What are the guidelines for using colistin (polymyxin E) injection for treating surgical site infections?

Colistin for Surgical Site Infections: Evidence-Based Guidelines

Colistin injection is NOT a standard or recommended antibiotic for surgical site infections according to current guidelines; it should be reserved exclusively as a last-resort agent for multidrug-resistant gram-negative infections when all other antibiotics have failed. 1, 2, 3

Standard SSI Management Does Not Include Colistin

The cornerstone of SSI treatment is immediate surgical drainage, with antibiotic selection based on the surgical site and expected pathogens 1, 3:

First-Line Antibiotic Choices for SSIs

For non-intestinal incisional SSIs:

• Trunk/extremities: Oxacillin or first-generation cephalosporins 1
• Axilla/perineum: Cefoxitin or ampicillin-sulbactam 1

For necrotizing infections:

• Broad-spectrum regimens: Piperacillin-tazobactam, ciprofloxacin, or meropenem plus clindamycin or metronidazole 1, 2

For empirical coverage of mixed flora:

• Amoxicillin-clavulanate, piperacillin-tazobactam, or ceftriaxone plus metronidazole 3

When Colistin May Be Considered (Salvage Therapy Only)

Colistin is FDA-approved for gram-negative infections caused by susceptible organisms, specifically Pseudomonas aeruginosa, Enterobacter aerogenes, Escherichia coli, and Klebsiella pneumoniae 4. However, it is NOT indicated for routine SSI treatment.

Specific Indications for Colistin in SSI Context

Reserve colistin exclusively for:

• Documented multidrug-resistant (MDR) gram-negative SSIs with no other treatment options 5, 6
• Pathogens resistant to all beta-lactams, fluoroquinolones, and aminoglycosides 5, 7
• Culture-proven Acinetobacter baumannii, P. aeruginosa, or K. pneumoniae resistant to carbapenems 5, 6

Clinical Evidence for Colistin in SSI

In a retrospective study of 60 patients with MDR gram-negative infections, only 6.6% had surgical site infections, with a 71.7% favorable response rate when colistin was used 5. One case report documented successful treatment of post-neurosurgical SSI with MRAB using intravenous colistin combined with ceftazidime and rifampicin 8.

Dosing Guidelines When Colistin Is Necessary

Standard dosing (from FDA label):

• 2.5 to 5 mg/kg/day of colistin base activity divided into 2-4 doses for patients with normal renal function 4
• Base dosing on ideal body weight in obese patients 4

Intravenous administration options:

• Direct intermittent: One-half total daily dose over 3-5 minutes every 12 hours 4
• Continuous infusion: One-half as bolus, remainder infused over 22-23 hours 4

Renal dose adjustments (critical):

• Creatinine clearance 50-79 mL/min: 2.5-3.8 mg/kg divided into 2 doses 4
• Creatinine clearance 30-49 mL/min: 2.5 mg/kg once daily or divided into 2 doses 4
• Creatinine clearance 10-29 mL/min: 1.5 mg/kg every 36 hours 4

Combination Therapy Is Essential

Never use colistin as monotherapy for serious infections 5, 7:

• 87% of patients in clinical studies received combination therapy 5
• Combine with beta-lactams, aminoglycosides, or fluoroquinolones based on susceptibility testing 5, 6
• For neurosurgical SSI with MRAB, consider adding rifampicin based on synergy testing 8

Critical Safety Considerations

Nephrotoxicity Risk

• Occurs in 10.9% of patients, primarily those with pre-existing renal impairment 5
• Monitor renal function closely, especially when combining with aminoglycosides (used in 48% of cases) 5, 7
• Nephrotoxicity is generally reversible 5, 7

Neurotoxicity

• Rare but documented 7, 9
• Monitor for paresthesias, vertigo, and neuromuscular blockade 7

Common Pitfalls to Avoid

Do not use colistin empirically for SSIs - Standard guidelines recommend oxacillin, cephalosporins, or beta-lactam/beta-lactamase inhibitor combinations first 1, 3

Do not delay surgical drainage - Opening and draining infected wounds is the single most important intervention; antibiotics alone (including colistin) are insufficient 3

Do not ignore culture and susceptibility testing - Colistin should only be used after documented resistance to standard agents 1, 4, 5

Do not use suboptimal doses - Underdosing has been linked to resistance development 7, 9

Do not forget renal dose adjustments - Failure to adjust for renal function increases toxicity risk significantly 4, 9

Resistance Concerns

Colistin resistance is emerging among Acinetobacter, Pseudomonas, and Klebsiella species 8, 7. MIC values ≥2 µg/mL indicate reduced susceptibility 8. This underscores the critical importance of reserving colistin for true salvage situations only.