What is the recommended treatment for Acinetobacter baumannii (A. baumannii) urinary tract infections (UTIs) with a short treatment course?

Treatment of Acinetobacter baumannii Urinary Tract Infections with Short Course Therapy

For Acinetobacter baumannii urinary tract infections, a short course treatment with sulbactam-containing regimens is recommended as first-line therapy when the isolate has MIC ≤4 mg/L due to better safety profile and efficacy compared to polymyxins. 1, 2

First-Line Treatment Options Based on Susceptibility

• For carbapenem-susceptible A. baumannii UTIs, carbapenems (imipenem, meropenem, doripenem) are recommended as drugs of choice in areas with low rates of carbapenem resistance 1
• For isolates susceptible to sulbactam (MIC ≤4 mg/L), ampicillin-sulbactam is preferred due to its better safety profile compared to polymyxins 3, 2
• For carbapenem-resistant A. baumannii (CRAB) susceptible to sulbactam, ampicillin-sulbactam remains the preferred treatment 2, 4
• For CRAB resistant to sulbactam, colistin should be used if the isolate is susceptible in vitro 2, 4

Specific Dosing Recommendations

• Ampicillin-sulbactam: Administer as a 4-hour infusion of 3g sulbactam every 8 hours (9-12g/day total) for isolates with MIC ≤4 mg/L 3, 1
• Imipenem: 0.5-1g every 6 hours (note: extended infusion not possible due to drug instability) 3
• Meropenem: 2g every 8 hours (caution: high doses associated with seizures) 3
• Colistin (Polymyxin E): Loading dose of 6-9 million IU followed by 9 million IU/day in 2-3 divided doses (with dose adjustment for renal dysfunction) 3, 1

Treatment Duration for UTIs

• While specific guidelines for short-course therapy of A. baumannii UTIs are limited, treatment can generally be completed in 7 days for uncomplicated UTIs 2
• For complicated UTIs or those with systemic symptoms, treatment should be maintained for up to 14 days 2
• Treatment duration should be guided by clinical response and resolution of symptoms 1

Special Considerations for UTIs

• Urinary catheter removal or replacement should be performed when possible, as catheterization is a risk factor for developing A. baumannii infections 3
• For uncomplicated UTIs with susceptible isolates, monotherapy is generally sufficient 1
• For complicated UTIs or those with systemic symptoms, consider combination therapy with two active agents for severe infections 1, 4

Monitoring and Adverse Effects

• Monitor renal function in patients receiving colistin, as nephrotoxicity occurs in up to 33% of patients 3, 2
• Nephrotoxicity is higher with colistin (33%) compared to ampicillin-sulbactam (15.3%) 3
• Monitor for emergence of resistance during therapy, particularly with colistin, as heteroresistance has been reported 2

Treatment Algorithm for A. baumannii UTIs

1. Obtain urine cultures and susceptibility testing before initiating therapy 1
2. Start empiric therapy based on local resistance patterns and patient risk factors 1
3. For confirmed A. baumannii UTI:
   • If carbapenem-susceptible: Use carbapenem (imipenem, meropenem) 1
   • If sulbactam-susceptible (MIC ≤4 mg/L): Use ampicillin-sulbactam (9-12g/day) 3, 2
   • If resistant to sulbactam but colistin-susceptible: Use colistin with appropriate weight-based dosing 2
   • For severe infections with systemic symptoms: Consider combination therapy with two active agents 1, 4
4. Continue treatment for 7 days for uncomplicated UTIs; up to 14 days for complicated UTIs 2

Emerging Resistance Patterns

• Regional differences in susceptibility patterns exist, with MDR rates lowest in North America (47%) and highest in Europe and the Middle East (>93%) 5
• Recent studies show decreasing susceptibility to carbapenems and piperacillin-tazobactam in A. baumannii isolates from UTIs 6
• Colistin continues to be the most active antibiotic in vitro against MDR A. baumannii from UTIs 6

Pitfalls and Caveats

• Avoid polymyxin-meropenem combination therapy for CRAB infections with high-level carbapenem resistance (MICs >16 mg/L) 4
• Avoid polymyxin-rifampin combination therapy due to lack of proven benefit 4
• Do not use carbapenems in monotherapy for severe infections in areas with high rates of resistance 1
• Be aware that dosing of colistin is complex and should be adjusted for renal function to minimize toxicity 3