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CRAB Pneumonia Colistin Combination — SCE Infectious Diseases MCQ

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HardAntimicrobial StewardshipCRAB Pneumonia Colistin CombinationSCE Infectious Diseases

A 55-year-old man develops hospital-acquired Acinetobacter baumannii pneumonia. The organism is resistant to Meropenem (MIC >16 mg/L) and sensitive only to Colistin and Tigecycline. What combination is recommended for carbapenem-resistant A. baumannii (CRAB) pneumonia?

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Correct answer: D — IV Colistin (Colistimethate sodium — loading dose then maintenance) PLUS IV Meropenem at extended infusion (despite in vitro resistance — potential synergy at high-dose extended infusion) ± inhaled Colistin for additional pulmonary delivery

CRAB pneumonia has limited treatment options. Current evidence supports: (1) IV Colistin (Colistimethate sodium — 9 MU loading dose then 4.5 MU BD) as the backbone, (2) high-dose IV Meropenem at extended infusion (despite in vitro resistance — in vitro synergy with Colistin has been demonstrated and clinical benefit suggested in observational studies), (3) adjunctive inhaled Colistin (nebulised Colistimethate 2–4 MU BD) to achieve high pulmonary concentrations. Tigecycline has suboptimal pulmonary PK and should NOT be used as monotherapy for pneumonia. Cefiderocol is an emerging option for CRAB.

Reference: BSAC 2023 – CRAB treatment; EUCAST 2024; IDSA 2023 – CRO guidance