What is the dosage and treatment duration for doxycycline (Doxycycline) in bacterial infections?

Doxycycline Dosing and Duration for Bacterial Infections

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 ranging from 5-14 days depending on the specific infection. 1

Standard Adult Dosing Regimen

• Loading dose: 200 mg on day 1, administered as 100 mg every 12 hours 1
• Maintenance dose: 100 mg twice daily for the duration of treatment 1
• For severe infections (particularly chronic urinary tract infections), continue 100 mg every 12 hours throughout the treatment course 1

Pediatric Dosing (Children >8 Years)

• Children ≤100 lbs: 2 mg/lb body weight divided into two doses on day 1, then 1 mg/lb daily (as single dose or divided) 1
• For severe infections: up to 2 mg/lb body weight may be used 1
• Children >100 lbs: use standard adult dosing 1
• Critical caveat: Doxycycline is contraindicated in children <8 years due to permanent tooth discoloration and enamel hypoplasia, except when benefits outweigh risks in life-threatening infections 2, 3

Infection-Specific Duration Guidelines

Skin and Soft Tissue Infections

• Duration: 7 days for uncomplicated cases 3
• Dosing: 100 mg twice daily orally for both MSSA and MRSA infections 3, 2
• Treatment duration may extend to 14 days for severe infections 2

Tickborne Rickettsial Diseases (RMSF, Ehrlichiosis, Anaplasmosis)

• Duration: Minimum 5-7 days, continuing at least 3 days after fever subsides and until clinical improvement is evident 3, 4
• Dosing: Adults receive 100 mg twice daily; children <100 lbs receive 2.2 mg/kg twice daily 3
• For anaplasmosis with suspected Lyme coinfection, extend treatment to 10 days 3

Sexually Transmitted Infections

Chlamydia and NGU: 100 mg twice daily for 7 days 1

Uncomplicated gonorrhea: 100 mg twice daily for 7 days (alternative regimen: 300 mg stat, then 300 mg one hour later) 1

Syphilis (penicillin-allergic patients):

• Early syphilis: 100 mg twice daily for 2 weeks 1
• Late syphilis (>1 year duration): 100 mg twice daily for 4 weeks 1

Doxycycline PEP for STI prevention: Single 200 mg dose within 72 hours after sexual exposure, not exceeding 200 mg per 24 hours 3, 5

Anthrax (Bioterrorism/Post-Exposure)

• Inhalational anthrax: 100 mg twice daily for 60 days (adults); 2.2 mg/kg twice daily for 60 days (children <100 lbs) 3, 1
• Cutaneous anthrax: 100 mg twice daily for 7-10 days for community-acquired cases, but extend to 60 days if aerosol exposure is suspected 3

Brucellosis

• Duration: 6 weeks 3
• Dosing: 100 mg twice daily orally, preferably combined with streptomycin (15 mg/kg daily IM for 2-3 weeks) or gentamicin (5 mg/kg daily for 7 days) 3
• Monotherapy with doxycycline alone is associated with higher relapse rates and should be avoided 3

Respiratory Tract Infections

• Duration: 5-10 days, with most patients showing improvement by days 3-5 6, 7
• Dosing: 200 mg on day 1, then 100 mg daily 6, 7
• Clinical success rates of approximately 80% for community-acquired respiratory infections 8

Critical Administration Guidelines

• Administer with adequate fluids to reduce risk of esophageal irritation and ulceration 1
• May be given with food or milk if gastric irritation occurs; absorption is not significantly affected 1
• Avoid sun exposure due to photosensitivity risk 5, 8
• No renal dose adjustment required in patients with renal impairment 1

Common Pitfalls to Avoid

1. Inadequate treatment duration: Stopping therapy before 5-7 days or before clinical improvement increases treatment failure risk 2
2. Streptococcal infections require 10 days: When treating streptococcal infections, always continue therapy for the full 10-day course 1
3. Exceeding recommended dosage: This increases side effect incidence without improving efficacy 1
4. Using in pregnancy: Doxycycline is generally contraindicated during pregnancy; alternative agents should be used 5
5. Delaying treatment in rickettsial diseases: Treatment should never be delayed while awaiting laboratory confirmation, as delay leads to severe disease and mortality 3