Stenotrophomonas maltophilia treatment

Why it's hard

Current guidance (IDSA 2026 AMR guidance)

• Preferred for invasive infection: cefiderocol. This rests on in vitro activity and animal models, with little clinical outcome data. It is not clearly better when used as part of a combination.
• TMP-SMX: suggested only as a component of combination therapy for invasive infection. Clinical data are limited and toxicity is well recognized (hypersensitivity, cytopenias, hepatotoxicity, renal dysfunction, GI intolerance).
• Minocycline: also suggested as part of a combination. Its serum levels are low, so it is unreliable as monotherapy for bloodstream infection. Consider switching to minocycline alone only after clear, sustained clinical improvement.
• Alternative: aztreonam-avibactam, preferably with a second agent. If it isn't available, ceftazidime-avibactam plus aztreonam is a reasonable substitute.

Textbook approach (Goldman-Cecil Medicine, older framing)

• TMP-SMX is the drug of choice at 10 to 15 mg/kg/day IV (trimethoprim component). Duration is usually 7 to 14 days, and longer for deep-seated or endovascular infection.
• If TMP-SMX-resistant (more common in cystic fibrosis):
  • Minocycline 200 mg load, then 100 to 200 mg q12h (maximum 400 mg/day).
  • Levofloxacin 750 mg daily or moxifloxacin 400 mg daily.
  • Tigecycline 200 mg load, then 100 mg q12h.
• Cefiderocol: 2 g IV q8h as a 3-hour infusion.
• Polymyxin B or colistin: an option if susceptibility is confirmed. Polymyxin B has better in vitro activity.
• Severe infection: some experts use combination therapy, such as TMP-SMX plus minocycline.
• Bloodstream infection: remove any infected device. Endocarditis may need surgery.

Practical points

• Susceptibility testing: S. maltophilia results are often unreliable or variable between methods. Confirm with the lab and your local ID service.
• Colonization: isolating it from a respiratory sample, especially in cystic fibrosis or ventilated patients, often reflects colonization. Treat only when there is clinical infection.
• Recent evidence: I found recent meta-analyses of resistance rates (2024, 2023) and a 2023 review covering cefiderocol and minocycline. I did not read them in detail, so I can't give pooled resistance figures.