What is the appropriate dosing of meropenem (Merrem) for an Extended-Spectrum Beta-Lactamase (ESBL) urinary tract infection (UTI) in an 89-year-old patient with a history of ESBL resistance and potential Impaired renal function?

Meropenem Dosing for ESBL UTI in an 89-Year-Old Patient

For an 89-year-old patient with ESBL UTI and history of ESBL resistance, the recommended dose of meropenem is 1 gram IV every 8 hours, with dose adjustment based on renal function. 1

Dosing Considerations for Elderly Patients with ESBL UTI

Initial Dosing Based on Renal Function

• Normal renal function (CrCl >50 mL/min): 1 gram IV every 8 hours 1
• Moderate renal impairment (CrCl 26-50 mL/min): 1 gram IV every 12 hours 1
• Severe renal impairment (CrCl 10-25 mL/min): 500 mg (half dose) IV every 12 hours 1
• End-stage renal disease (CrCl <10 mL/min): 500 mg (half dose) IV every 24 hours 1

Administration Method

• Administer as intravenous infusion over 15-30 minutes 1
• Extended infusion (3-hour) should be considered for better pharmacodynamic profile, especially in patients with higher MICs 2

Rationale for Meropenem in ESBL UTI

Meropenem is the appropriate choice for ESBL UTI because:

1. It maintains high efficacy against ESBL-producing organisms with 95% susceptibility rates 3
2. It is specifically recommended for infections with ESBL-producing Enterobacteriaceae 4
3. For UTIs specifically, meropenem is indicated when there is a high suspicion of ESBL organisms 4

Special Considerations for Elderly Patients

• Elderly patients (>65 years) typically have reduced renal function, resulting in lower meropenem clearance, even without direct influence of age itself 5
• Safety profile of meropenem in elderly and/or renally impaired patients is excellent, with adverse event patterns similar to younger patients 6
• Renal function assessment is critical before initiating therapy, as it significantly impacts dosing intervals and amounts 1

Monitoring Recommendations

• Assess renal function at baseline and regularly during treatment
• Monitor for clinical response within 48-72 hours
• Consider extended infusion (3-hour) for better PK/PD profile in patients with higher MICs 2
• Watch for potential development of resistance, especially with history of previous meropenem use 3

Potential Pitfalls and Caveats

• Resistance development: 4.9% of ESBL E. coli have shown meropenem resistance in patients with prior meropenem exposure 3
• Renal function overestimation: Standard formulas may overestimate renal function in the elderly, potentially leading to overdosing
• Drug interactions: Consider concurrent medications that may affect renal function
• Duration of therapy: For complicated UTIs caused by ESBL organisms, treatment should continue for 7-14 days depending on clinical response

In summary, meropenem at 1 gram IV every 8 hours (with appropriate renal adjustment) is the optimal choice for this 89-year-old patient with ESBL UTI and history of resistance, but careful monitoring of renal function and clinical response is essential.