A 68-year-old woman with chronic kidney disease (eGFR 28 mL/min) is admitted with septic shock secondary to urinary tract infection. Urine culture grows Pseudomonas aeruginosa. Which antibiotic is the drug of choice for pseudomonal sepsis in a patient with severe renal impairment?

Explanation

## Pseudomonal Sepsis in Renal Impairment **Key Point:** Meropenem is the preferred carbapenem for pseudomonal sepsis in severe renal impairment because it maintains efficacy with dose adjustment and has superior CNS penetration compared to other agents. ### Why Meropenem Over Alternatives **High-Yield:** Carbapenems are the most reliable agents for Pseudomonas aeruginosa coverage in septic shock, especially when renal function is severely compromised. 1. **Renal Clearance & Dosing Flexibility** - Meropenem: 50% renal excretion; dose adjustment required but manageable (500 mg IV Q8H at eGFR 20–50 mL/min) - Imipenem-cilastatin: 70% renal excretion; higher seizure risk in renal failure due to cilastatin accumulation - Piperacillin-tazobactam: 68–90% renal excretion; requires significant dose reduction; less predictable in severe renal disease 2. **Pseudomonas Coverage** - Meropenem has excellent anti-pseudomonal activity - Maintains bactericidal activity even with dose adjustment - Superior CNS penetration (relevant if sepsis progresses to meningitis) **Mnemonic:** **CARB** = **C**arbapenem for **A**nti-pseudomonal **R**enal **B**ackup ### Comparison Table: Agents for Pseudomonal Sepsis | Agent | Pseudomonas Coverage | Renal Clearance | Renal Impairment Suitability | Notes | |-------|----------------------|-----------------|------------------------------|-------| | Meropenem | Excellent | 50% | **Best** | Preferred in CKD; seizure risk lower than imipenem | | Imipenem-cilastatin | Excellent | 70% | Poor | Cilastatin accumulation → seizures in renal failure | | Piperacillin-tazobactam | Excellent | 68–90% | Moderate | Requires aggressive dose reduction; less predictable | | Ceftazidime | Excellent | 80–90% | Poor | Marked renal excretion; neurotoxicity risk in renal failure | | Ciprofloxacin | Good | 40–50% | Moderate | Adequate for UTI but inferior to carbapenems in septic shock | **Clinical Pearl:** In septic shock, bactericidal agents with predictable pharmacokinetics are essential. Meropenem's lower seizure risk compared to imipenem in renal failure makes it the preferred carbapenem choice. **Warning:** Ceftazidime, while covering Pseudomonas, undergoes significant renal excretion and accumulates in severe renal impairment, increasing neurotoxicity risk. Fluoroquinolones are inadequate monotherapy for septic shock despite reasonable pseudomonal coverage. **Tip:** Always check eGFR before prescribing aminoglycosides (gentamicin, tobramycin) for pseudomonal sepsis—this patient's eGFR 28 mL/min makes aminoglycosides contraindicated due to nephrotoxicity and ototoxicity risks.