What is the recommended dose of doxycycline (antibiotic) for treating common bacterial infections in adults?

Doxycycline Dosing for Common Bacterial Infections in Adults

For most common bacterial infections in adults, doxycycline should be dosed at 200 mg on the first day (given as 100 mg every 12 hours), followed by 100 mg daily as maintenance therapy. 1

Standard Dosing Regimen

The FDA-approved dosing follows a loading dose approach:

• Day 1 (Loading): 200 mg total (administered as 100 mg every 12 hours) 1
• Maintenance (Day 2 onward): 100 mg once daily 1
• Severe infections: 100 mg every 12 hours may be continued throughout treatment 1

Infection-Specific Dosing

Respiratory Tract Infections

• Acute bronchitis/exacerbations of chronic bronchitis: 200 mg on day 1, then 100 mg daily 2
• Community-acquired pneumonia: 100 mg IV every 12 hours for hospitalized patients 3
• Clinical response typically occurs within 2-3 days, with most patients improving by days 3-5 2

Sexually Transmitted Infections

• Uncomplicated urethral, endocervical, or rectal chlamydia: 100 mg twice daily for 7 days 1
• Nongonococcal urethritis (NGU): 100 mg twice daily for 7 days 1
• Uncomplicated gonorrhea: 100 mg twice daily for 7 days 1
• Early syphilis (penicillin allergy): 100 mg twice daily for 2 weeks 1
• Late syphilis (>1 year duration): 100 mg twice daily for 4 weeks 1

Tick-Borne Infections

• Human Granulocytic Anaplasmosis (HGA): 100 mg twice daily (oral or IV) for 10 days 4
• Treatment should not be delayed pending laboratory confirmation if clinical suspicion is high 4
• Clinical improvement expected within 24-48 hours; lack of response warrants reevaluation 4

Other Infections

• Acute epididymo-orchitis: 100 mg twice daily for at least 10 days 1
• Inhalational anthrax (post-exposure): 100 mg twice daily for 60 days 1
• Malaria prophylaxis: 100 mg once daily, starting 1-2 days before travel and continuing 4 weeks after leaving endemic area 1

Administration Considerations

Critical administration points to prevent complications:

• Administer with adequate fluid (full glass of water) to reduce esophageal irritation and ulceration risk 1
• May be given with food or milk if gastric irritation occurs, as absorption is not significantly affected 1
• Therapeutic serum activity persists for 24 hours after recommended dosing 1

Severe Infections

For chronic urinary tract infections and other severe infections, maintain 100 mg every 12 hours throughout the treatment course rather than stepping down to once-daily dosing. 1

Duration of Therapy

Treatment duration varies by infection type:

• Most respiratory infections: 7-10 days 2
• Streptococcal infections: Minimum 10 days 1
• STIs: 7 days for uncomplicated infections 1
• HGA: 10 days 4

Common Pitfalls to Avoid

• Inadequate hydration during administration increases risk of esophageal ulceration 1
• Premature discontinuation before completing the full course, particularly in streptococcal infections where 10 days is mandatory 1
• Using once-daily dosing for severe infections when twice-daily dosing is more appropriate 1
• Failing to reassess patients who don't respond within 24-48 hours of initiating therapy for tick-borne illnesses 4

Special Populations

Renal impairment: No dose adjustment required; doxycycline does not accumulate excessively in renal impairment at usual recommended doses 1

Pediatric patients >8 years and >100 lbs: Use adult dosing 1

Pediatric patients >8 years and ≤100 lbs: 2 mg/lb divided into two doses on day 1, then 1 mg/lb daily (or divided twice daily for severe infections, up to 2 mg/lb) 1