Orbital cellulitis is considered an ophthalmologic emergency. The mainstay of therapy for orbital cellulitis involves prompt intravenous antimicrobial therapy with either beta-lactams or clindamycin. Patients suspected to have MRSA-induced orbital cellulitis require more extensive antimicrobial therapy.

• 1. Causative pathogens

• Methicillin-sensitive staphylococcus aureus
• Methicillin-resistant staphylococcus aureus
• Staphylococcus epidermidis
• Streptococcus spp.
• Moraxella spp.
• Anaerobes

• 2. Empiric antimicrobial therapy

• Preferred regimen (1): Ampicillin/Sulbactam 3 g IV q6h for 1 week
• Preferred regimen (2): Ceftriaxone 1-2 g IV q12h for 1 week
• Preferred regimen (3): Clindamycin 300 mg IV q6h for 1 week
• Preferred regimen (4): Nafcillin 2 g IV q4h for 1 week AND Ceftriaxone 2 g IV q24h for 1 week AND Metronidazole 30-35 mg/kg/d IV divided in 3 doses for 1 week
• Alternative regimen (1), MRSA suspicion: Vancomycin 1 g IV q12h for 1 week AND Ceftriaxone 2 g IV q24h for 1 week AND Metronidazole 30-35 mg/kg/d IV divided q8h for 1 week
• Alternative regimen (2), MRSA suspicion: Vancomycin 1 g IV q12h for 1 week AND Levofloxacin 750 mg IV q24h for 1 week AND Metronidazole 30-35 mg/kg/d IV divided q8h for 1 week
• Alternative regimen (3), pediatric: Ampicillin/Sulbactam 200-300 mg/kg/d IV divided q6h for 1 week
• Alternative regimen (4), pediatric: Ceftriaxone 100 mg/kg/d IV divided q12h for 1 week
• Alternative regimen (5), pediatric: Clindamycin 20-40 mg/kg/d IV divided q12 for 1 week
• Note (1): Oral antibiotic therapy may be extended beyond 2-3 weeks if the clinical presentation is consistent with either severe sinusitis or bony destruction
• Note (2): Consider surgical intervention if the patient has either visual loss, complete ophthalmoplegia, large abscess > 1 cm, or no clinical improvement following 1-2 days of antibiotic administration

• 3. Pathogen-directed antimicrobial therapy

• 3.1 Methicillin-resistant staphylococcus aureus (MRSA)

• Preferred regimen (1): Vancomycin 1 g IV q12h for 1 week AND Ceftriaxone 2 g IV q24h for 1 week AND Metronidazole 30-35 mg/kg/d IV divided q8h for 1 week
• Preferred regimen (2): Vancomycin 1 g IV q12h for 1 week AND Levofloxacin 750 mg IV q24h for 1 week AND Metronidazole 30-35 mg/kg/d IV divided q8h for 1 week

• 3.2 Non-MRSA organisms

• Preferred regimen (1): Ampicillin/Sulbactam 3 g IV q6h for 1 week
• Preferred regimen (2): Ceftriaxone 1-2 g IV q12h for 1 week
• Preferred regimen (3): Clindamycin 300 mg IV q6h for 1 week
• Preferred regimen (4): Nafcillin 2 g IV q4h for 1 week AND Ceftriaxone 2 g IV q24h for 1 week AND Metronidazole 30-35 mg/kg/d IV divided in 3 doses for 1 week