Stopping IV Polymyxin Without Oral Switch
You can stop IV polymyxin after completing the appropriate treatment duration without transitioning to oral antibiotics, as there is no oral polymyxin formulation available and no guideline recommendation for oral step-down therapy after IV polymyxin treatment. 1
Why No Oral Switch is Necessary
- Polymyxins are not available in oral formulations that achieve systemic therapeutic levels for serious infections like hospital-acquired pneumonia (HAP), ventilator-associated pneumonia (VAP), or bloodstream infections 2
- The concept of "switch therapy" or "step-down therapy" applies to antibiotics that have both IV and oral formulations with adequate bioavailability (such as fluoroquinolones, linezolid, or doxycycline), which polymyxins do not 1
- Guidelines for HAP/VAP caused by carbapenem-resistant organisms recommend 7 days of IV polymyxin therapy for patients with good clinical response, with possible extension to 10-14 days for severe infections with septic shock 1, 3
Treatment Duration Before Stopping
- For HAP/VAP: Complete 7 days of IV therapy if clinical features of infection have resolved (afebrile, improving respiratory symptoms, decreasing white blood cell count) 1
- For bloodstream infections: Complete 7-14 days of IV therapy depending on source control and clinical response 1
- For severe infections with septic shock: Extend to 10-14 days of IV therapy 3
- Treatment duration should be individualized based on infection site, source control, underlying comorbidities, and initial response to therapy 1
Clinical Criteria Before Stopping Polymyxin
Ensure the patient meets these criteria before discontinuing IV polymyxin:
- Clinical stability: Resolution of fever, improvement in hemodynamics, decreasing inflammatory markers 1
- Microbiologic clearance: Negative repeat cultures if obtained 3
- Source control achieved: Drainage of abscesses, removal of infected devices if applicable 1
- Adequate treatment duration completed: Minimum 7 days for most infections, longer for complicated cases 1, 3
Critical Pitfall to Avoid
Do not attempt to switch to oral antibiotics after polymyxin therapy for systemic infections. The only scenario where oral antibiotics might be considered is if susceptibility testing reveals the organism is also susceptible to an oral agent (such as a fluoroquinolone or trimethoprim-sulfamethoxazole), in which case you would be switching to a completely different antibiotic class based on susceptibilities, not continuing polymyxin therapy orally 1
Alternative Consideration
If the organism shows susceptibility to other IV agents with oral formulations during the treatment course, consider de-escalation to a narrower-spectrum oral agent based on susceptibility results rather than continuing polymyxin 1. This would represent switching to a different antibiotic entirely, not oral polymyxin continuation.