What is the recommended dose of ertapenem for an adult patient with Serratia marcescens infection and impaired renal function, considering potential underlying conditions such as diabetes?

Ertapenem Dosing for Serratia marcescens in Adults with Renal Impairment

For adult patients with Serratia marcescens infection and impaired renal function, administer ertapenem 500 mg once daily if creatinine clearance is ≤30 mL/min/1.73 m², with a supplementary 150 mg dose if given within 6 hours before hemodialysis. 1

Standard Dosing in Normal Renal Function

• For adults with normal renal function (creatinine clearance >90 mL/min/1.73 m²), the standard ertapenem dose is 1 gram once daily administered intravenously over 30 minutes 1
• Treatment duration varies by infection type: 5-14 days for complicated intra-abdominal infections, 7-14 days for complicated skin/soft tissue infections including diabetic foot infections, and 10-14 days for complicated urinary tract infections 1
• Ertapenem demonstrates excellent activity against Serratia marcescens, with imipenem (the carbapenem class) showing universal susceptibility in clinical isolates 2

Renal Dose Adjustments

For patients with severe renal impairment (creatinine clearance ≤30 mL/min/1.73 m²) and end-stage renal disease (creatinine clearance ≤10 mL/min/1.73 m²), reduce the dose to 500 mg once daily. 1

• No dosage adjustment is necessary when creatinine clearance exceeds 30 mL/min/1.73 m² 1
• Dosing modifications are not required based on gender, age, weight, or liver disease in adults 3

Hemodialysis-Specific Considerations

Critical timing issue: If ertapenem is administered within 6 hours prior to hemodialysis, give a supplementary dose of 150 mg following the dialysis session 1

• Approximately 30% of ertapenem is cleared during a hemodialysis session 4
• If ertapenem is given at least 6 hours before hemodialysis, no supplementary dose is needed 1
• Major pitfall: The recommended 500 mg daily dose may still pose risk for CNS toxicity (seizures, hallucinations, cognitive dysfunction) in regular hemodialysis patients, particularly those with smaller body size 4

Special Considerations for Diabetic Patients

• Diabetic patients with Serratia marcescens infections often have severe underlying disease and higher mortality risk 2
• For diabetic foot infections specifically, ertapenem 1 gram daily (or 500 mg if CrCl ≤30) is appropriate, with treatment duration of 7-14 days 5, 1
• Ertapenem provides adequate coverage for polymicrobial infections common in diabetic foot infections, though it lacks activity against Pseudomonas aeruginosa 5

Antimicrobial Susceptibility Context

• Serratia marcescens demonstrates increasing multidrug resistance, but carbapenems (including ertapenem) maintain excellent activity 2
• All Serratia isolates are universally resistant to ampicillin and first-generation cephalosporins 2
• Imipenem shows MIC₉₀ of 1.0 μg/mL against Serratia marcescens, indicating reliable carbapenem efficacy 2
• Emerging concern: KPC-2 carbapenemase-producing Serratia marcescens strains have been reported, though this remains uncommon 6

Administration Guidelines

• Administer intravenously over 30 minutes 1
• Do not mix or co-infuse with other medications 1
• Do not use diluents containing dextrose 1
• Complete infusion within 6 hours of reconstitution 1

Monitoring for CNS Toxicity in Dialysis Patients

High alert: Watch for unexplained seizures, hallucinations, or cognitive dysfunction after 3-7 consecutive doses in hemodialysis patients 4

• CNS toxicity symptoms typically resolve within 8 days after discontinuation 4
• Plasma ertapenem accumulation occurs with consecutive dosing in dialysis patients despite dose reduction 4
• Consider even lower doses or alternative agents if CNS symptoms develop 4