Doxycycline: Uses, Dosage, and Side Effects in Treating Bacterial Infections
Doxycycline is a broad-spectrum tetracycline antibiotic recommended for treating various bacterial infections, with standard adult dosing of 100 mg twice daily for most infections and specific dosing regimens for different conditions. 1
Antimicrobial Coverage and Uses
- Doxycycline is effective against a wide range of pathogens and is recommended as:
- First-line treatment for Chlamydia trachomatis infections 2
- Alternative treatment for syphilis in non-pregnant patients with penicillin allergy 2
- Effective against many strains of Neisseria gonorrhoeae, though not recommended as first-line due to increasing resistance 3
- Treatment for infections caused by Rickettsia, Borrelia, and Ehrlichia 4
- Management of community-acquired respiratory infections and urinary tract infections 4
- Treatment for acne and soft tissue bacterial infections 5
- Prophylaxis for malaria 1
Standard Dosing Regimens
- Adult dosing: 200 mg on the first day (100 mg every 12 hours), followed by a maintenance dose of 100 mg/day 1
- For severe infections: 100 mg every 12 hours is recommended 1
- Pediatric dosing (children >8 years, ≤100 pounds): 2 mg/lb divided into two doses on first day, then 1 mg/lb daily 1
- Children >100 pounds: Use adult dosing 1
Specific Infection Dosing
- Uncomplicated chlamydial infections: 100 mg orally twice daily for 7 days 1
- Nongonococcal urethritis: 100 mg orally twice daily for 7 days 1
- Early syphilis (penicillin allergy): 100 mg orally twice daily for 2 weeks 1
- Late syphilis (>1 year duration): 100 mg orally twice daily for 4 weeks 1
- Uncomplicated gonococcal infections: 100 mg orally twice daily for 7 days 1
- Alternative single-visit dose: 300 mg followed by another 300 mg one hour later 1
- Malaria prophylaxis: 100 mg daily for adults, starting 1-2 days before travel and continuing for 4 weeks after leaving malarious area 1
- Post-exposure prophylaxis for inhalational anthrax: 100 mg orally twice daily for 60 days 1
Doxycycline for STI Prevention (Doxy PEP)
- The CDC recommends doxycycline post-exposure prophylaxis (doxy PEP) for specific high-risk populations:
- Gay, bisexual, and other men who have sex with men (MSM) and transgender women (TGW) with a history of at least one bacterial STI in the past 12 months 3
- Dosage: 200 mg taken within 72 hours after sexual contact (not to exceed 200 mg per 24 hours) 3, 6
- Effectiveness: Reduces syphilis and chlamydia infections by >70% and gonococcal infections by approximately 50% 6
- Should be implemented alongside comprehensive sexual health approaches, including regular STI screening every 3-6 months 3
Pharmacology and Administration
- High bioavailability and tissue penetration due to liposolubility 7
- Long elimination half-life of approximately 12 hours, allowing once or twice daily dosing 3
- Administration with food or milk is recommended if gastric irritation occurs 1
- Adequate fluid intake is recommended to reduce the risk of esophageal irritation and ulceration 1
Adverse Effects and Precautions
- Most common adverse effects include:
- Most adverse effects resolve with discontinuation of the medication 3
- Contraindicated in:
Clinical Considerations
- Long-term use (8+ weeks) is generally safe with primarily minor side effects, though regular monitoring is recommended 8
- Bacterial resistance to doxycycline remains relatively low compared to other antibiotics 4
- Therapeutic success can be expected in approximately 80% of respiratory and urinary tract infections 4
- When used for streptococcal infections, therapy should continue for 10 days 1
- Regular STI screening remains essential for high-risk populations, as doxy PEP does not provide comprehensive protection against all STIs 6