Meropenem Dosing for E. coli UTI in 80-Year-Old with GFR 51 mL/min
For this 80-year-old man with E. coli urinary tract infection and GFR 51 mL/min, meropenem should be dosed at 500 mg IV every 12 hours (for complicated skin/soft tissue infections) or 1 gram IV every 12 hours (for intra-abdominal infections), based on the FDA-approved renal dosing adjustment for creatinine clearance 26-50 mL/min. 1
Renal Dose Adjustment Algorithm
The FDA prescribing information provides clear guidance for meropenem dosing in renal impairment 1:
- GFR >50 mL/min: Standard dose (500 mg or 1 gram depending on infection) every 8 hours
- GFR 26-50 mL/min: Recommended dose every 12 hours (your patient falls here)
- GFR 10-25 mL/min: One-half recommended dose every 12 hours
- GFR <10 mL/min: One-half recommended dose every 24 hours
Specific Dosing for UTI Context
For urinary tract infections specifically, the appropriate meropenem dose depends on infection severity 1:
- If treating as complicated UTI/pyelonephritis: Use 1 gram IV every 12 hours (adjusted from standard 1 gram every 8 hours)
- If Pseudomonas aeruginosa is suspected or confirmed: The standard recommendation is 1 gram every 8 hours, which should be adjusted to 1 gram every 12 hours for GFR 26-50 mL/min 1
Each dose should be administered as an IV infusion over 15-30 minutes 1.
Critical Considerations for This Patient
Age-related factors: At 80 years old, this patient likely has age-related decline in renal function beyond the measured GFR 2. The Cockcroft-Gault formula (which the FDA dosing is based on) accounts for age, but actual drug clearance may be further reduced 2.
E. coli susceptibility: While E. coli is typically susceptible to carbapenems, local resistance patterns should guide therapy 3. For ESBL-producing E. coli causing UTI, meropenem remains an excellent choice 3.
Monitoring requirements: In patients with renal dysfunction, thrombocytopenia has been observed with meropenem 1. Monitor complete blood counts during therapy, particularly if treatment extends beyond 7-10 days.
Common Pitfalls to Avoid
- Do not use standard dosing: Failure to adjust for renal function risks drug accumulation and increased adverse effects, particularly CNS toxicity including seizures 1
- Verify creatinine clearance calculation: Ensure GFR/CrCl was calculated using Cockcroft-Gault formula, as this is what FDA dosing tables are based on 1, 2
- Avoid underdosing: Do not reduce the individual dose amount when GFR is 26-50 mL/min—only extend the interval to every 12 hours 1
- Consider drug interactions: If the patient is on valproic acid or divalproex sodium, meropenem significantly reduces valproic acid levels and increases seizure risk 1
Alternative Considerations
If meropenem is being considered for a simple E. coli cystitis (which would be unusual), other agents with better oral bioavailability and simpler dosing would be more appropriate, such as nitrofurantoin or fosfomycin 4, 3. However, if this represents complicated UTI, pyelonephritis, or bacteremia with urinary source, the parenteral carbapenem approach is justified 3.