What is the recommended antibiotic regimen for an otherwise healthy adult with uncomplicated cat‑scratch disease (Bartonella henselae)?

Recommended Antibiotic for Cat Scratch Disease

For an otherwise healthy adult with uncomplicated cat-scratch disease, azithromycin 500 mg on day 1 followed by 250 mg daily for 4 additional days is the first-line treatment. 1

Treatment Algorithm for Immunocompetent Adults

First-Line Therapy

• Azithromycin is recommended as first-line treatment based on placebo-controlled evidence showing more rapid reduction in lymph node size compared to placebo. 1, 2
• Dosing for adults >45 kg: 500 mg orally on day 1, then 250 mg daily for 4 additional days (total 5 days). 1, 3
• This recommendation comes from the American College of Physicians and represents the highest quality evidence available. 1

Alternative Regimens (If Azithromycin Contraindicated)

• Doxycycline 100 mg orally twice daily is the preferred alternative, recommended by the CDC. 1, 4

  • Treatment duration: 10-14 days. 4
  • This is a longer course than azithromycin but provides excellent efficacy. 4

• Erythromycin 500 mg orally four times daily is another CDC-recommended alternative. 1

  • This option is particularly important for pregnant or breastfeeding women, as it is the only safe macrolide in these populations. 1

Antibiotics to Avoid

• Penicillins and first-generation cephalosporins have no in vivo activity against Bartonella and should never be used. 1
• Quinolones and trimethoprim-sulfamethoxazole have variable activity and inconsistent clinical response; they are not recommended. 1

When Treatment Is Actually Necessary

Indications for Antibiotic Therapy

• Most cases of uncomplicated cat-scratch disease in immunocompetent patients are self-limited and resolve within 1-6 months without antibiotics. 1, 5, 6
• Treatment is specifically recommended for:
  • Immunocompromised patients (any degree of immunosuppression). 1
  • Extranodal or disseminated disease (occurs in ≤2% of cases). 1, 3
  • Severe symptoms or complications (hepatosplenic involvement, neuroretinitis, encephalopathy). 1, 5
  • Patients desiring faster symptom resolution. 1, 2

Clinical Pitfall

• Approximately 10% of patients develop suppuration of lymph nodes, but this does not automatically require antibiotics unless other indications are present. 1, 3

Important Clinical Context

Diagnosis Confirmation

• Classic presentation: papule/pustule 3-30 days after cat scratch, followed by regional lymphadenopathy ~3 weeks post-inoculation. 1, 3, 6
• Serologic testing may not show detectable antibodies until 6 weeks after acute infection, so early negative serology does not exclude the diagnosis. 1
• High titers (>1:256) of IgG antibody to B. henselae support the diagnosis. 6

Prevention Counseling

• Promptly wash any cat scratch with soap and water immediately—this is the single most important preventive measure. 1
• Implement comprehensive flea control for cats, as cat fleas (Ctenocephalides felis) are the vector for B. henselae transmission between cats. 1, 7
• Avoid rough play with cats and do not allow cats to lick open wounds. 1

Distinguishing From Acute Wound Infection

• If treating an acute infected cat scratch (not cat-scratch disease), the pathogen is typically Pasteurella multocida, and amoxicillin-clavulanate is first-line, not azithromycin. 4
• Cat-scratch disease (Bartonella henselae) presents with delayed lymphadenopathy weeks after exposure, not acute wound infection. 1, 3