What is the treatment for a patient with Acinetobacter baumannii in their urine culture?

Treatment of Acinetobacter baumannii in Urine Culture

For A. baumannii urinary tract infections, use carbapenems (imipenem, meropenem, or doripenem) as first-line therapy if the isolate is carbapenem-susceptible, or ampicillin-sulbactam (9-12g/day in divided doses) if the isolate has a sulbactam MIC ≤4 mg/L, with treatment duration of 7 days for uncomplicated UTIs and up to 14 days for complicated cases. 1

Initial Management and Culture-Directed Therapy

• Obtain cultures and susceptibility testing before initiating therapy to guide definitive treatment decisions 2
• Remove or replace urinary catheters when possible, as catheterization is a major risk factor for A. baumannii UTI development 1
• Start empiric therapy based on local resistance patterns while awaiting susceptibility results 2

Treatment Selection Based on Susceptibility

For Carbapenem-Susceptible Isolates (in areas with low resistance rates)

• Carbapenems are the drugs of choice: imipenem 0.5-1g every 6 hours OR meropenem 2g every 8 hours 3, 1
• This recommendation applies only in geographic areas with low rates of carbapenem resistance 3
• Monotherapy is generally sufficient for uncomplicated UTIs with susceptible isolates 1

For Sulbactam-Susceptible Isolates (MIC ≤4 mg/L)

• Ampicillin-sulbactam is preferred over polymyxins due to superior safety profile, particularly lower nephrotoxicity (15.3% vs 33%) 3, 1
• Dosing: Administer as a 4-hour infusion of 3g sulbactam every 8 hours (total 9-12g/day) 3, 1
• Sulbactam has intrinsic bactericidal activity against A. baumannii independent of its β-lactamase inhibitor properties 3

For Carbapenem-Resistant Isolates

• Colistin (polymyxin E) is the treatment of choice if the isolate is susceptible in vitro 4, 1
• Dosing: Loading dose of 6-9 million IU, followed by 9 million IU/day in 2-3 divided doses 1
• Mandatory dose adjustment for renal dysfunction is required 1
• Monitor renal function closely, as nephrotoxicity occurs in up to 33% of patients receiving colistin 3, 1

Treatment Duration

• Uncomplicated UTIs: 7 days of therapy is generally sufficient 1
• Complicated UTIs or those with systemic symptoms: Extend treatment to 14 days 1
• Guide duration by clinical response and resolution of symptoms 1

Combination Therapy Considerations

• For uncomplicated UTIs with susceptible isolates, monotherapy is adequate 1
• For complicated UTIs with systemic symptoms or severe infections, consider combination therapy with two active agents 2, 1
• Avoid colistin plus rifampin: This combination lacks proven benefit 1
• Avoid colistin plus glycopeptides (vancomycin): This increases nephrotoxicity without added benefit 3, 1

Critical Pitfalls to Avoid

• Never use carbapenems in monotherapy for severe infections in areas with high carbapenem resistance rates (>25% resistance) 3, 2
• Never use tigecycline as monotherapy for bacteremia due to suboptimal serum concentrations, though this is less relevant for UTIs where urinary concentrations may be adequate 2, 5
• Never use ertapenem for A. baumannii infections as it lacks activity against this pathogen 2
• Do not delay appropriate therapy in critically ill patients with known A. baumannii colonization 2

Monitoring Requirements

• Monitor renal function throughout treatment, especially with colistin therapy 1
• Assess clinical response and consider repeat urine cultures to document clearance 2
• Be vigilant for emergence of resistance during therapy, particularly with colistin, as heteroresistance has been reported 4
• Watch for development of tigecycline resistance in A. baumannii during standard treatment courses, which appears attributable to MDR efflux pump mechanisms 5