atypical pathogens, many sexually transmitted infections, rickettsial diseases, and select gram-positive and gram-negative organisms, though resistance patterns require consideration for optimal use.
Sexually Transmitted Infections
Doxycycline provides excellent coverage for several STIs:
- Chlamydia trachomatis: First-line treatment at 100 mg orally twice daily for 7 days 1, 2
- Treponema pallidum (syphilis): Alternative treatment in non-pregnant patients with penicillin allergy 3, 1, 2
- Neisseria gonorrhoeae: Effective against many US strains but NOT recommended as first-line due to increasing antimicrobial resistance 3, 1
- Ureaplasma urealyticum: Indicated for nongonococcal urethritis 2
- Lymphogranuloma venereum and granuloma inguinale: FDA-approved indications 2
Important caveat: Doxycycline does NOT provide reliable coverage for Mycoplasma genitalium 4
Intracellular and Atypical Pathogens
Doxycycline's lipophilicity allows excellent tissue penetration for intracellular organisms 5:
- Mycoplasma pneumoniae: Respiratory tract infections 2, 6
- Chlamydia psittaci: Psittacosis 2
- Chlamydia trachomatis: Trachoma and inclusion conjunctivitis 2
Rickettsial and Vector-Borne Diseases
Doxycycline is the drug of choice for:
- Rickettsia species: Rocky Mountain spotted fever, typhus fever, Q fever, rickettsialpox, tick fevers 2, 7
- Borrelia recurrentis: Relapsing fever 2, 7
- Ehrlichia species 7
Gram-Negative Coverage
Doxycycline covers multiple gram-negative organisms, though culture and susceptibility testing are recommended due to variable resistance 2:
- Haemophilus ducreyi: Chancroid 2
- Yersinia pestis: Plague 2
- Francisella tularensis: Tularemia 2
- Vibrio cholerae: Cholera 2
- Campylobacter fetus 2
- Brucella species (in conjunction with streptomycin) 2
- Bartonella bacilliformis: Bartonellosis 2
Variable susceptibility (testing required): Escherichia coli, Enterobacter aerogenes, Shigella species, Acinetobacter species, Haemophilus influenzae, Klebsiella species 2, 7
Gram-Positive Coverage
When susceptibility testing confirms appropriate coverage 2:
- Streptococcus pneumoniae: Upper respiratory infections 2
- Bacillus anthracis: Anthrax, including inhalational anthrax post-exposure prophylaxis 2
- Listeria monocytogenes: When penicillin contraindicated 2
- Actinomyces israelii: Actinomycosis 2
- Clostridium species 2
Note: Minocycline (not doxycycline) is preferred for MRSA 6
Other Indications
- Plasmodium falciparum: Malaria prophylaxis for short-term travelers (<4 months) to chloroquine-resistant areas 2, 7
- Entamoeba histolytica: Adjunct in acute intestinal amebiasis 2
- Fusobacterium fusiforme: Vincent's infection 2
- Severe acne: Adjunctive therapy 2
Post-Exposure Prophylaxis (Novel Indication)
The CDC now recommends doxycycline PEP (200 mg within 72 hours after sexual contact) for MSM and transgender women with bacterial STI in past 12 months 3, 1, 4:
- Reduces syphilis and chlamydia by >70% 4
- Reduces gonorrhea by approximately 50% 4
- Does NOT prevent M. genitalium 4
Key Clinical Considerations
Common adverse effects: Photosensitivity, gastrointestinal symptoms, esophageal erosion/ulceration 3, 1, 7
Contraindications: Pregnancy, children under 8 years of age, severe liver dysfunction 1, 7
Pharmacokinetics: 75% oral absorption, long half-life (~12 hours) allowing twice-daily dosing, excellent tissue penetration, no renal dose adjustment needed 3, 5, 6, 7
Resistance patterns: Generally low incidence in many regions, but increasing resistance in gonorrhea necessitates culture-guided therapy for many organisms 2, 7