What is the typical dosage and treatment duration of Doxycycline for bacterial infections?

Doxycycline Dosing and Duration for Bacterial Infections

For most common bacterial infections in adults, doxycycline should be dosed at 200 mg on day 1 (given as 100 mg every 12 hours), followed by 100 mg daily or 100 mg twice daily for severe infections, with treatment duration typically 7-14 days depending on clinical response. 1

Standard Adult Dosing

The FDA-approved regimen begins with a loading dose of 200 mg on the first day (administered as 100 mg every 12 hours), then transitions to 100 mg daily for maintenance therapy. 1

• For severe infections, particularly chronic urinary tract infections, 100 mg every 12 hours should be continued throughout the treatment course 1
• Most skin and soft tissue infections require 100 mg twice daily for 7-14 days based on clinical improvement 2
• The therapeutic serum activity persists for 24 hours after dosing, supporting once-daily maintenance regimens for less severe infections 1

Infection-Specific Durations

Short-Course Therapy (7-10 Days)

• Cutaneous anthrax: 7-10 days (though 60 days if aerosol exposure suspected) 3
• Chlamydial infections (urethral, endocervical, rectal): 7 days at 100 mg twice daily 1
• Non-gonococcal urethritis: 7 days at 100 mg twice daily 1
• Uncomplicated gonococcal infections: 7 days at 100 mg twice daily 1

Intermediate-Duration Therapy (10-14 Days)

• Acute epididymo-orchitis: minimum 10 days at 100 mg twice daily 1
• Streptococcal infections: 10 days 1
• MRSA skin infections: 7-14 days at 100 mg twice daily 2

Extended-Duration Therapy

• Early syphilis: 2 weeks at 100 mg twice daily (penicillin-allergic patients) 1
• Late syphilis (>1 year duration): 4 weeks at 100 mg twice daily 1
• Inhalational anthrax: 60 days at 100 mg twice daily (IV initially, then oral) 3, 1

Pediatric Dosing

Children >100 pounds (>45 kg)

Use adult dosing: 200 mg day 1 (100 mg every 12 hours), then 100 mg daily maintenance 1

Children ≤100 pounds (≤45 kg) and >8 years old

• Day 1: 2 mg/lb divided into two doses 1
• Subsequent days: 1 mg/lb as single daily dose or divided into two doses 1
• For severe infections: up to 2 mg/lb may be used 1

Children ≤8 years old

Doxycycline is generally contraindicated due to dental staining risk, except for life-threatening infections (anthrax, Rocky Mountain spotted fever, plague) where benefits outweigh risks 2, 4

• Dosing when indicated: 2.2 mg/kg every 12 hours 3, 4

Critical Administration Guidelines

Esophageal Protection

Administer with adequate fluid and avoid lying down for 1 hour after dosing to prevent esophagitis and esophageal ulceration 1, 3

Food Interactions

• May be given with food or milk if gastric irritation occurs without significantly affecting absorption 1
• Avoid concurrent administration with dairy products, antacids, or supplements containing calcium, iron, magnesium, or sodium bicarbonate (separate by at least 2 hours) 2

Photosensitivity

Counsel patients about photosensitivity risk and recommend sun protection measures 3

Special Populations

Pregnancy

Doxycycline may be used for life-threatening infections when benefits outweigh risks (e.g., inhalational anthrax where mortality risk is extremely high) 3, 2

Renal Impairment

Dose adjustment is not required as doxycycline does not accumulate excessively in renal impairment 1

Hepatic Impairment

Contraindicated in severe liver dysfunction 5

Common Pitfalls to Avoid

• Do not exceed 200 mg per 24-hour period to minimize side effects 1, 3
• Do not use cephalosporins or trimethoprim-sulfamethoxazole for anthrax as they are ineffective 3
• Do not use doxycycline as monotherapy for inhalational anthrax initially; combine with a second agent due to high mortality 3
• Do not discontinue streptococcal infection treatment before 10 days to prevent rheumatic fever complications 1
• Do not routinely prescribe to children <8 years unless treating life-threatening infections where no alternative exists 2, 4