Treatment of Acinetobacter Infections

First-Line Treatment Options

• For susceptible strains, sulbactam is the preferred treatment option due to its intrinsic activity against A. baumannii and better safety profile compared to colistin 1, 2, 3
• In areas with low carbapenem resistance, carbapenems remain the drugs of choice for A. baumannii infections 4, 3
• For carbapenem-resistant A. baumannii susceptible to sulbactam, ampicillin-sulbactam should be used as first-line therapy 5
• Colistin should be reserved for strains resistant to both carbapenems and sulbactam to preserve its effectiveness and avoid unnecessary toxicity 1, 2

Comparative Efficacy and Safety

• Clinical studies comparing sulbactam and colistin for MDR A. baumannii ventilator-associated pneumonia have shown comparable clinical and microbiological response rates 1, 2
• Nephrotoxicity rates are significantly higher with colistin (33%) compared to sulbactam (15.3%) 1, 2
• A retrospective study of patients with carbapenem-resistant A. baumannii VAP found similar clinical cure rates between sulbactam and colistin groups, but microbiological cure rates at day 7 were significantly lower in the colistin group 1, 2
• Impairment of renal function and 30-day mortality were significantly higher in patients treated with colistin compared to sulbactam 1, 2

Dosing Recommendations

• For severe A. baumannii infections, high-dose sulbactam therapy at 9-12 g/day divided into 3 daily doses is recommended 1, 2, 6
• A 4-hour infusion is suggested for each sulbactam dose to optimize pharmacokinetic/pharmacodynamic properties 2, 6
• For colistin, when necessary, a loading dose of 6-9 million IU followed by 9 million IU/day in 2-3 doses is recommended, with dose adjustment for renal function 2, 3

Combination Therapy Considerations

• There are no convincing data to recommend combination therapy over monotherapy for directed treatment of A. baumannii infections 7
• The routine combination of colistin plus rifampin is not recommended 7
• Combination of colistin with anti-Gram-positive agents is discouraged due to increased nephrotoxicity 7, 5
• For clinical failures or infections with isolates having MICs at the upper limit of susceptibility, combination of sulbactam or polymyxin with a second agent may be considered 7

Clinical Algorithm for Treatment Selection

• Obtain cultures and susceptibility testing before initiating therapy 5
• For empiric therapy in patients with risk factors for A. baumannii infection, use a carbapenem in areas with low carbapenem resistance, and consider a polymyxin in areas with high carbapenem resistance 4, 3
• For directed therapy based on susceptibility results, use ampicillin-sulbactam for strains susceptible to sulbactam, and colistin for strains resistant to sulbactam but susceptible to colistin 1, 2, 6, 5

Common Pitfalls and Considerations

• Underdosing sulbactam may be insufficient for severe infections 6
• Not considering local resistance patterns and MIC values when selecting therapy 6, 5
• Heteroresistance to colistin is a concern, with rates varying from 18.7% to 100% in clinical isolates 4
• Previous use of colistin might be a risk factor for higher rates of heteroresistance 4
• Monitor renal function closely in patients receiving colistin, as nephrotoxicity occurs in up to 33% of patients 1, 2, 5

Management of Carbapenem‑Resistant Acinetobacter baumannii (CRAB) with Ampicillin‑Sulbactam MIC ≥ 32 µg/mL

Efficacy of Ampicillin‑Sulbactam

Guideline recommendation based on pharmacodynamic data

Primary Antimicrobial Therapy

Polymyxin B as the cornerstone agent

Combination Therapy Considerations

Adjunct agents to enhance efficacy or address resistance

Safety and Monitoring

Key adverse‑effect surveillance

Efficacy of Newer β‑lactam/β‑lactamase Inhibitor Combinations and Aminoglycosides for Acinetobacter baumannii Urinary Tract Infections

Agents Not Recommended for Acinetobacter baumannii UTI

• Ceftazidime‑avibactam, meropenem‑vaborbactam, and imipenem‑cilastatin‑relebactam demonstrate activity against carbapenem‑resistant Enterobacteriaceae but lack activity against carbapenem‑resistant Acinetobacter baumannii (CRAB). Consequently, these agents are not recommended for treating A. baumannii urinary tract infections. 9

Limited Evidence for Aminoglycosides in Acinetobacter baumannii UTI

• Plazomicin and other aminoglycosides may exhibit variable in‑vitro activity against A. baumannii, but current evidence is insufficient to support their routine use for A. baumannii urinary tract infections. 9

Antibiotic Management of Acinetobacter baumannii Infections in Hemodialysis Patients

Timing of β‑lactam Therapy

• Administer ampicillin‑sulbactam immediately after each hemodialysis session to maximize drug exposure, since both ampicillin and sulbactam are dialyzable. 10

Use of Polymyxins (Colistin)

• Reserve colistin only for isolates resistant to all β‑lactams, fluoroquinolones, and tigecycline; it is not indicated for pan‑susceptible A. baumannii. 11, 10
• For intermittent hemodialysis patients who require colistin, give 2 million IU of colistimethate sodium every 12 hours with a loading dose of 6–9 million IU, scheduling dialysis toward the end of the dosing interval. 11, 10, 12

Polymyxin B Dosing Considerations

• Use a loading dose of 2–2.5 mg/kg of polymyxin B followed by a maintenance dose of 1.5–3 mg/kg per day; no dose adjustment is needed for hemodialysis. 10, 12

Tigecycline Use in Bacteremia

• Avoid tigecycline monotherapy for A. baumannii bacteremia because of low serum concentrations and documented poor clinical outcomes. 11, 12

Carbapenem Dosing Adjustments for Hemodialysis

• When a carbapenem is selected, administer supplemental doses after each dialysis session to maintain therapeutic drug levels. 10