Doxycycline Dosage and Treatment Duration for Bacterial Infections
The standard dosage of doxycycline for most bacterial infections in adults is 100 mg twice daily, with a loading dose of 200 mg on the first day, followed by maintenance doses for durations specific to each infection type. 1
Standard Dosing Regimens
Adults:
- Initial dose: 200 mg on first day (100 mg every 12 hours)
- Maintenance dose: 100 mg daily or 100 mg every 12 hours for more severe infections
Children (>8 years):
- Initial dose: 2 mg/lb (4.4 mg/kg) divided into two doses on first day
- Maintenance dose: 1 mg/lb (2.2 mg/kg) daily or divided into two doses
- Note: Not recommended for children under 8 years of age 2
Infection-Specific Treatment Regimens
Skin and Soft Tissue Infections
- MRSA/MSSA skin infections: 100 mg twice daily for 7-14 days 2
- Impetigo: Not first-line therapy
Sexually Transmitted Infections
- Uncomplicated chlamydial infections: 100 mg twice daily for 7 days 3
- Nongonococcal urethritis: 100 mg twice daily for 7 days 1
- Uncomplicated gonococcal infections: 100 mg twice daily for 7 days (alternative: 300 mg stat followed by 300 mg one hour later) 1
- Epididymo-orchitis: 100 mg twice daily for at least 10 days 1
Syphilis
- Early syphilis (penicillin-allergic patients): 100 mg twice daily for 2 weeks 1
- Late syphilis (>1 year duration): 100 mg twice daily for 4 weeks 1
Respiratory Tract Infections
- Acute bronchitis/exacerbations of chronic bronchitis: 100 mg twice daily for 5-7 days 4
Tick-Borne Diseases
- Tularemia (mild cases): 100 mg twice daily for 14 days 2
- Bubonic plague: 100 mg twice daily for 10-14 days 2
Bioterrorism-Related Infections
- Inhalational anthrax post-exposure: 100 mg twice daily for 60 days 2, 1
- Cutaneous anthrax: 100 mg twice daily for 60 days (due to risk of simultaneous aerosol exposure) 2
Other Infections
- Bacillary angiomatosis: 100 mg twice daily for 4 weeks 2
- Cat-scratch disease: Alternative to azithromycin 2
Special Considerations
Administration Guidelines
- Take with adequate fluid to reduce risk of esophageal irritation
- Can be taken with food or milk if gastric irritation occurs
- Absorption not markedly influenced by simultaneous food or milk ingestion 1
Contraindications and Cautions
- Avoid in children under 8 years due to dental staining and enamel hypoplasia
- Avoid in pregnancy due to fetal risks
- No dosage adjustment needed in renal impairment 1
Antimicrobial Resistance Considerations
- Long-term sub-antimicrobial dosing (20 mg twice daily) has not shown to induce resistance in intestinal flora 5
- Doxycycline has shown promising results against multidrug-resistant gram-negative bacterial infections 6
Treatment Monitoring
- Clinical response typically occurs within 3-5 days for respiratory infections 4
- For streptococcal infections, continue therapy for 10 days to prevent rheumatic fever 1
- Test of cure recommended 14-28 days post-treatment for certain infections like Mycoplasma genitalium 7
Common Pitfalls to Avoid
- Inadequate loading dose on first day
- Premature discontinuation before completing full course
- Failure to adjust dosing in severe infections
- Concurrent administration with antacids, calcium, iron, or magnesium supplements (take doxycycline 2 hours before or after)
- Using doxycycline as monotherapy for severe systemic infections where combination therapy is indicated
When selecting doxycycline for bacterial infections, consider the pathogen, infection site, severity, and patient factors to determine appropriate dosing and duration.