What is the treatment for a tick bite with a bull's eye rash, also known as erythema migrans (EM), indicative of Lyme disease?

Treatment for Tick Bite with Bull's Eye Rash (Erythema Migrans)

Start oral doxycycline 100 mg twice daily for 10 days immediately—this is the preferred first-line treatment for erythema migrans in adults and children ≥8 years old. 1

Diagnosis

The bull's eye rash (erythema migrans) is pathognomonic for Lyme disease and should be diagnosed clinically without waiting for laboratory testing. 1 Key diagnostic features include:

• Do not order serological testing for typical erythema migrans—clinical diagnosis is strongly recommended over laboratory testing in endemic areas 1
• The rash typically appears 7-14 days (range 3-30 days) after tick detachment and is usually ≥5 cm in diameter 2
• The lesion may appear homogeneously erythematous or have central clearing with a target-like appearance 2

First-Line Treatment Regimen

Doxycycline is the preferred antibiotic with strong evidence supporting its efficacy: 1

• Adults: 100 mg orally twice daily for 10 days 1, 2, 3
• Children ≥8 years: 4 mg/kg per day in 2 divided doses (maximum 100 mg per dose) for 10 days 2

The 10-day course with doxycycline is supported by multiple trials showing equivalent efficacy to longer courses, with approximately 90% clearance of signs and symptoms and <5% relapse rate at 6 months. 4, 5

Alternative Treatment Options

When doxycycline cannot be used (pregnancy, breastfeeding, children <8 years, or contraindications):

Amoxicillin: 1

• Adults: 500 mg orally three times daily for 14 days
• Children: 50 mg/kg/day in 3 divided doses (maximum 500 mg per dose) for 14 days 2

Cefuroxime axetil: 1

• Adults: 500 mg orally twice daily for 14 days
• Children: 30 mg/kg/day in 2 divided doses (maximum 500 mg per dose) for 14 days 2

Azithromycin (second-line only): 1

• Use only if patient cannot take both doxycycline and beta-lactam antibiotics
• 5-10 days, with 7-day course preferred in the United States 1
• Note: Macrolides have lower efficacy than doxycycline or beta-lactams 5

Special Population Considerations

Pregnant women: 6

• Avoid doxycycline due to risk of permanent tooth discoloration and bone formation issues in the fetus
• Use amoxicillin as first-line alternative 6
• Favorable outcomes expected with standard antibiotic regimens—no evidence of congenital Lyme disease syndrome 1

Expected Clinical Response and Monitoring

• Fever should subside within 24-48 hours after initiating doxycycline 2
• Lack of clinical response within 48 hours may indicate alternative diagnosis or coinfection 2
• Monitor all patients for clinical improvement over the treatment course 2
• Educate patients about possible Jarisch-Herxheimer reaction (temporary worsening of symptoms after starting antibiotics) 2

Critical Pitfalls to Avoid

Do not delay treatment waiting for laboratory confirmation in patients with typical erythema migrans in endemic areas—this increases risk of progression to neurologic, cardiac, or rheumatologic complications. 1, 2

Do not extend treatment beyond recommended durations without evidence of disseminated disease—there is no convincing evidence that longer therapy improves outcomes for early Lyme disease. 7, 4

Geographic consideration: In southern United States where lone star tick (Amblyomma americanum) causes Southern Tick-Associated Rash Illness (STARI), distinguishing from Lyme disease may be impossible clinically. When STARI cannot be distinguished from Lyme disease in areas endemic for both conditions, treat for Lyme disease. 1, 3

When to Hospitalize

Hospitalize patients with: 2

• Evidence of organ dysfunction
• Severe thrombocytopenia
• Mental status changes
• Need for supportive therapy