What is the recommended dosing for doxycycline (antibiotic)?

Doxycycline Dosing

For adults, doxycycline is dosed at 100 mg twice daily (orally or intravenously), with a loading dose of 200 mg on the first day of treatment for most infections. 1

Standard Adult Dosing

• 100 mg twice daily is the maintenance dose for most bacterial infections after the initial loading dose 1
• Loading dose: 200 mg on day 1 (administered as 100 mg every 12 hours), followed by 100 mg daily maintenance dosing 1
• For severe infections (particularly chronic urinary tract infections), continue 100 mg every 12 hours throughout the treatment course 1

Pediatric Dosing (Children ≥8 Years)

• 2.2 mg/kg body weight twice daily for children weighing <100 lbs (45 kg), with a maximum of 100 mg per dose 2, 1
• Loading dose on day 1: 2 mg/lb (4.4 mg/kg) divided into two doses, followed by 1 mg/lb daily as single or divided doses 1
• Children weighing ≥100 lbs should receive standard adult dosing of 100 mg twice daily 3, 1

Condition-Specific Dosing Variations

Tickborne Rickettsial Diseases (RMSF, Ehrlichiosis, Anaplasmosis)

• 100 mg twice daily for adults; 2.2 mg/kg twice daily for children <45 kg 2
• Continue for at least 3 days after fever subsides and until clinical improvement, typically minimum 5-7 days total 2
• For anaplasmosis: extend to 10-14 days if concurrent Lyme disease suspected 2

Community-Acquired Pneumonia (Outpatient)

• 100 mg twice daily for adults without comorbidities 2
• Some experts recommend 200 mg as first dose to achieve adequate serum levels more rapidly 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
• STI post-exposure prophylaxis: 200 mg single dose within 72 hours after sexual exposure (not to exceed 200 mg per 24 hours) 4

Lyme Disease

• Post-exposure prophylaxis: 200 mg single dose for adults; 4 mg/kg (max 200 mg) for children ≥8 years 4
• Early Lyme disease: 100 mg twice daily for 10-21 days 4

Syphilis (Penicillin-Allergic Patients)

• Early syphilis: 100 mg twice daily for 2 weeks 1
• Syphilis >1 year duration: 100 mg twice daily for 4 weeks 1

Malaria Prophylaxis

• Adults: 100 mg daily 1
• Children >8 years: 2 mg/kg daily (up to adult dose) 1
• Begin 1-2 days before travel, continue daily during travel and for 4 weeks after leaving malarious area 1

Inhalational Anthrax (Post-Exposure)

• Adults: 100 mg twice daily for 60 days 1
• Children <100 lbs: 1 mg/lb (2.2 mg/kg) twice daily for 60 days 1

Skin and Soft Tissue Infections (MRSA/MSSA)

• 100 mg twice daily for 7-14 days based on clinical response 4, 3

Route of Administration

• Oral therapy is appropriate for outpatients with early-stage disease who can tolerate oral intake 2
• Intravenous therapy is indicated for severely ill hospitalized patients, particularly those who are vomiting or obtunded 2
• Oral and IV routes provide similar bioavailability 5

Administration Guidelines

• Administer with adequate fluids to reduce risk of esophageal irritation and ulceration 1
• Avoid lying down for 1 hour after taking doxycycline to prevent esophagitis 3
• If gastric irritation occurs, may give with food or milk without significantly affecting absorption 1
• Separate dosing by at least 2 hours from dairy products, antacids, and supplements containing calcium, iron, magnesium, or sodium bicarbonate 3

Critical Safety Considerations

Pediatric Use

• Doxycycline is safe for children ≥8 years for short courses 2
• For life-threatening rickettsial diseases, use in children <8 years when benefits outweigh risks—limited exposure causes negligible tooth staining 2
• Multiple studies demonstrate that short courses in children aged 6-7 years have minimal effect on permanent tooth discoloration 2

Pregnancy

• Generally contraindicated during pregnancy; alternative agents should be considered 4
• May be used for life-threatening infections when benefits outweigh risks 3

Photosensitivity

• Advise patients to avoid sun exposure due to increased risk of photosensitivity reactions 4

Common Pitfalls

• Never delay treatment while awaiting laboratory confirmation for suspected rickettsial diseases—delay can lead to severe disease and death 2
• Do not underdose severe infections—use 100 mg every 12 hours rather than once daily for complicated cases 1
• Fever should subside within 24-48 hours of treatment initiation; if not, consider alternative diagnosis 2
• Renal impairment does not require dose adjustment—doxycycline does not accumulate excessively in renal failure 1