What is the typical dosage and treatment duration for Doxycycline (tetracycline antibiotic) in bacterial infections?

Doxycycline Dosing and Treatment Duration for Bacterial Infections

For most bacterial infections in adults, doxycycline is dosed at 200 mg on day 1 (100 mg every 12 hours), followed by 100 mg daily maintenance, with treatment duration of 7-14 days depending on infection severity and clinical response. 1

Standard Adult Dosing

• Loading dose: 200 mg on first day, administered as 100 mg every 12 hours 1
• Maintenance dose: 100 mg daily (can be given as single dose or divided into 100 mg every 12 hours for severe infections) 1
• Severe infections: 100 mg every 12 hours throughout treatment course, particularly for chronic urinary tract infections 1

Pediatric Dosing (Children >8 Years)

• Children ≤100 pounds: 2 mg/lb divided into two doses on day 1, then 1 mg/lb daily (single or divided doses) on subsequent days 1
• Children >100 pounds: Use adult dosing (200 mg day 1, then 100 mg daily) 1
• Severe infections: Up to 2 mg/lb body weight may be used 1
• Children <8 years: 2.2 mg/kg every 12 hours (not exceeding adult dose) for life-threatening infections only (Rocky Mountain spotted fever, anthrax, ehrlichiosis) 2, 3

Infection-Specific Durations

Skin and Soft Tissue Infections

• MRSA skin infections: 7-14 days based on clinical response 4
• General bacterial skin infections: 7-14 days 4

Sexually Transmitted Infections

• Uncomplicated gonorrhea: 100 mg twice daily for 7 days 1
• Chlamydia (urethral, endocervical, rectal): 100 mg twice daily for 7 days 1
• Nongonococcal urethritis: 100 mg twice daily for 7 days 1
• Early syphilis: 100 mg twice daily for 2 weeks 1
• Late syphilis (>1 year duration): 100 mg twice daily for 4 weeks 1
• Acute epididymo-orchitis: 100 mg twice daily for at least 10 days 1

Streptococcal Infections

• Duration: 10 days 1

Life-Threatening Infections

• Inhalational anthrax: 100 mg twice daily for 60 days (adults and children >100 lb) 5, 1
• Cutaneous anthrax: 100 mg twice daily for 60 days due to simultaneous aerosol exposure risk 5
• Tickborne rickettsial diseases (Rocky Mountain spotted fever, ehrlichiosis, anaplasmosis): Minimum 5-7 days total, continuing at least 3 days after fever resolves 2, 4

Other Specific Infections

• Tularemia, bubonic plague, bacillary angiomatosis: 100 mg twice daily (duration varies by condition) 4
• Malaria prophylaxis: 100 mg daily starting 1-2 days before travel, continuing daily during travel and for 4 weeks after leaving malarious area 1

Special Populations and Considerations

Postexposure Prophylaxis for STIs

• Doxy PEP: 200 mg single dose within 72 hours after sexual exposure (not to exceed 200 mg per 24 hours) 5
• Target population: Gay, bisexual, and other men who have sex with men (MSM) and transgender women with bacterial STI history in past 12 months 5

Renal Impairment

• No dose adjustment required for usual recommended doses 1

Administration Guidelines

• Take with full glass of water and avoid lying down for 1 hour after dosing to prevent esophagitis 5, 1
• May be taken with food or milk if gastric irritation occurs; absorption not significantly affected 1
• Avoid antacids, calcium, magnesium, aluminum, or iron within 2-3 hours of doxycycline administration 4, 3

Critical Safety Considerations

Photosensitivity

• Common adverse effect: Counsel patients to use sun protection and avoid excessive sun exposure 5

Gastrointestinal Effects

• Nausea, vomiting, diarrhea, esophagitis: Take on full stomach with adequate fluid 5, 1

Pregnancy and Lactation

• Generally contraindicated (FDA Pregnancy Category D), but may be used for life-threatening infections when benefits outweigh risks 4, 3
• Short-term use during breastfeeding: Not contraindicated; low levels excreted in breast milk 3

Pediatric Use

• Historical concern about tooth staining: Recent evidence shows short-term doxycycline (<21 days) does NOT cause permanent tooth staining in children <8 years 2, 3
• Use in children <8 years: Appropriate for serious/life-threatening infections (RMSF, anthrax, ehrlichiosis) when benefits outweigh risks 2, 3
• Avoid prolonged or repeated courses in young children 3

Common Pitfalls to Avoid

• Do not exceed 200 mg per 24 hours for doxy PEP to prevent increased side effects 5
• Do not confuse doxycycline with other tetracyclines (tetracycline, minocycline, oxytetracycline), which DO cause permanent tooth staining and remain contraindicated in young children 3
• Do not use cephalosporins or trimethoprim-sulfamethoxazole for anthrax therapy 5
• Do not use penicillin or ampicillin alone for systemic anthrax due to beta-lactamase concerns 5