What is the typical treatment regimen for an adult or adolescent patient with a diagnosed infection using doxycycline (antibiotic)?

Doxycycline Treatment for Infection

Standard Adult Dosing Regimen

For most bacterial infections in adults, doxycycline should be administered as 200 mg on the first day (given as 100 mg every 12 hours), followed by a maintenance dose of 100 mg daily; for more severe infections, particularly chronic urinary tract infections, continue 100 mg every 12 hours throughout the treatment course. 1

Infection-Specific Dosing

Sexually Transmitted Infections:

• Chlamydia trachomatis (urethral, endocervical, or rectal): 100 mg orally twice daily for 7 days 2, 1
• Nongonococcal urethritis (NGU): 100 mg orally twice daily for 7 days 1
• Gonorrhea (uncomplicated, except anorectal in men): 100 mg orally twice daily for 7 days, PLUS treatment must include coverage for presumptive chlamydial coinfection 2
• Early syphilis (penicillin-allergic patients): 100 mg orally twice daily for 2 weeks 1
• Late syphilis (>1 year duration, penicillin-allergic): 100 mg orally twice daily for 4 weeks 1
• Acute epididymo-orchitis (gonococcal or chlamydial): 100 mg orally twice daily for at least 10 days 1

Skin and Soft Tissue Infections:

• Outpatient MRSA or other skin infections: 100 mg orally twice daily for 7-14 days 3, 4
• For mild to moderate infections: 100 mg twice daily is sufficient 3
• For severe infections: Treatment duration may extend to 14 days but generally should not exceed this 3

Other Infections:

• Bartonellosis (bacillary angiomatosis, peliosis hepatis): Doxycycline with or without rifampin for >3 months; for CNS involvement, doxycycline plus rifampin is preferred 2
• Mycoplasma infections: 100 mg orally twice daily for 7 days 5
• Respiratory tract infections: 200 mg on day 1, then 100 mg daily (or 200 mg daily for severe cases) 6

Prophylactic Indications:

• Malaria prophylaxis: 100 mg daily, starting 1-2 days before travel and continuing for 4 weeks after leaving malarious area 1
• Inhalational anthrax (post-exposure): 100 mg orally twice daily for 60 days 1

Pediatric Dosing

Children ≥8 years old weighing ≤100 lbs (45 kg):

• Initial dose: 2 mg/lb (4.4 mg/kg) divided into two doses on day 1 1
• Maintenance: 1 mg/lb (2.2 mg/kg) daily as single dose or divided into two doses 1
• Severe infections: Up to 2 mg/lb (4.4 mg/kg) daily may be used 1

Children ≥8 years old weighing >100 lbs (45 kg):

• Use standard adult dosing 1

Critical contraindication: Doxycycline should NOT be used in children <8 years of age due to risk of permanent tooth discoloration and enamel hypoplasia 3, 5

Administration Guidelines and Clinical Pearls

Administration:

• Administer with adequate fluid (at least 8 oz of water) and patient should remain upright for at least 1 hour after taking to prevent esophageal irritation and ulceration 5, 1
• If gastric irritation occurs, may be given with food or milk without significantly affecting absorption 1
• Avoid taking with antacids, calcium, magnesium, or iron-containing preparations as these reduce absorption 4

Duration Considerations:

• Complete the full course even if symptoms improve before completion 3
• Inadequate duration (<7 days) may lead to treatment failure 3
• For streptococcal infections, continue therapy for 10 days 1
• Clinical improvement should be evident within 48-72 hours of initiating therapy 5

Special Populations

Renal Impairment:

• No dosage adjustment typically required; doxycycline does not accumulate excessively in patients with renal impairment 1

Hepatic Impairment:

• Use with caution; severe liver dysfunction is a contraindication 7

Pregnancy and Breastfeeding:

• Contraindicated (Pregnancy Category D) due to risk of hepatotoxicity and effects on fetal bone and tooth development 4, 5
• Generally contraindicated in breastfeeding; consider alternative antibiotics 3

Common Adverse Effects and Precautions

Frequent Side Effects:

• Gastrointestinal symptoms (nausea, vomiting, diarrhea) are common 5, 7
• Photosensitivity reactions can be severe; patients must avoid direct sunlight and use sun protection 5
• Esophagitis and esophageal ulceration, particularly with inadequate fluid intake 5, 1

Serious Adverse Effects:

• Pill-associated ulcerative esophagitis (most common when taken with minimal liquid or at bedtime) 2
• Phototoxic reactions 7

Antimicrobial Resistance Considerations

Emerging Resistance Concerns:

• Doxycycline PEP for STI prevention accelerates tetracycline resistance in N. gonorrhoeae, with clinical effectiveness potentially lost within 1.6-12.1 years depending on uptake levels 8
• Despite resistance concerns, doxycycline remains effective for most indicated infections with bacterial resistance having low incidence in many regions 7
• Therapeutic success rates of approximately 80% can be expected in respiratory and urinary tract infections 7

Alternative Formulations

Delayed-Release Doxycycline (Doryx):

• 200 mg orally once daily for 7 days is non-inferior to standard twice-daily dosing for uncomplicated urogenital chlamydia 2
• May improve adherence and is better tolerated with less nausea and vomiting (13% vs 21% and 8% vs 12%, respectively) 2

Clinical Effectiveness

Doxycycline demonstrates excellent tissue penetration with therapeutic levels achieved in kidney, lung, gallbladder, prostate, intestinal tract, myocardium, sinus secretions, tonsil, aqueous humor, and female reproductive tissue 9. The prolonged half-life allows once-daily administration for certain indications 9. Therapeutic antibacterial serum activity typically persists for 24 hours following recommended dosage 1.