What are the recommended antibiotics for treating Acinetobacter Baumannii infections according to Infectious Diseases Society of America (IDSA) guidelines?

Treatment of Carbapenem-Resistant Acinetobacter baumannii (CRAB) Infections

For carbapenem-resistant A. baumannii infections, use colistin (polymyxin E) with a loading dose of 5 mg CBA/kg IV followed by 2.5 mg CBA × (1.5 × CrCl + 30) IV every 12 hours, combined with either high-dose carbapenem (imipenem 500 mg IV q6h or meropenem 2g IV q8h infused over >3 hours) if carbapenem MIC ≤32 mg/L, or alternatively combine colistin with high-dose sulbactam (6-9 g/day IV in 3-4 divided doses) plus tigecycline (100 mg IV loading, then 50 mg IV q12h). 1

Treatment Algorithm by Infection Site

For CRAB Pneumonia (First-Line)

• Administer IV colistin with loading dose of 5 mg CBA/kg, then maintenance of 2.5 mg CBA × (1.5 × CrCl + 30) every 12 hours 1
• Add high-dose carbapenem (imipenem 500 mg IV q6h OR meropenem 2g IV q8h) if carbapenem MIC ≤32 mg/L, infused over >3 hours for synergistic benefit 1
• Add adjunctive inhaled colistin 1.25-15 MIU/day in 2-3 divided doses 1
• Continue for at least 7 days 1

For CRAB Pneumonia (Alternative Regimen)

• High-dose sulbactam monotherapy: 6-9 g/day IV in 3-4 divided doses as 4-hour infusions 1, 2
• OR triple combination: colistin (dosed as above) + tigecycline (100 mg IV loading, then 50 mg IV q12h) + sulbactam (6-9 g/day) 1
• Critical caveat: Never use tigecycline as monotherapy for pneumonia 1, 3

For CRAB Bloodstream Infections

• IV colistin with same dosing as pneumonia (loading 5 mg CBA/kg, then maintenance based on renal function) 1
• Add high-dose carbapenem if MIC ≤32 mg/L (same dosing as pneumonia) 1
• Alternative: colistin + tigecycline (if tigecycline MIC ≤2 mg/L) OR colistin + sulbactam 1
• Duration: 10-14 days 1
• Critical caveat: Never use tigecycline monotherapy for bacteremia due to suboptimal serum concentrations 3

For CRAB Urinary Tract Infections

• For sulbactam-susceptible isolates (MIC ≤4 mg/L): ampicillin-sulbactam 3g sulbactam every 8 hours as 4-hour infusion (9-12g/day total) 2
• For sulbactam-resistant isolates: colistin with loading dose 6-9 million IU, then 9 million IU/day in 2-3 divided doses, adjusted for renal dysfunction 2
• Duration: 7 days for uncomplicated UTIs, up to 14 days for complicated UTIs 2
• Remove or replace urinary catheter when possible 2

Treatment Selection Based on Susceptibility Testing

If Carbapenem-Susceptible A. baumannii

• Use carbapenems (imipenem, meropenem, or doripenem) as first-line in areas with low carbapenem resistance 3, 4
• Ertapenem has NO activity against A. baumannii and must never be used 3
• Do not use carbapenem monotherapy for severe infections in areas with high resistance rates (>25%) 3

If Sulbactam-Susceptible (MIC ≤4 mg/L)

• Ampicillin-sulbactam is preferred over polymyxins due to better safety profile 2, 5
• Dose: 3g sulbactam every 8 hours as 4-hour infusion (9-12g/day total) 2, 5
• Nephrotoxicity rate: 15.3% vs 33% with colistin 5

If Only Colistin-Susceptible

• Reserve colistin for strains resistant to both carbapenems and sulbactam 5
• Use weight-based dosing adjusted for renal function 3

Combination Therapy Considerations

Recommended Combinations

• Colistin + carbapenem (if carbapenem MIC ≤32 mg/L) for severe infections 1, 3
• Colistin + sulbactam + tigecycline for clinical failures or high MIC isolates 1, 3
• Combination therapy with two active agents is recommended for severe CRAB infections, especially septic shock 3

Combinations to AVOID

• Never combine colistin + rifampin (lacks proven benefit) 3, 5
• Never combine colistin + vancomycin or other glycopeptides (increased nephrotoxicity without benefit) 3, 5
• Never use polymyxin-meropenem for high-level carbapenem resistance (MIC >16 mg/L) 2, 3

Critical Monitoring Requirements

Nephrotoxicity Surveillance

• Monitor renal function closely in all patients receiving colistin 2, 5
• Nephrotoxicity occurs in up to 33% of colistin-treated patients vs 15.3% with sulbactam 5
• Adjust colistin dosing for renal dysfunction using the formula: 2.5 mg CBA × (1.5 × CrCl + 30) IV q12h 1

Treatment Response Assessment

• Obtain cultures and susceptibility testing before initiating therapy 3
• Consider repeat blood cultures to document clearance in bacteremia 3
• Maintain therapy for 2 weeks for severe infections (VAP, bacteremia with septic shock) 3

Common Pitfalls to Avoid

• Do not underdose sulbactam - use 9-12 g/day for severe infections, not standard doses 5
• Do not delay appropriate therapy in critically ill patients with known CRAB colonization or during outbreaks 3
• Do not use carbapenems alone for severe infections in high-resistance areas 3
• Do not ignore local resistance patterns when selecting empiric therapy 5, 6
• Do not use ertapenem - it completely lacks activity against A. baumannii 3