What are the recommended doses of imipenem‑cilastatin for adults and children, and how should they be adjusted for renal impairment?

Imipenem-Cilastatin Dosing

Standard Adult Dosing (Normal Renal Function)

For adults with creatinine clearance ≥90 mL/min, administer 500 mg every 6 hours or 1000 mg every 8 hours, with a maximum daily dose of 4 grams. 1

• These regimens provide adequate coverage for most susceptible organisms in patients with preserved renal function 1
• The drug must be given as intermittent infusions prepared immediately before administration due to chemical instability (stable only 2-3 hours in 0.9% NaCl at 25°C) 1
• Prolonged continuous infusion is not appropriate for imipenem-cilastatin 1

Critically Ill Patients

Administer a loading dose equal to the intended maintenance dose (500 mg or 1000 mg) before starting intermittent therapy in critically ill patients, regardless of renal function. 1

• This compensates for the increased volume of distribution seen in sepsis 1
• Standard maintenance dosing (500 mg every 6 hours or 1000 mg every 8 hours) should follow the loading dose 1

Pediatric Dosing

Administer 100 mg/kg/day total dose for children up to 3 years of age and 60 mg/kg/day for children over 3 years of age. 2

• This dosing has demonstrated favorable clinical response in 98% of evaluable pediatric patients 2
• The safety profile in children is comparable to other beta-lactam antibiotics, with mild and reversible adverse effects 2

Renal Impairment Dosing

Mild Renal Impairment (CrCl 60-89 mL/min)

• Plasma exposure increases by approximately 1.6-fold for both imipenem and relebactam 3
• Dose reduction is recommended per FDA labeling 4

Moderate Renal Impairment (CrCl 30-59 mL/min)

• Plasma exposure increases further, requiring additional dose adjustment 3
• Consult FDA prescribing information for specific dose modifications 4

Severe Renal Impairment (CrCl <30 mL/min)

Limit maximum dose to either 1000 mg twice daily or 500 mg four times daily in patients with creatinine clearance <15 mL/min. 5

• Imipenem half-life increases from 52 minutes (normal function) to 173 minutes in end-stage renal disease 5
• Cilastatin half-life increases dramatically from 54 minutes to 798 minutes in end-stage renal disease, necessitating dose reduction to prevent accumulation 5
• Twice-daily dosing of 500 mg maintains therapeutic plasma levels (≥4 mg/L) for 8-10 hours and is well tolerated 6

Hemodialysis Patients

Administer a supplemental 500 mg dose after each dialysis session. 5, 7

• Both imipenem and cilastatin are efficiently removed by hemodialysis 5, 7
• Dialysis reduces imipenem half-life from 4.80 to 2.45 hours and cilastatin half-life from 16.63 to 3.86 hours 8
• Without supplemental dosing, therapeutic levels will be inadequate 7

Augmented Renal Clearance (ARC)

For critically ill patients with CrCl ≥130 mL/min, use standard dosing of 1.25 g every 6 hours as a 30-minute infusion. 9

• Despite enhanced clearance of both imipenem and relebactam in ARC, standard dosing achieves 100% probability of target attainment at MIC ≤1 mg/L and 93% at MIC 2 mg/L 9
• Clinical response rates are higher with imipenem-cilastatin-relebactam (91.7%) versus piperacillin-tazobactam (44.4%) in patients with CrCl ≥250 mL/min 10
• No dose increase is required for ARC patients 9

Key Clinical Considerations

Chemical Stability

• Prepare solutions immediately before infusion 1
• Do not use for continuous infusion protocols 1

Renal Function Monitoring

• Assess creatinine clearance at baseline and adjust doses accordingly 4
• Monitor renal function during therapy, particularly in patients with baseline impairment 3
• The dose fraction excreted in urine decreases progressively with worsening renal impairment 3

Drug Interactions

• Probenecid reduces renal clearance of imipenem by 31% but has no clinically meaningful impact requiring dose adjustment 3
• Avoid concomitant use with valproic acid due to increased seizure risk 4