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: Continue 100 mg every 12 hours throughout treatment course 1

Infection-Specific Treatment Durations

Skin and Soft Tissue Infections

• MRSA skin infections: 100 mg twice daily for 7-14 days based on clinical response 2
• General bacterial skin infections: 7-14 days duration 2

Sexually Transmitted Infections

• Chlamydia (urethral, endocervical, rectal): 100 mg twice daily for 7 days 1
• Nongonococcal urethritis: 100 mg twice daily for 7 days 1
• Uncomplicated gonorrhea: 100 mg twice daily for 7 days 1
• Acute epididymo-orchitis: 100 mg twice daily for at least 10 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

Life-Threatening Infections

• Inhalational anthrax: 100 mg twice daily for 60 days 3, 2, 1
• Cutaneous anthrax: 100 mg twice daily for 60 days (due to simultaneous aerosol exposure risk) 3, 2
• Tularemia and bubonic plague: 100 mg twice daily, duration varies by clinical response 2

Tickborne Rickettsial Diseases

• Rocky Mountain Spotted Fever, ehrlichiosis, anaplasmosis: Continue at least 3 days after fever resolves, minimum 5-7 days total 4, 2

Postexposure Prophylaxis for STIs

• Doxy PEP: Single 200 mg dose within 72 hours after sexual exposure (maximum 200 mg per 24 hours) 3
• Target population: Gay, bisexual, and other men who have sex with men (MSM) and transgender women with bacterial STI history in past 12 months 3

Pediatric Dosing

Children >100 pounds (>45 kg)

• Use adult dosing: 200 mg day 1 (100 mg every 12 hours), then 100 mg daily maintenance 4, 1

Children ≤100 pounds (≤45 kg) and >8 years

• Day 1: 2 mg/lb body weight divided into 2 doses 1
• Maintenance: 1 mg/lb body weight as single daily dose or divided into 2 doses 1
• Severe infections: Up to 2 mg/lb body weight may be used 1

Children <8 years (when benefits outweigh risks)

• Dosing: 2.2 mg/kg every 12 hours, not to exceed adult dosing 4, 2, 5
• Approved indications: Rocky Mountain Spotted Fever, tickborne rickettsial diseases, anthrax exposure, life-threatening infections 4, 5
• Safety note: Short-term courses (<21 days) do not cause permanent tooth staining 5

Critical Administration Guidelines

Esophageal Protection

• Take with full glass of water or fluid 1
• Avoid lying down for 1 hour after administration to prevent esophagitis 3, 1
• May take with food or milk if gastric irritation occurs; absorption not significantly affected 1

Drug Interactions to Avoid

• Separate by 2-3 hours: Antacids, calcium, magnesium, aluminum, iron supplements, dairy products 2, 5
• These substances significantly impair doxycycline absorption 5

Common Pitfalls and Caveats

Do not exceed 200 mg per 24 hours when using doxy PEP, even with multiple sexual encounters 3

Streptococcal infections require 10 days of therapy to prevent rheumatic fever complications 1

Photosensitivity is common: Counsel patients to use sun protection and avoid excessive UV exposure 3

Renal impairment: No dose adjustment needed; doxycycline is primarily eliminated hepatically and intestinally 1, 6

Pregnancy: Category D; avoid except for life-threatening maternal infections (anthrax, severe rickettsial disease) where benefits outweigh fetal risks 2, 5

Historical tooth staining concerns: Only relevant for prolonged/repeated courses; short-term use (<21 days) in children <8 years is safe for serious infections 5