Does Merrem (meropenem) need to be dosed?

Meropenem Dosing Requirements

Yes, meropenem (Merrem) absolutely requires renal dose adjustment in patients with impaired kidney function, but the standard dose should be maintained at 1 gram per administration when possible, with the dosing interval extended rather than reducing individual doses below 1 gram for serious infections. 1

Standard Dosing in Normal Renal Function

• Adults should receive 500 mg IV every 8 hours for skin and skin structure infections, or 1 gram IV every 8 hours for intra-abdominal infections 2
• The infusion should be administered over 15-30 minutes, though 1 gram doses may also be given as a bolus over 3-5 minutes 2
• For infections caused by Pseudomonas aeruginosa, the dose must be increased to 1 gram every 8 hours regardless of infection type 3, 2

Critical Dosing Adjustments in Renal Impairment

The FDA label provides specific renal dosing that must be followed 2:

• CrCl >50 mL/min: Standard dose every 8 hours
• CrCl 26-50 mL/min: Standard dose every 12 hours
• CrCl 10-25 mL/min: Half the standard dose every 12 hours
• CrCl <10 mL/min: Half the standard dose every 24 hours

However, a critical pitfall exists: The Infectious Diseases Society of America advises against reducing individual doses below 1 gram when treating serious infections, even in renal impairment, and instead recommends extending the dosing interval 1. This is particularly important for organisms with MIC ≥4 mg/L, where extended infusion or continuous infusion should be considered 1.

Optimized Dosing Strategies

• Extended infusion over 3 hours is strongly recommended for critically ill patients and when treating resistant organisms with MIC ≥8 mg/L 3, 4, 5
• This strategy maximizes the time that drug concentrations remain above the MIC, which is the primary pharmacodynamic parameter correlating with efficacy 2
• For carbapenem-resistant organisms, meropenem should be combined with other agents rather than used as monotherapy 3, 5

Special Populations Requiring Dose Modification

Patients on continuous renal replacement therapy (CRRT):

• Meropenem clearance is significantly affected by hemofiltration, with 25-50% removed by CVVHF and 13-53% by CVVHDF 6
• For patients on SLED, maintain the full 1 gram dose every 12 hours rather than reducing individual doses 1
• The half-life increases from approximately 1 hour in normal renal function to 8.7 hours in anuric patients on CVVHF 7
• Critically ill anuric patients receiving CVVHF should have their dose increased by 100% to avoid underdosing 7

Pediatric patients:

• Children ≥3 months: 10-40 mg/kg every 8 hours depending on infection type (maximum 2 grams per dose) 2
• Infants <3 months: Dosing based on gestational and postnatal age, ranging from 20-30 mg/kg every 8-12 hours 2

Therapeutic Drug Monitoring Considerations

• Target trough concentrations should remain below 64 mg/L to prevent neurological toxicity, particularly in critically ill patients with renal impairment 1
• TDM is especially beneficial in critically ill patients and those with impaired renal function to guide appropriate dosing 8
• The percentage of time that unbound plasma concentrations exceed the pathogen's MIC is the key efficacy parameter 2

Duration of Therapy

• 5-7 days is the recommended duration for complicated intra-abdominal infections once adequate source control is achieved 4, 5
• 6 weeks of therapy is standard for vertebral osteomyelitis 3
• Treatment duration should be based on clinical response, source control adequacy, and inflammatory marker trends 5

Common Pitfalls to Avoid

• Never use meropenem monotherapy for polymicrobial infections like gangrenous bowel—combination therapy with anti-MRSA agents is mandatory 5
• Do not delay antibiotic administration for culture results; start empiric therapy immediately 5
• Avoid underdosing in patients on CRRT by failing to account for drug removal through hemofiltration 7, 6
• In elderly patients, dose selection must account for age-related decline in renal function 2