What is the typical dosage and treatment duration of Doxycycline for bacterial infections?

Doxycycline Dosing for Bacterial Infections

For most bacterial infections in adults, doxycycline should be dosed at 200 mg on the first day (given as 100 mg every 12 hours), followed by 100 mg daily as maintenance therapy, with treatment duration of 7-14 days depending on the specific infection and clinical response. 1

Standard Adult Dosing

• Loading dose: 200 mg on day 1, administered as 100 mg every 12 hours 1
• Maintenance dose: 100 mg daily thereafter, though severe infections (particularly chronic urinary tract infections) warrant 100 mg every 12 hours 1
• Duration: Most bacterial skin and soft tissue infections require 7-14 days of treatment 2

Pediatric Dosing (Children >8 Years)

• Children ≤45 kg (100 lbs): 2.2 mg/kg twice daily, maximum 100 mg per dose 3, 2
• Children >45 kg: Use adult dosing of 100 mg twice daily 2
• Loading dose: 2 mg/lb (4.4 mg/kg) divided into two doses on day 1, followed by 1 mg/lb daily (or divided twice daily) 1
• Severe infections: Up to 2 mg/lb of body weight may be used 1

Infection-Specific Dosing

Sexually Transmitted Infections

• Chlamydia/NGU: 100 mg twice daily for 7 days 1
• Early syphilis (penicillin-allergic): 100 mg twice daily for 2 weeks 1
• Late syphilis (>1 year duration): 100 mg twice daily for 4 weeks 1
• Doxy PEP for STI prevention: Single 200 mg dose within 72 hours after sexual exposure, not exceeding 200 mg per 24 hours 3, 4

Tickborne Rickettsial Diseases

• Adults: 100 mg twice daily (oral or IV) 3
• Children <45 kg: 2.2 mg/kg twice daily (oral or IV), maximum 100 mg per dose 3
• Duration: At least 3 days after fever subsides with clinical improvement; minimum 5-7 days total 3
• Anaplasmosis: Extend to 10 days if concurrent Lyme disease suspected 3

Lyme Disease

• Post-exposure prophylaxis: Single 200 mg dose (adults) or 4 mg/kg up to 200 mg (children ≥8 years) after high-risk tick bite 4
• Early Lyme disease: 100 mg twice daily for 10-21 days 4

Bioterrorism Agents

• Inhalational anthrax: 100 mg twice daily for 60 days (adults); 2.2 mg/kg twice daily for children <45 kg 1
• Tularemia, bubonic plague, bacillary angiomatosis: 100 mg twice daily 2

MRSA Skin Infections

• Dosing: 100 mg twice daily for 7-14 days based on clinical response 2

Critical Administration Considerations

Esophageal protection: Patients must avoid lying down for 1 hour after taking doxycycline to prevent esophagitis 2. Administer with adequate fluid to wash down the medication 1.

Food interactions: While absorption is not markedly affected by food or milk, separate dosing by at least 2 hours from dairy products, antacids, and supplements containing calcium, iron, magnesium, or sodium bicarbonate 2, 1. If gastric irritation occurs, give with food or milk 1.

Important Contraindications and Warnings

• Children <8 years: Generally contraindicated due to dental staining and bone growth effects, though may be used for severe/life-threatening infections (e.g., Rocky Mountain spotted fever, anthrax) when benefits outweigh risks 3, 2, 4
• Pregnancy: Generally contraindicated; alternative agents preferred, though may be considered for life-threatening infections 2, 4
• Photosensitivity: Counsel patients to avoid sun exposure due to increased photosensitivity reactions 4
• Renal impairment: Dose adjustment not required; doxycycline does not accumulate excessively in renal impairment 1

Route of Administration

• Oral therapy: Appropriate for early-stage disease and outpatient treatment 3
• Intravenous therapy: Indicated for severely ill hospitalized patients, particularly those who are vomiting or obtunded 3