What is the best antibiotic agent for treating Klebsiella variicola (K. variicola) bacteremia?

Best Antibiotic Agent for Klebsiella variicola Bacteremia

For Klebsiella variicola bacteremia, treat empirically with a carbapenem (meropenem 1g IV every 8 hours or imipenem/cilastatin 1g IV every 8 hours) as first-line therapy, then de-escalate based on susceptibility testing. 1

Initial Empiric Therapy

• Meropenem 1g IV every 8 hours is the preferred carbapenem for empiric treatment of suspected Enterobacterales bloodstream infections 1
• Imipenem/cilastatin 1g IV every 8 hours is an acceptable alternative carbapenem 1
• Carbapenems provide reliable coverage for K. variicola, which is closely related to K. pneumoniae and shares similar resistance patterns 2

If Carbapenem Resistance is Suspected or Confirmed

For carbapenem-resistant K. variicola, use ceftazidime/avibactam 2.5g IV every 8 hours as the preferred agent based on its superior activity against carbapenem-resistant Enterobacterales (CRE). 1, 3

Alternative options for carbapenem-resistant strains include:

• Meropenem/vaborbactam 4g IV every 8 hours - particularly effective against KPC-producing strains with excellent clinical outcomes (75.6% cure rate in real-world data) 1, 4, 5
• Imipenem/cilastatin/relebactam 1.25g IV every 6 hours - demonstrated non-inferiority to piperacillin/tazobactam with 15.9% mortality in critically ill patients 1, 6

Critical Decision Points

Obtain blood cultures before initiating antibiotics and perform susceptibility testing immediately to guide definitive therapy. 1

Assess illness severity using the INCREMENT score - patients with scores ≥8 have higher mortality and may benefit from combination therapy if only older agents (polymyxins, tigecycline, aminoglycosides) are available. 1

What NOT to Use

• Avoid piperacillin/tazobactam for definitive therapy even if susceptible in vitro - a landmark RCT showed 12.3% mortality with piperacillin/tazobactam versus 3.7% with meropenem for ceftriaxone-resistant Enterobacterales bacteremia (8.6% absolute risk difference). 7
• Do not use ceftriaxone or other third-generation cephalosporins as K. variicola frequently harbors ESBL genes and exhibits cross-resistance to multiple antibiotics and antiseptics. 2

Treatment Duration

• 10-14 days total for uncomplicated bacteremia 1
• Extend duration if complicated by endocarditis, osteomyelitis, or persistent bacteremia beyond 72 hours 1

Combination Therapy Considerations

For critically ill patients (septic shock, INCREMENT score ≥8) with carbapenem-resistant strains where only older agents are available, use combination therapy with two in vitro active agents - this approach reduced 30-day mortality (adjusted HR 0.56) compared to monotherapy in high-risk patients. 1

Combination options when new beta-lactam/beta-lactamase inhibitors are unavailable:

• Polymyxin-based regimens plus tigecycline, aminoglycosides, or fosfomycin 1
• High-dose extended-infusion meropenem (if MIC ≤8 mg/L) plus a second active agent 1