What empiric antibiotic regimen should be used for a patient with carbapenem‑resistant Acinetobacter baumannii and methicillin‑resistant Staphylococcus haemolyticus isolated from a positive endotracheal aspirate and wound culture?

The culture shows a carbapenem‑resistant Acinetobacter baumannii (CRAB) together with Staphylococcus haemolyticus from a positive endotracheal aspirate and a wound specimen, so both a ventilator‑associated pneumonia/respiratory infection and a wound infection must be covered. Because CRAB is usually only susceptible to polymyxins, high‑dose sulbactam, tigecycline, minocycline or the newer agent cefiderocol, and S haemolyticus is typically methicillin‑resistant and requires a drug active against coagulase‑negative staphylococci, the safest empiric regimen is a combination that covers both organisms:

1. IV colistin (polymyxin E) – give a loading dose of 9 million IU (≈300 mg colistin base activity) over 30 minutes, then 4.5 million IU every 12 hours (adjust for renal function).
2. IV ampicillin‑sulbactam – 12 g per day divided q6 h (3 g every 6 h) if the isolate is reported susceptible to sulbactam; this adds synergistic activity against Acinetobacter.
3. IV tigecycline – 100 mg loading dose, then 50 mg every 12 hours (use only if the Acinetobacter is reported susceptible; tigecycline penetrates lung tissue well).
4. IV vancomycin – 15 mg/kg every 12 hours (target trough 15–20 µg/mL) to treat the S haemolyticus, which is usually resistant to β‑lactams. If vancomycin cannot be used (e.g., renal failure), replace with linezolid 600 mg IV/PO every 12 hours.

Give the combination for 7–14 days, tailoring the exact duration to clinical response, source control, and repeat cultures. If susceptibility testing shows the Acinetobacter is susceptible to cefiderocol, replace colistin plus tigecycline with cefiderocol 2 g IV every 8 hours (adjust for renal function). If the isolate is susceptible to minocycline, an alternative to tigecycline is minocycline 100 mg IV/PO every 12 hours.

In addition to antimicrobials, ensure aggressive wound care with debridement, appropriate dressing changes, and removal of any foreign material if possible. Monitor renal function, electrolytes, and drug levels (vancomycin troughs, colistin levels if available) closely, and adjust doses as needed. This regimen provides broad, synergistic coverage for both the carbapenem‑resistant Acinetobacter and the methicillin‑resistant Staphylococcus haemolyticus while allowing for de‑escalation once definitive susceptibilities are known.