Doxycycline Dosing for Pediatric Patients
For children ≥8 years old and weighing <100 pounds, doxycycline should be dosed at 2 mg/lb (approximately 4.4 mg/kg) divided into two doses on day 1, followed by 1 mg/lb (approximately 2.2 mg/kg) daily as a single dose or divided into two doses on subsequent days; for children ≥8 years old weighing ≥100 pounds, use adult dosing of 200 mg on day 1 (100 mg every 12 hours) followed by 100 mg daily. 1
Age-Based Restrictions and Safety Considerations
Doxycycline should generally not be used in children <8 years of age unless the benefits clearly outweigh the risks, primarily due to concerns about permanent tooth discoloration and enamel hypoplasia. 1
However, recent evidence suggests that doxycycline at standard doses (10 mg/kg/day for 2-3 days, then 5 mg/kg/day) does not appear to cause permanent tooth staining in young children, unlike older tetracyclines. 2
For severe infections where doxycycline is necessary in children <8 years old (such as certain tick-borne diseases or life-threatening infections), the dosing is 2-4 mg/kg/day divided into 2 doses (maximum 200-400 mg/day). 1
Weight-Based Dosing Algorithm
For Children ≥8 Years Old:
<100 pounds (45 kg):
- Day 1: 2 mg/lb divided into 2 doses (approximately 4.4 mg/kg/day)
- Subsequent days: 1 mg/lb as single daily dose or divided into 2 doses (approximately 2.2 mg/kg/day) 1
≥100 pounds (45 kg):
- Day 1: 200 mg (100 mg every 12 hours)
- Subsequent days: 100 mg daily 1
For Children <8 Years Old (When Absolutely Necessary):
Standard dosing for severe infections: 2-4 mg/kg/day divided into 2 doses, with a maximum daily dose not exceeding adult dosing 1
For specific conditions like Bartonella endocarditis: 2-4 mg/kg/day IV/PO in 2 divided doses 1
Indication-Specific Considerations
For acne vulgaris (the FDA-approved pediatric indication), doxycycline should be used as adjunctive therapy, not as monotherapy. 1
For atypical pneumonia (Mycoplasma or Chlamydophila) in children >7 years old, doxycycline is dosed at 2-4 mg/kg/day in 2 divided doses. 1
For Lyme disease in children ≥8 years old, standard weight-based dosing applies, though specific duration depends on disease manifestation. 1
Important Clinical Caveats
Maximum daily dose should never exceed adult dosing, regardless of the child's weight. 1
Pharmacokinetic studies demonstrate that allometrically scaled clearance and volume of distribution do not differ significantly between children 2-8 years and those >8 years, supporting consistent per-kilogram dosing across pediatric age groups when the drug is indicated. 3
Avoid doxycycline monotherapy for bacterial infections; it should be used as part of combination therapy or for specific susceptible organisms. 1
Drug interactions are significant: avoid concurrent use with antacids containing aluminum, calcium, or magnesium; iron preparations; bismuth subsalicylate; and be cautious with hormonal contraceptives in adolescents. 1
Gastrointestinal side effects (nausea, vomiting, esophagitis) are common; advise taking with adequate fluids and avoiding lying down immediately after administration. 1
Photosensitivity is a significant concern; counsel patients and families about sun protection during treatment. 1
Doxycycline is Pregnancy Category D and is distributed into breast milk, requiring careful risk-benefit assessment in adolescent females. 1