What is the coverage and dosage of doxycycline for bacterial infections?

Doxycycline Coverage and Dosing for Bacterial Infections

Doxycycline is a broad-spectrum tetracycline antimicrobial that provides effective coverage against many bacterial pathogens, with standard adult dosing of 100 mg twice daily for most infections. 1

Antimicrobial Coverage

• Doxycycline is effective against a wide range of bacterial pathogens, including:

  • Chlamydia trachomatis (recommended first-line treatment) 2
  • Treponema pallidum (alternative treatment for syphilis in non-pregnant patients with penicillin allergy) 2
  • Many strains of Neisseria gonorrhoeae in the United States, though not recommended as first-line due to increasing resistance 2
  • Rickettsia, Borrelia, and Ehrlichia species (drug of choice) 3
  • Respiratory pathogens causing atypical pneumonia 4
  • Many anaerobic bacteria (superior to older tetracyclines) 5

• Doxycycline has good tissue penetration due to its lipophilic properties, allowing it to reach intracellular pathogens effectively 6

Standard Dosing Regimens

• Adult standard dosing: 100 mg orally twice daily 1
• Initial loading dose: For many infections, 200 mg on the first day (100 mg every 12 hours), followed by 100 mg daily maintenance dose 1
• Pediatric dosing (>8 years old):
  • 2 mg/lb (4.4 mg/kg) divided into two doses on first day
  • 1 mg/lb (2.2 mg/kg) daily thereafter
  • For children >100 lbs, use adult dosing 1

Specific Infection Dosing

• Sexually transmitted infections:

  • Chlamydia: 100 mg orally twice daily for 7 days 2, 1
  • Early syphilis (penicillin allergy): 100 mg orally twice daily for 2 weeks 2, 1
  • Late syphilis (>1 year duration): 100 mg orally twice daily for 4 weeks 1
  • Uncomplicated gonorrhea: 100 mg orally twice daily for 7 days 1

• Skin and soft tissue infections:

  • Purulent cellulitis: 100 mg orally twice daily 2
  • MRSA skin infections: 100 mg orally twice daily 2

• Other infections:

  • Malaria prophylaxis: 100 mg daily 1
  • Inhalational anthrax (post-exposure): 100 mg orally twice daily for 60 days 1
  • Lyme disease: Standard dosing (100 mg twice daily) 4

Pharmacological Considerations

• Doxycycline has a half-life of approximately 12 hours, allowing for convenient twice-daily dosing 2, 4
• Well absorbed orally (75% bioavailability) even with food, unlike some other tetracyclines 3
• Primarily eliminated through hepatic and intestinal routes, making it safe for use in patients with renal impairment 1, 3
• Should be administered with adequate fluids to reduce risk of esophageal irritation 1

Adverse Effects and Precautions

• Most common adverse effects:

  • Photosensitivity (patients should avoid sun exposure) 2
  • Gastrointestinal symptoms including nausea, vomiting 2
  • Esophageal erosion and ulceration (take with plenty of water) 2, 1

• Contraindications:

  • Pregnancy (category D) 2
  • Children under 8 years of age (risk of dental discoloration and bone growth inhibition) 2, 3
  • Severe liver dysfunction 3

• Most adverse effects resolve with discontinuation of the medication 2

Clinical Pearls

• Doxycycline can be taken with food or milk without significantly affecting absorption, which may help reduce gastrointestinal side effects 1
• For severe infections, particularly chronic urinary tract infections, 100 mg every 12 hours is recommended 1
• Bacterial resistance to doxycycline remains relatively low compared to many other antibiotics 3
• When treating STIs, consider the emerging use of doxycycline as post-exposure prophylaxis (200 mg within 72 hours after sexual contact) for high-risk populations 2