Bacteria Effectively Targeted by Doxycycline
Doxycycline is effective against a broad spectrum of gram-positive and gram-negative bacteria, as well as atypical organisms including Chlamydia, Mycoplasma, Rickettsia, and certain spirochetes. 1
Gram-Positive Bacteria
- Streptococcus pneumoniae (particularly in community-acquired pneumonia) 2
- Bacillus anthracis (anthrax)
- Listeria monocytogenes
- Actinomyces israelii
- Clostridium species
- Propionibacterium acnes (used in acne treatment)
Gram-Negative Bacteria
- Haemophilus influenzae (respiratory tract infections)
- Escherichia coli (when susceptibility testing indicates)
- Klebsiella species (respiratory and urinary tract infections)
- Enterobacter aerogenes
- Shigella species
- Acinetobacter species
- Yersinia pestis (plague)
- Francisella tularensis (tularemia)
- Vibrio cholerae (cholera)
- Campylobacter fetus
- Brucella species (in conjunction with streptomycin)
- Bartonella bacilliformis
- Calymmatobacterium granulomatis (granuloma inguinale)
Sexually Transmitted Infections
- Chlamydia trachomatis (urethral, endocervical, rectal infections) 3
- Ureaplasma urealyticum (non-gonococcal urethritis)
- Treponema pallidum (syphilis, when penicillin is contraindicated)
- Neisseria gonorrhoeae (uncomplicated gonorrhea, when penicillin is contraindicated)
- Haemophilus ducreyi (chancroid)
Other Pathogens
- Rickettsia species (Rocky Mountain spotted fever, typhus fever, Q fever)
- Mycoplasma pneumoniae (respiratory tract infections)
- Borrelia recurrentis (relapsing fever)
- Borrelia burgdorferi (Lyme disease) 3
Clinical Applications
Doxycycline is particularly valuable in treating:
- Respiratory tract infections caused by susceptible organisms 1
- Sexually transmitted infections including chlamydia and as an alternative for syphilis 3
- Tick-borne diseases including Lyme disease and Rocky Mountain spotted fever 3
- Pelvic inflammatory disease (PID) in combination therapy 3
- Malaria prophylaxis against Plasmodium falciparum 1
Important Considerations
Antimicrobial Resistance
- Many strains of Streptococcus pyogenes (up to 44%) and Enterococcus (up to 74%) have shown resistance to tetracyclines 1
- Increasing tetracycline resistance has been observed in Neisseria gonorrhoeae, limiting its use as first-line therapy 3
- Culture and susceptibility testing are recommended before using doxycycline for many gram-negative and some gram-positive infections 1
Pharmacokinetic Advantages
- Doxycycline has excellent oral bioavailability (virtually complete absorption) 4
- Food does not significantly decrease absorption 4
- Long half-life (18-22 hours) allows for once or twice daily dosing 1
- Unlike other tetracyclines, doxycycline does not accumulate in patients with renal insufficiency 4
Contraindications
- Pregnancy and children under 8 years (risk of dental staining and bone growth inhibition) 5
- Photosensitivity reactions can occur, requiring sun protection 5
Doxycycline's broad spectrum of activity makes it a valuable antibiotic for many infections, but its use should be guided by local susceptibility patterns and appropriate antimicrobial stewardship principles to minimize the development of resistance.