What is the recommended dose of Doxycycline (DOXY) for bacterial infections?

Doxycycline Dosing for Bacterial Infections

For most 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 maintenance dosing, with severe infections requiring 100 mg every 12 hours throughout treatment. 1

Standard Adult Dosing Algorithm

Loading and Maintenance Approach

• Day 1: Administer 200 mg total (100 mg every 12 hours) 1
• Day 2 onwards: 100 mg once daily for mild-to-moderate infections 1
• Severe infections: Continue 100 mg every 12 hours (200 mg/day total) throughout the treatment course 1

Duration by Infection Type

• Skin and soft tissue infections: 7-14 days at 100 mg twice daily 2, 3
• Respiratory tract infections: 7-21 days at 100 mg twice daily 2
• Sexually transmitted infections (chlamydia, NGU): 100 mg twice daily for 7 days 1
• Early syphilis: 100 mg twice daily for 2 weeks 1
• Late syphilis (>1 year duration): 100 mg twice daily for 4 weeks 1
• Inhalational anthrax: 100 mg twice daily for 60 days 3, 1

Pediatric Dosing (Children >8 Years)

Weight-Based Calculation

• Children ≤45 kg: 2.2 mg/kg every 12 hours 3
• Children >45 kg: Use adult dosing (100 mg twice daily) 3

Loading Dose for Children

• Day 1: 2 mg/lb (4.4 mg/kg/day) divided into two doses 1
• Subsequent days: 1 mg/lb (2.2 mg/kg/day) as single daily dose or divided 1
• Severe infections: May use up to 2 mg/lb (4.4 mg/kg/day) throughout treatment 1

Critical contraindication: Doxycycline is not recommended for children under 8 years due to dental staining and bone growth effects, except when benefits outweigh risks in life-threatening infections 2, 3

Special Dosing Situations

Post-Exposure Prophylaxis for STIs

• Single dose: 200 mg within 72 hours after sexual exposure (maximum 200 mg per 24 hours) 4, 3
• This applies specifically to MSM and transgender women with recent bacterial STI history 4

Malaria Prophylaxis

• Adults: 100 mg once daily 1
• Children >8 years: 2 mg/kg once daily (up to adult dose) 1
• Begin 1-2 days before travel, continue during exposure and for 4 weeks after leaving malarious area 1

Critical Administration Guidelines

Esophagitis Prevention

• Administer with full glass of liquid 4
• Patient must remain upright for at least 1 hour after taking doxycycline 2, 3, 1
• May give with food or milk if gastric irritation occurs without significantly affecting absorption 1

Drug Interactions

• Separate dosing by at least 2 hours from dairy products, antacids, and supplements containing calcium, iron, magnesium, or sodium bicarbonate 3

Photosensitivity Precautions

• Advise patients to avoid direct sunlight and use sun protection, as photosensitivity reactions can be severe 2

Common Pitfalls to Avoid

Dosing Errors

• Do not exceed 200 mg per 24 hours as this increases side effect incidence 1
• The dosing schedule for doxycycline differs from other tetracyclines—exceeding recommendations increases adverse events 1

Duration Mistakes

• For streptococcal infections, continue therapy for 10 days regardless of clinical improvement 1
• Shorter treatment courses (30 days vs 45 days) for brucellosis show higher relapse rates (22.9% vs 5.9%) 5

Renal Impairment

• Usual doses do not lead to excessive accumulation in renal impairment patients—no dose adjustment typically needed 1

Pregnancy and Special Populations

• Generally contraindicated in pregnancy due to effects on developing teeth and bones 3
• May be used for life-threatening infections when benefits outweigh risks 3
• The Infectious Diseases Society of America supports standard dosing for most bacterial infections at 100 mg twice daily for 7-14 days based on clinical response 2, 3