What is the recommended dose of ertapenem (a carbapenem antibiotic) for an 83-year-old female patient with a urinary tract infection (UTI) and normal renal function, with a creatinine level of 0.50, Blood Urea Nitrogen (BUN) of 20, and Glomerular Filtration Rate (GFR) of 93?

Ertapenem Dosing for UTI in an 83-Year-Old Female with Normal Renal Function

For an 83-year-old female with a urinary tract infection and normal renal function (creatinine 0.50, BUN 20, GFR 93), the recommended dose of ertapenem is 1 gram intravenously once daily.

Dosing Rationale

The patient's renal function parameters are within normal limits for her age:

• Creatinine: 0.50 mg/dL (normal)
• BUN: 20 mg/dL (normal)
• GFR: 93 mL/min/1.73m² (normal)

According to the FDA drug label for ertapenem 1, no dosage adjustment is necessary for elderly patients with normal (for their age) renal function. The standard dose of 1 gram IV once daily is appropriate in this case since:

1. The patient has a GFR >30 mL/min/1.73m²
2. Dose reduction is only indicated for patients with severe renal impairment (CrCl ≤30 mL/min/1.73m²)

Age-Related Considerations

While the European Association of Urology guidelines 2 note that geriatric patients (>70 years) often exhibit geriatric-typical multimorbidity and those >80 years are included in this group regardless of systemic diseases, the antimicrobial treatment of UTIs in older people generally aligns with treatment for other patient groups when renal function is preserved.

Key points to consider:

• Elderly patients may have altered pharmacokinetics of ertapenem
• The FDA label 1 indicates that total and unbound AUC increased 37% and 67%, respectively, in elderly adults relative to young adults
• These changes are attributed to age-related changes in creatinine clearance
• Despite these changes, no dosage adjustment is recommended when renal function is normal for age

Administration and Duration

• Administer 1 gram IV over 30 minutes once daily
• Treatment duration should follow standard guidelines for complicated UTIs, typically 7-14 days depending on clinical response
• Pharmacokinetic studies 3 have shown that ertapenem maintains high urine concentrations (>128 mg/L) for at least 40% of the dosing interval, which is effective for treating UTIs

Monitoring Recommendations

• Monitor for clinical improvement within 48-72 hours
• No routine post-treatment urinalysis or urine cultures are indicated if symptoms resolve 2
• If symptoms do not resolve by the end of treatment or recur within 2 weeks, obtain urine culture and antimicrobial susceptibility testing 2
• Monitor for potential adverse effects, including gastrointestinal symptoms, headache, and infusion site reactions

Important Considerations for Elderly Patients

• Assess for potential drug interactions, as elderly patients often take multiple medications
• Evaluate hydration status regularly, as elderly patients are more susceptible to dehydration
• Consider the presence of urinary catheters or anatomical abnormalities that may complicate treatment
• Be aware that elderly patients may present with atypical symptoms of UTI, including confusion, falls, or functional decline 2

Pitfalls to Avoid

1. Do not reduce the dose based on age alone when renal function is normal
2. Do not extend treatment unnecessarily beyond the recommended duration
3. Avoid assuming treatment failure too early; clinical response may take longer in elderly patients
4. Do not treat asymptomatic bacteriuria, which is common in the elderly and does not require antimicrobial therapy

Ertapenem is an appropriate choice for complicated UTIs, particularly those caused by extended-spectrum β-lactamase (ESBL)-producing organisms, with studies showing high clinical efficacy and safety in treating complicated UTIs 4, 5.