Doxycycline covers which organisms
Doxycycline is a broad-spectrum tetracycline antibiotic that covers a wide range of organisms including gram-positive and gram-negative bacteria, atypicals, intracellular pathogens, and some parasites.
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doxycycline spectrum of coverage organisms bacteria
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Doxycycline: Spectrum of Coverage
Doxycycline is a second-generation tetracycline with broad-spectrum bacteriostatic activity. It inhibits protein synthesis by binding to the 30S ribosomal subunit, blocking aminoacyl-tRNA attachment.
Gram-Positive Bacteria
| Organism | Notes |
|---|---|
| Staphylococcus aureus (MSSA, some MRSA) | Variable; check susceptibility |
| Streptococcus pneumoniae | Some strains resistant |
| Bacillus anthracis | First-line for cutaneous anthrax |
| Listeria monocytogenes | Alternative agent |
| Actinomyces israelii | Alternative to penicillin |
| Clostridium perfringens | Alternative (not first-line) |
Gram-Negative Bacteria
| Organism | Notes |
|---|---|
| Haemophilus influenzae | Susceptible |
| Brucella spp. | First-line (with rifampin) |
| Vibrio cholerae | First-line |
| Yersinia pestis | Plague (alternative to streptomycin) |
| Francisella tularensis | Tularemia (alternative) |
| Bartonella spp. | Bacillary angiomatosis |
| Helicobacter pylori | Part of some regimens |
| Campylobacter spp. | Alternative agent |
| Klebsiella granulomatis | Granuloma inguinale |
Note: Pseudomonas aeruginosa and Proteus spp. are intrinsically resistant due to chromosomal multidrug efflux pumps.
Intracellular / Atypical Organisms (KEY strength of doxycycline)
| Organism | Disease |
|---|---|
| Chlamydia trachomatis | Chlamydia, PID, LGV - drug of choice |
| Chlamydia pneumoniae | Atypical pneumonia |
| Chlamydia psittaci | Psittacosis |
| Mycoplasma pneumoniae | Atypical ("walking") pneumonia |
| Ureaplasma urealyticum | Urethritis |
| Rickettsia spp. | Rocky Mountain spotted fever, typhus - drug of choice |
| Coxiella burnetii | Q fever - drug of choice |
| Ehrlichia / Anaplasma spp. | Ehrlichiosis / Anaplasmosis - drug of choice |
Spirochetes
| Organism | Disease |
|---|---|
| Borrelia burgdorferi | Lyme disease - first-line |
| Borrelia recurrentis | Relapsing fever - first-line |
| Treponema pallidum | Syphilis (alternative to penicillin) |
| Leptospira spp. | Leptospirosis |
Parasites / Other
| Organism | Notes |
|---|---|
| Plasmodium falciparum | Malaria prophylaxis and treatment (adjunct) |
| Wolbachia (endosymbiont of filarial worms) | Used in filariasis (Wuchereria bancrofti) and onchocerciasis - kills the Wolbachia endosymbiont, leading to worm sterility |
Anaerobes
Some anaerobic activity (e.g., Bacteroides at low rates), but it is not reliable enough for serious anaerobic infections - prefer metronidazole or clindamycin for those.
Memory Aid - Classic Doxycycline Indications
- MRSA skin/soft tissue infections (community-acquired)
- CAP (atypical coverage)
- Lyme disease (early, non-neurological)
- RMSF and all rickettsial diseases
- Chlamydia (STI)
- Anthrax (cutaneous and post-exposure prophylaxis)
- Brucellosis (with rifampin)
- Malaria prophylaxis
- Acne vulgaris (anti-inflammatory + antibacterial)
Sources: Katzung's Basic & Clinical Pharmacology, 16th Ed. | Fitzpatrick's Dermatology | Goodman & Gilman's Pharmacological Basis of Therapeutics | Goldman-Cecil Medicine
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