What is the recommended dose and frequency of doxycycline (antibiotic) for treating bacterial infections?

Doxycycline Dosage and Frequency for Bacterial Infections

For most bacterial infections in adults, doxycycline should be administered at 100 mg twice daily (every 12 hours), with an initial loading dose of 200 mg on the first day of treatment. 1

Standard Dosing Regimens

Adults:

• Initial dose: 200 mg on first day (100 mg every 12 hours)
• Maintenance dose: 100 mg daily as a single dose or 100 mg every 12 hours for more severe infections 1
• Duration: Typically 7-14 days depending on infection type 2

Children (>8 years of age):

• Initial dose: 2 mg/lb (4.4 mg/kg) of body weight divided into two doses on first day
• Maintenance dose: 1 mg/lb (2.2 mg/kg) of body weight daily as a single dose or divided into two doses
• For severe infections: Up to 2 mg/lb (4.4 mg/kg) of body weight daily 1
• Not recommended for children under 8 years due to risk of dental staining and enamel hypoplasia 3

Specific Infection Dosing

Skin and Soft Tissue Infections (SSTI):

• Outpatient MRSA SSTI: 100 mg twice daily for 5-10 days 2

Sexually Transmitted Infections:

• Chlamydia/Nongonococcal urethritis: 100 mg twice daily for 7 days 3, 1
• Syphilis (early): 100 mg twice daily for 2 weeks (for penicillin-allergic patients) 1
• Syphilis (>1 year duration): 100 mg twice daily for 4 weeks 1
• STI prevention (doxy PEP): 200 mg as a single dose within 72 hours of sexual exposure 2

Other Infections:

• Malaria prophylaxis: 100 mg daily 1
• Inhalational anthrax (post-exposure): 100 mg twice daily for 60 days 1
• Lyme disease: 100 mg twice daily for 10-21 days 3
• Tularemia (mild cases): 100 mg twice daily 2
• Bubonic plague: 100 mg twice daily 2
• Bacillary angiomatosis: 100 mg twice daily for 2 weeks to 2 months 2

Administration Guidelines

• Take with adequate fluid (full glass of water) to reduce risk of esophageal irritation 3
• Remain upright for at least 30 minutes after taking to prevent esophageal irritation 3
• Can be taken with food or milk if gastric irritation occurs 3
• Avoid taking within 2 hours of antacids, iron, calcium, magnesium supplements, or dairy products as these can reduce absorption 3

Important Considerations

Potential Side Effects:

• Common: nausea, vomiting, diarrhea, esophageal irritation, photosensitivity, vaginal yeast infections 3
• Serious: severe skin reactions, difficulty swallowing, severe headache, vision changes, allergic reactions 3

Special Populations:

• Renal impairment: No dosage adjustment needed as doxycycline does not accumulate in patients with renal insufficiency 4
• Pregnancy: Contraindicated (pregnancy category D) 3
• Breastfeeding: Use with caution; azithromycin preferred if available 3

Clinical Pearls

• The therapeutic antibacterial serum activity typically persists for 24 hours following recommended dosage 1
• For streptococcal infections, therapy should continue for at least 10 days 1
• Doxycycline has excellent tissue penetration and achieves therapeutic levels in most organs and tissues 4
• Unlike other tetracyclines, doxycycline's prolonged half-life allows for once-daily administration in many cases 4
• Oral absorption is rapid and nearly complete, with serum concentrations comparable between oral and IV administration 4

Remember that while these are standard recommendations, clinical judgment should be exercised based on infection severity, patient factors, and local antimicrobial resistance patterns.