Should colistin be stopped or completed for 21 days in a patient with a Candida infection who is also on amphotericin?

Colistin Management in Candida Bloodstream Infection

Stop colistin immediately—it has no activity against Candida and continuing it serves no purpose once candidemia is identified and amphotericin B has been initiated. 1

Rationale for Discontinuation

• Colistin is a polymyxin antibiotic with activity exclusively against gram-negative bacteria, particularly multidrug-resistant Pseudomonas aeruginosa and Acinetobacter baumannii, and has zero antifungal activity 2
• The typical duration of colistin therapy for gram-negative infections ranges from 5-21 days depending on clinical response, with a mean duration of 9.3 days in successful treatment of multidrug-resistant infections 2
• At day 17, if the patient has clinically responded to colistin for the original bacterial indication and repeat blood cultures now show only Candida (not the original gram-negative pathogen), there is no justification to continue colistin 2

Amphotericin B Management for Candidemia

• Amphotericin B should be continued for 14 days after the last positive blood culture result and when signs and symptoms of infection have resolved 1
• The Infectious Diseases Society of America recommends amphotericin B (0.6-1.0 mg/kg per day IV) as appropriate first-line therapy for candidemia in hemodynamically unstable patients or those with recent fluconazole exposure 1
• Amphotericin B formulations demonstrate equivalent efficacy to echinocandins for invasive candidiasis in critically ill adults, with no mortality difference between these agents 3

Critical Decision Points

• Obtain repeat blood cultures immediately to document clearance of candidemia and guide duration of antifungal therapy 1
• Remove all intravascular catheters if possible, as catheter retention significantly reduces cure rates in catheter-related candidemia 1
• If the patient had a documented gram-negative infection initially treated with colistin and is now clinically stable at day 17, discontinue colistin unless there is ongoing evidence of active gram-negative infection 2
• Consider transition from amphotericin B to fluconazole (400-800 mg/day) after clinical stabilization if the Candida species is fluconazole-susceptible, to reduce nephrotoxicity risk 1

Common Pitfalls to Avoid

• Continuing colistin "to complete 21 days" when the indication has resolved wastes resources and exposes the patient to unnecessary nephrotoxicity risk (colistin causes renal failure in approximately 9% of patients) 2
• Stopping amphotericin B prematurely before 14 days after blood culture clearance increases risk of relapse and disseminated candidiasis 1
• Failing to remove intravascular catheters in candidemia reduces treatment success rates and prolongs fungemia 1
• Not obtaining follow-up blood cultures to document clearance prevents accurate determination of amphotericin B duration 1