Doxycycline Dosing for Bacterial Infections
For most bacterial infections in adults, doxycycline should be dosed at 100 mg twice daily, with a loading dose of 200 mg on the first day, and 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 (given as 100 mg every 12 hours), followed by 100 mg daily maintenance dosing 1
- For severe infections: Continue 100 mg every 12 hours (twice daily) throughout the treatment course rather than stepping down to once daily 1
- Duration: 7-14 days for most skin and soft tissue infections, including MRSA 2, 3, 4
The FDA label explicitly states that exceeding recommended dosages may increase side effects, so adherence to these parameters is critical 1.
Pediatric Dosing (Children >8 Years)
- Children ≤45 kg (100 lbs): 2.2 mg/kg twice daily (maximum 100 mg per dose) 5, 4, 1
- Children >45 kg: Use adult dosing of 100 mg twice daily 4
- Absolute contraindication: Do not use in children <8 years due to permanent dental staining and enamel hypoplasia, except in life-threatening infections where benefits outweigh risks 2, 4
Condition-Specific Durations
Tickborne Rickettsial Diseases
- Rocky Mountain Spotted Fever/Ehrlichiosis: Minimum 3 days after fever subsides with evidence of clinical improvement; typical minimum course is 5-7 days 5
- Anaplasmosis: Extend to 10 days if concurrent Lyme disease suspected 5
Sexually Transmitted Infections
- Chlamydia (uncomplicated urethral/endocervical/rectal): 100 mg twice daily for 7 days 1, 6
- Nongonococcal urethritis: 100 mg twice daily for 7 days 1
- Acute epididymo-orchitis (chlamydial or gonococcal): 100 mg twice daily for at least 10 days 1
Lyme Disease
- Early localized/disseminated: 100 mg twice daily for 10-21 days (10 days is sufficient per IDSA guidelines) 5, 2
- Post-exposure prophylaxis: Single 200 mg dose within 72 hours of high-risk tick bite 2
Brucellosis
- Uncomplicated: 100 mg twice daily for 6 weeks, preferably combined with streptomycin (2-3 weeks) or gentamicin (7 days) 5
- Monotherapy with doxycycline alone for 6 weeks showed acceptable relapse rates in well-designed trials, though combination therapy remains preferred 5
Other Serious Infections
- Inhalational anthrax (post-exposure): 100 mg twice daily for 60 days 4, 1
- Q fever (acute): 100 mg twice daily for 14 days 2
- Q fever (chronic): 100 mg twice daily plus hydroxychloroquine for ≥18 months 2
- Syphilis (early, penicillin-allergic): 100 mg twice daily for 2 weeks 1
- Syphilis (>1 year duration): 100 mg twice daily for 4 weeks 1
Critical Administration Guidelines
- Take with adequate fluids to reduce esophageal irritation and ulceration risk 1
- Avoid lying down for 1 hour after administration to prevent esophagitis 4
- May be taken with food or milk if gastric irritation occurs; absorption is not significantly affected 1
- Separate from dairy, antacids, calcium, iron, magnesium by at least 2 hours 4
- Complete full course even if symptoms improve early to prevent treatment failure 3
Special Populations
Pregnancy
- Generally contraindicated due to effects on developing teeth and bones 2, 4
- May be used for life-threatening infections (e.g., tickborne rickettsial diseases) when benefits clearly outweigh risks 5, 4
Renal Impairment
- No dosage adjustment required at usual recommended doses 1
- Doxycycline does not accumulate excessively in renal impairment patients 1
Common Pitfalls to Avoid
- Inadequate duration: Treatment courses <7 days for bacterial infections lead to treatment failure 3
- Premature discontinuation: For rickettsial diseases, stopping before 3 days after fever resolution increases relapse risk 5
- Single daily dosing for severe infections: The FDA label specifies twice-daily dosing for severe infections, not once-daily maintenance dosing 1
- Using in young children: The dental staining risk in children <8 years is permanent; reserve for truly life-threatening situations only 2, 4