What Doxycycline Treats
Doxycycline is a broad-spectrum tetracycline antibiotic indicated for treating tick-borne diseases (Lyme disease, anaplasmosis, Rocky Mountain spotted fever), sexually transmitted infections (chlamydia, syphilis, gonorrhea), respiratory tract infections (atypical pneumonia), and various other bacterial infections including rickettsial diseases, certain gram-negative infections, and as prophylaxis for malaria and bacterial STIs. 1
Tick-Borne Infections
Doxycycline is the first-line treatment for multiple tick-borne diseases:
Lyme disease: 100 mg twice daily for 10-21 days for early localized or disseminated disease with erythema migrans 2. The 10-day course is sufficient and equally effective as longer durations 2.
Human Granulocytic Anaplasmosis (HGA): 100 mg twice daily for 10 days is the treatment of choice for all symptomatic patients 2. This regimen effectively treats both HGA alone and coinfection with Lyme disease 2.
Rocky Mountain spotted fever and other rickettsial infections: Doxycycline is indicated for all rickettsial diseases including typhus fever, Q fever, and rickettsialpox 1.
Tick bite prophylaxis: A single 200 mg dose within 72 hours of removing an engorged Ixodes scapularis tick can prevent Lyme disease when the tick attachment was ≥36 hours and local infection rates are ≥20% 2. This prophylaxis showed 87% efficacy in preventing erythema migrans 2.
Sexually Transmitted Infections
Doxycycline treats multiple STIs and serves as post-exposure prophylaxis:
Chlamydia: Doxycycline is a recommended first-line treatment for uncomplicated urethral, endocervical, or rectal Chlamydia trachomatis infections 1.
Syphilis: Alternative treatment when penicillin is contraindicated in non-pregnant patients 1.
Gonorrhea: While not currently first-line due to resistance concerns, doxycycline remains effective against many Neisseria gonorrhoeae strains 2.
STI post-exposure prophylaxis (doxy PEP): 200 mg taken within 72 hours after condomless sex significantly reduces bacterial STI acquisition (syphilis, chlamydia, gonorrhea) in men who have sex with men and transgender women who had a bacterial STI diagnosed in the past 12 months 2. This represents a novel prevention strategy with demonstrated efficacy in randomized controlled trials 2.
Lymphogranuloma venereum and nongonococcal urethritis caused by Ureaplasma urealyticum 1.
Respiratory Tract Infections
Doxycycline effectively treats atypical and certain bacterial respiratory infections:
Atypical pneumonia: Indicated for respiratory tract infections caused by Mycoplasma pneumoniae 1.
Community-acquired respiratory infections: Remains an inexpensive alternative with approximately 80% therapeutic success rate 3.
Upper respiratory infections: Effective against Streptococcus pneumoniae when susceptibility testing indicates appropriateness 1.
Infections caused by Haemophilus influenzae and Klebsiella species when bacteriologic testing shows susceptibility 1.
Gram-Negative Bacterial Infections
Doxycycline treats various serious gram-negative infections:
Plague (Yersinia pestis), tularemia (Francisella tularensis), cholera (Vibrio cholerae), and brucellosis (in conjunction with streptomycin) 1.
Chancroid (Haemophilus ducreyi), bartonellosis (Bartonella bacilliformis), and granuloma inguinale (Calymmatobacterium granulomatis) 1.
Campylobacter fetus infections and intestinal infections caused by Yersinia species 4, 1.
Anthrax: Indicated for inhalational anthrax post-exposure prophylaxis to reduce incidence or progression following aerosolized Bacillus anthracis exposure 1.
Other Infections
Additional infectious disease indications include:
Chlamydial infections: Trachoma, psittacosis (ornithosis), and inclusion conjunctivitis caused by various Chlamydia species 1.
Relapsing fever due to Borrelia recurrentis 1.
Listeriosis, Vincent's infection (Fusobacterium fusiforme), actinomycosis (Actinomyces israelii), and clostridial infections when penicillin is contraindicated 1.
Acute intestinal amebiasis: Useful adjunct to amebicides 1.
Malaria Prophylaxis
Doxycycline prevents malaria in specific circumstances:
Indicated for prophylaxis of Plasmodium falciparum malaria in short-term travelers (<4 months) to areas with chloroquine and/or pyrimethamine-sulfadoxine resistant strains 1, 5.
Functions as a partially efficacious causal prophylactic (liver stage) drug and slow-acting blood schizontocidal agent 5.
Non-Infectious Dermatologic Uses
Doxycycline has anti-inflammatory properties beyond antimicrobial effects:
Severe acne: May be useful as adjunctive therapy 1.
Various dermatologic conditions: Anti-inflammatory properties make it suitable for treating hair follicle diseases, granulomatous diseases, and vascular proliferation at doses lower than those effective against infections 6.
Important Contraindications and Precautions
Critical safety considerations include:
Absolutely contraindicated in pregnant women, breastfeeding women, and children <8 years of age due to concerns about tooth development 2. However, recent evidence suggests doxycycline may be safe and effective in young children for Lyme disease when needed, though amoxicillin remains preferred 7.
Photosensitivity: Patients should avoid sun exposure during therapy 2.
Gastrointestinal effects: Take with 8 ounces of fluid to reduce esophageal irritation risk and with food to minimize gastrointestinal intolerance 2, 4.
Severe liver dysfunction is a contraindication 3.