What is the recommended dosage of doxycycline (tetracycline antibiotic) for treating infections?

Doxycycline Dosage Recommendations

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

Standard Adult Dosing

Loading and Maintenance Regimen:

• Initial dose: 200 mg on day 1, administered as 100 mg every 12 hours 1
• Maintenance dose: 100 mg twice daily for subsequent days 1
• For severe infections (particularly chronic urinary tract infections), continue 100 mg every 12 hours throughout treatment 1

Infection-Specific Dosing

Skin and Soft Tissue Infections:

• 100 mg twice daily for 7-14 days for MRSA and MSSA infections 2, 3
• Treatment duration should be based on clinical response 2

Respiratory Tract Infections:

• Community-acquired pneumonia: 100 mg twice daily, with some experts recommending 200 mg as the first dose to achieve adequate serum levels more rapidly 2
• Continue until clinical improvement, typically 7-14 days 2

Tickborne Rickettsial Diseases:

• 100 mg twice daily for at least 3 days after fever subsides and until clinical improvement, minimum 5-7 days total 2
• Fever should subside within 24-48 hours; if not, consider alternative diagnosis 2
• For anaplasmosis with suspected concurrent Lyme disease, extend treatment to 10-14 days 2

Lyme Disease:

• Post-exposure prophylaxis: Single 200 mg dose after high-risk tick bite 4
• Early Lyme disease: 100 mg twice daily for 10-21 days 4

Sexually Transmitted Infections:

• Chlamydia/NGU: 100 mg twice daily for 7 days 1
• Uncomplicated gonorrhea: 100 mg twice daily for 7 days 1
• Early syphilis: 100 mg twice daily for 2 weeks (penicillin-allergic patients) 1
• Late syphilis: 100 mg twice daily for 4 weeks (penicillin-allergic patients) 1
• Doxy-PEP for STI prevention: Single 200 mg dose within 72 hours after sexual exposure (not to exceed 200 mg per 24 hours) 4

Bioterrorism/Severe Infections:

• Inhalational anthrax: 100 mg twice daily for 60 days 2, 1
• Tularemia, bubonic plague, bacillary angiomatosis: 100 mg twice daily 2
• Q fever (acute): 100 mg twice daily for 14 days 4
• Q fever (chronic): 100 mg twice daily plus hydroxychloroquine 200 mg three times daily for ≥18 months 4

Pediatric Dosing

Children >8 years and >45 kg:

• Use adult dosing: 100 mg twice daily 2

Children >8 years and ≤45 kg:

• 2.2 mg/kg every 12 hours (maximum 100 mg per dose) 2
• Alternative: 2 mg/lb on day 1 divided into two doses, then 1 mg/lb daily as single or divided dose 1
• For severe infections: up to 2 mg/lb may be used 1

Children <8 years:

• Generally contraindicated due to dental staining and bone growth effects 2
• May be used for life-threatening infections (e.g., rickettsial diseases) when benefits outweigh risks—limited exposure causes negligible tooth staining 2

Administration Guidelines

Critical Administration Instructions:

• Administer with adequate fluids to reduce esophageal irritation and ulceration risk 1
• Avoid lying down for 1 hour after taking doxycycline to prevent esophagitis 2
• May be given with food or milk if gastric irritation occurs; absorption is not markedly affected 1
• Separate dosing by at least 2 hours from dairy products, antacids, and supplements containing calcium, iron, magnesium, or sodium bicarbonate 2

Special Populations

Renal Impairment:

• No dosage adjustment typically required 3, 1

Pregnancy:

• Generally contraindicated 4
• May be used for life-threatening infections when benefits outweigh risks (e.g., inhalational anthrax) 2

Breastfeeding:

• Use with caution; consider alternative antibiotics if possible 3

Important Clinical Considerations

Common Pitfalls:

• Inadequate treatment duration (<7 days) may lead to treatment failure 3
• Do not delay treatment for suspected rickettsial diseases while awaiting laboratory confirmation—delay can lead to severe disease and death 2
• Complete the full course even if symptoms improve before completion 3

Safety Warnings:

• Avoid sun exposure due to photosensitivity reactions 4
• Monitor for gastrointestinal side effects (occur in approximately 12% of patients) 5
• Therapeutic antibacterial serum activity persists for 24 hours following recommended dosage 1

Route Selection:

• Oral therapy appropriate for outpatients with early-stage disease who can tolerate oral intake 2
• Intravenous therapy indicated for severely ill hospitalized patients, particularly those vomiting or obtunded 2