What are the dosages and durations for each of the three antibiotic regimens used to treat early Lyme disease?

Three Antibiotic Regimens for Early Lyme Disease: Dosages and Durations

The three first-line oral antibiotic regimens for treating early Lyme disease in adults are: doxycycline 100 mg twice daily for 10-21 days (14 days recommended), amoxicillin 500 mg three times daily for 14-21 days, and cefuroxime axetil 500 mg twice daily for 14-21 days. 1

Adult Dosing Regimens

Doxycycline

• Dosage: 100 mg orally twice daily 1
• Duration: 14 days (range 10-21 days) 1
• Key advantage: Ten days of therapy is sufficient with doxycycline due to its longer half-life, though 14 days is recommended for uniformity 1
• Additional benefit: Effective for concurrent human granulocytic anaplasmosis (HGA), which may occur simultaneously with Lyme disease 1

Amoxicillin

• Dosage: 500 mg orally three times daily 1
• Duration: 14-21 days 1
• Important note: The full 14-day course is required due to the shorter half-life of β-lactam antibiotics compared to doxycycline 1

Cefuroxime Axetil

• Dosage: 500 mg orally twice daily 1
• Duration: 14-21 days 1
• Rationale: Like amoxicillin, the 14-day minimum is necessary due to the shorter half-life of β-lactam drugs 1

Pediatric Dosing Regimens

For Children ≥8 Years Old

• Doxycycline: 4 mg/kg per day in 2 divided doses (maximum 100 mg per dose) for 14 days 1, 2

For Children <8 Years Old

• Amoxicillin: 50 mg/kg per day in 3 divided doses (maximum 500 mg per dose) for 14 days 1, 2
• Cefuroxime axetil: 30 mg/kg per day in 2 divided doses (maximum 500 mg per dose) for 14 days 1, 2

Clinical Trial Evidence Supporting These Regimens

The dosing recommendations are based on multiple prospective randomized controlled trials that demonstrated comparable efficacy across all three regimens 1. A landmark trial of 180 patients specifically evaluated duration, comparing 10 days versus 20 days of doxycycline, and found no difference in complete response rates (83.9% vs 90.3% at 30 months, P > 0.2) 3. This supports the adequacy of shorter courses with doxycycline, though guidelines recommend 14 days for consistency 1.

Important Administration Considerations

• Doxycycline: Should be taken with 8 ounces of fluid to reduce esophageal irritation and with food to minimize gastrointestinal intolerance 1, 4
• Sun exposure: Patients on doxycycline must avoid sun exposure due to photosensitivity risk 1, 4
• Contraindications: Doxycycline is relatively contraindicated in pregnant or lactating women and children under 8 years of age 1

Common Pitfalls to Avoid

• First-generation cephalosporins (e.g., cephalexin) are inactive against B. burgdorferi and should never be used 1, 2
• Macrolide antibiotics (azithromycin, clarithromycin, erythromycin) are less effective than the three first-line regimens and should only be reserved for patients intolerant of all first-line options 1
• Extending treatment beyond 21 days is not supported by evidence and does not improve outcomes 1, 3