Antibiotic Treatment for Cat Scratch Disease
Azithromycin is the first-line antibiotic for cat scratch disease, dosed at 500 mg on day 1 followed by 250 mg daily for 4 additional days in adults (or 10 mg/kg then 5 mg/kg for children), though most immunocompetent patients with uncomplicated disease do not require antibiotics and can be managed with observation alone. 1
When to Treat vs. Observe
Most immunocompetent patients with typical cat scratch disease (regional lymphadenopathy) do not require antibiotics and will resolve spontaneously within 1-6 months. 1, 2 However, antibiotic therapy is indicated for:
- Immunocompromised patients (especially those with CD4+ counts <100 cells/µL) 1, 3
- Extranodal or disseminated disease (hepatosplenic involvement, encephalitis, endocarditis, osteomyelitis) 1, 4
- Severe symptoms with significant systemic illness 5
- Prolonged or debilitating lymphadenopathy affecting quality of life 2
First-Line Treatment Algorithm
For Immunocompetent Patients Requiring Treatment:
Azithromycin is the only antibiotic with placebo-controlled evidence showing more rapid reduction in lymph node size: 1, 2
- Adults >45 kg: 500 mg day 1, then 250 mg daily × 4 days
- Children <45 kg: 10 mg/kg day 1, then 5 mg/kg daily × 4 days
Alternative Regimens (if azithromycin contraindicated):
For Severe or Disseminated Disease:
Doxycycline with or without rifampin is preferred for CNS involvement and other severe infections 1
Gentamicin (intramuscular/intravenous) has shown 73% efficacy and rapid response within 48 hours for severe cases with hepatosplenic involvement 5, 6
Treatment Duration by Clinical Scenario
- Uncomplicated disease: 5 days (azithromycin protocol) 1
- Immunocompromised patients with bacillary angiomatosis or peliosis hepatis: Erythromycin or doxycycline for >3 months 1, 3
- CNS bartonellosis: Extended therapy with doxycycline ± rifampin for >3 months 1
- Relapse prevention: Long-term suppression with erythromycin or doxycycline until CD4+ >200 cells/µL for >6 months 7, 3
Special Populations
Pregnant Women:
Children:
- Same treatment recommendations as adults with weight-based azithromycin dosing 1
- Fluoroquinolones should be used with extreme caution and only if no alternatives exist 7
HIV/AIDS Patients:
- More aggressive treatment required for bacillary angiomatosis 1, 3
- Consider Bartonella in any HIV patient with unexplained fever and CD4+ <100 cells/µL 1
- Up to 25% may never develop antibodies despite active infection 1
Critical Pitfalls to Avoid
Do NOT use these antibiotics - they have no clinical efficacy despite in vitro activity:
- Penicillins and first-generation cephalosporins have no in vivo activity 1, 3
- Quinolones and TMP-SMX have inconsistent clinical response and are not recommended 1, 3
Common diagnostic errors:
- Serologic testing may be negative for up to 6 weeks after infection 1
- In advanced HIV (CD4+ <100), 25% of culture-positive patients never develop antibodies 1
- Do not test cats for Bartonella - this provides no clinical benefit 1
Evidence Quality Assessment
The azithromycin recommendation is based on the only placebo-controlled trial demonstrating clinical benefit (more rapid lymph node reduction). 1, 2 However, this benefit is modest, and the majority of immunocompetent patients do not require antibiotics at all. 2
Older retrospective data from 268 patients showed rifampin (87% effective), ciprofloxacin (84% effective), and gentamicin (73% effective) had higher efficacy rates than azithromycin, but these lack controlled trial evidence. 5 The guideline preference for azithromycin reflects its superior evidence quality despite potentially lower efficacy.
For severe disease requiring hospitalization or with systemic complications, gentamicin has the strongest evidence for rapid clinical response within 48 hours. 6