What is the treatment for a skin infection with greenish-yellow pus, indicative of Pseudomonas aeruginosa?

Treatment of Skin Infection with Greenish-Yellow Pus (Pseudomonas aeruginosa)

For skin infections with greenish-yellow pus indicating Pseudomonas aeruginosa, immunocompetent patients should receive oral ciprofloxacin 750 mg twice daily for 7-14 days, while immunocompromised patients or those with severe/necrotizing infections require hospitalization with intravenous combination therapy using piperacillin-tazobactam 4.5g every 6 hours plus tobramycin. 1, 2, 3, 4, 5

Initial Assessment and Risk Stratification

The first critical decision point is determining whether this is a simple skin infection in an immunocompetent host versus a severe infection requiring aggressive management:

Low-risk features (outpatient oral therapy appropriate):

• Immunocompetent host 6
• Localized infection without systemic signs 6
• No underlying diabetes, alcoholism, or immunosuppression 6
• Infections like hot tub folliculitis, toe web infection, or localized cellulitis 6

High-risk features (hospitalization with IV combination therapy required):

• Immunocompromised status (neutropenia, malignancy, HIV) 6, 7
• Diabetic or alcoholic patients 6
• Necrotizing skin and soft tissue infection 6
• Ecthyma gangrenosum or subcutaneous nodules (suggests bacteremia) 6
• Burn wound infections 6
• Systemic signs of sepsis 7

Treatment for Immunocompetent Patients (Simple Skin Infections)

Oral ciprofloxacin 750 mg twice daily for 7-14 days is the first-line treatment. 1, 3, 4, 8 The FDA label explicitly lists Pseudomonas aeruginosa as a covered pathogen for skin and skin structure infections with ciprofloxacin. 4

• The 750 mg twice-daily dose is critical—lower doses (500 mg) are insufficient for Pseudomonas coverage 1, 3
• Duration should be 7-14 days depending on severity and clinical response 1, 3
• Clinical cure with bacterial eradication occurs in approximately 75% of immunocompetent patients with skin/soft tissue Pseudomonas infections treated with ciprofloxacin monotherapy 8

Obtain wound culture before starting antibiotics to confirm susceptibility and guide therapy adjustments. 1, 3 Pseudomonas can develop resistance fairly rapidly during treatment, so culture confirmation is essential. 4

Treatment for Immunocompromised or Severe Infections

Combination IV therapy with piperacillin-tazobactam 4.5g every 6 hours PLUS tobramycin is mandatory. 2, 3, 5

Specific IV Regimen:

Primary agent: Piperacillin-tazobactam 4.5g IV every 6 hours (infused over 30 minutes) 2, 3, 5

Second agent: Tobramycin ~10 mg/kg/day IV once daily 2, 3

• Once-daily dosing is equally efficacious and less toxic than three-times-daily dosing 2, 3
• Target peak levels of 25-35 mg/mL 2, 3
• Monitor renal function and adjust dosing intervals accordingly 2, 3

Duration: 7-14 days depending on severity and clinical response 3, 5

Why Combination Therapy is Essential in High-Risk Patients:

Combination therapy with an antipseudomonal β-lactam plus an aminoglycoside delays resistance development compared to monotherapy and is recommended for severe infections, immunocompromised hosts, and necrotizing infections. 9, 1, 3 Monotherapy in compromised hosts has shown only 40% success rates with higher mortality. 8

Alternative IV Options if Piperacillin-Tazobactam Unavailable:

• Ceftazidime 2g IV every 8 hours 1, 3
• Cefepime 2g IV every 8 hours 1, 3
• Meropenem 1g IV every 8 hours 1, 3

Always combine with tobramycin or ciprofloxacin 400mg IV every 8 hours for severe infections. 3

Critical Pitfalls to Avoid:

Never use these antibiotics—they lack Pseudomonas coverage despite being "broad-spectrum":

• Ceftriaxone 3
• Cefazolin 3
• Ampicillin/sulbactam 3
• Ertapenem 3

Never underdose: Standard doses may be inadequate for P. aeruginosa; use maximum recommended doses. 1, 3

Never extend oral ciprofloxacin monotherapy beyond 14 days: This promotes resistance without proven benefit. 3

Never use aminoglycoside monotherapy: Rapid resistance emergence makes this ineffective. 2

Monitoring During Treatment:

• Obtain repeat wound culture if no clinical improvement by day 3-5 1
• Monitor for development of resistance, particularly with monotherapy 4, 8
• For aminoglycoside therapy: monitor renal function, adjust dosing, and check tobramycin levels 2, 3
• Watch for bronchospasm if nebulized antibiotics are considered (not typically used for skin infections) 9

When to Escalate Care:

Immediate surgical consultation required for:

• Necrotizing fasciitis or rapidly spreading infection 6
• Ecthyma gangrenosum (suggests bacteremia requiring blood cultures and infectious disease consultation) 6
• Burn wound infections (require specialized team) 6

Consider de-escalation to oral monotherapy once susceptibility results confirm susceptibility, patient is improving, and systemic signs have resolved. 3