What is the dosage and treatment regimen for doxycycline?

Doxycycline Dosage and Treatment Regimen

The standard dosage for doxycycline in adults is 100 mg twice daily (200 mg on the first day), with specific durations based on the infection being treated. 1

Standard Adult Dosing

• Initial dose: 200 mg on first day (100 mg every 12 hours)
• Maintenance dose: 100 mg daily or 100 mg every 12 hours for more severe infections 1
• Administration: Take with adequate fluid to reduce esophageal irritation; remain upright for at least 30 minutes after taking 2
• Food interactions: Can be taken with food or milk if gastric irritation occurs; avoid taking within 2 hours of antacids, iron, calcium, magnesium supplements, or dairy products 2

Pediatric Dosing (Children >8 years)

• Weight ≤100 lbs: 2 mg/lb divided into two doses on day 1, then 1 mg/lb daily (single dose or divided) on subsequent days
• Weight >100 lbs: Use adult dosing 1
• Important: Doxycycline should be avoided in children under 8 years due to risk of dental staining and enamel hypoplasia 2

Specific Treatment Regimens by Infection

Sexually Transmitted Infections

• Chlamydia: 100 mg twice daily for 7 days 2, 1
• Nongonococcal urethritis: 100 mg twice daily for 7 days 2, 1
• Uncomplicated gonococcal infections: 100 mg twice daily for 7 days (alternative: 300 mg stat followed by 300 mg one hour later) 1
• STI prevention (Doxy PEP): 200 mg as single dose within 72 hours of sexual exposure 2

Tick-Borne Diseases

• Lyme disease prophylaxis: 200 mg single dose 2
• Lyme disease treatment: 100 mg twice daily for 10-21 days 2
  • Note: Research shows no benefit to extending treatment from 10 to 20 days for erythema migrans 3
• Human Granulocytic Anaplasmosis: 100 mg twice daily for 10 days 2

Skin and Soft Tissue Infections

• Outpatient MRSA skin infections: 100 mg twice daily for 5-10 days 2

Other Infections

• Malaria prophylaxis: 100 mg daily (adults); 2 mg/kg daily (children >8 years) 1
• Inhalational anthrax (post-exposure): 100 mg twice daily for 60 days 1
• Syphilis (early) in penicillin-allergic patients: 100 mg twice daily for 2 weeks 1
• Syphilis (>1 year duration) in penicillin-allergic patients: 100 mg twice daily for 4 weeks 1
• Acute epididymo-orchitis: 100 mg twice daily for at least 10 days 1
• Respiratory tract infections: 200 mg on first day, then 100 mg daily (can continue 200 mg daily in severe cases) 4

Important Clinical Considerations

Efficacy

• Doxycycline shows high efficacy rates:
  • 98.8% clearance for asymptomatic rectal chlamydia with 7-day regimen 5
  • 87% good/very good results for respiratory infections 4
  • Promising results for multidrug-resistant gram-negative bacterial infections 6

Contraindications and Precautions

• Pregnancy: Contraindicated (pregnancy category D); may be used for short periods (7-14 days) before 6 months gestation for life-threatening infections when alternatives aren't available 2
• Breastfeeding: Azithromycin preferred, but doxycycline can be used with close monitoring of infant 2
• Children <8 years: Avoid due to dental staining risk 2

Common Side Effects

• Nausea, vomiting, diarrhea
• Esophageal irritation
• Photosensitivity
• Vaginal yeast infections 2

Administration Pearls

• Take with full glass of water
• Remain upright for 30 minutes after taking
• Use sunscreen and protective clothing due to photosensitivity
• Can take with food if gastric irritation occurs
• Avoid antacids, iron, calcium, magnesium, and dairy products within 2 hours of dosing 2

Treatment Duration Considerations

• Most bacterial infections: 7-10 days
• Specific durations vary by infection type as noted above
• For STIs: Abstain from sexual intercourse until 7 days after therapy initiation and symptoms resolve 2
• Monitor for antimicrobial resistance with prolonged use 2