What antibiotic should I prescribe for an elderly male patient with a Foley catheter, taking citalopram (Selective Serotonin Reuptake Inhibitor), and a urine culture positive for Enterococcus faecalis/faecium and Staphylococcus aureus?

Treatment Recommendation for Polymicrobial UTI in Elderly Male with Foley Catheter

For this elderly male with a Foley catheter and polymicrobial urine culture growing Enterococcus faecalis/faecium and Staphylococcus aureus, you should prescribe vancomycin 1g IV every 12 hours (adjusted for renal function) for 14 days, as this provides coverage for both organisms and is the guideline-recommended agent for complicated UTI in catheterized patients with Gram-positive pathogens. 1, 2

Critical Initial Assessment

Before prescribing antibiotics, confirm this is true infection rather than colonization by verifying the patient has:

• Recent-onset dysuria PLUS at least one of: urinary frequency, urgency, new incontinence, costoverteboral angle tenderness, OR systemic signs (fever >100°F, rigors, hypotension, altered mental status) 3, 4, 2
• Catheterized patients have virtually universal bacteriuria and pyuria—only treat if systemic signs are present 4

Why Vancomycin is the Optimal Choice

Vancomycin provides comprehensive coverage for both pathogens in this polymicrobial infection:

• Enterococcus faecalis and faecium are uniformly susceptible to vancomycin (100% sensitivity) 1, 5
• Staphylococcus aureus (including MRSA) is covered by vancomycin 1, 6
• The European Society of Cardiology guidelines recommend vancomycin 30 mg/kg/day IV in 2 doses for enterococcal infections when beta-lactams cannot be used 1
• UTI in elderly males is always considered complicated and requires 14 days of therapy (not 7 days) to exclude occult prostatitis 2

Dosing and Monitoring Considerations

Vancomycin dosing:

• Standard dose: 1g IV every 12 hours 1
• Target serum trough levels (Cmin) ≥20 mg/L 1
• Adjust dose for renal dysfunction—elderly patients require less frequent dosing due to age-related decline in renal function 1, 4
• Monitor serum vancomycin concentrations weekly (twice weekly if renal impairment present) 1

Essential monitoring:

• Renal function assessment before initiating therapy and recheck in 48-72 hours 4
• Calculate creatinine clearance using Cockcroft-Gault equation to guide dosing 4
• Monitor for nephrotoxicity, especially given the patient's age 1

Critical Drug Interaction Warning

Citalopram interaction with vancomycin:

• Vancomycin can increase INR/prolong prothrombin time 7
• While citalopram itself doesn't directly interact with vancomycin, monitor for QT prolongation if the patient develops electrolyte abnormalities (hypomagnesemia) from vancomycin 7
• Check baseline electrolytes and monitor weekly 7

Alternative Regimens if Vancomycin Cannot Be Used

If vancomycin is contraindicated or the patient has renal impairment precluding its use:

• Daptomycin 6-10 mg/kg IV once daily is an alternative for both Enterococcus and S. aureus 1, 8
• Monitor CPK levels weekly due to risk of myopathy/rhabdomyolysis 7
• Linezolid 600 mg IV/PO every 12 hours for ≥8 weeks is another option, but monitor for hematological toxicity 1

For oral step-down therapy after clinical improvement (if susceptibilities allow):

• Nitrofurantoin 100 mg PO twice daily if E. faecalis is susceptible (avoid if CrCl <30-60 mL/min) 1, 4, 5
• Fosfomycin 3g single dose may be considered for E. faecalis UTI, though data are limited for complicated infections 1, 3

Common Pitfalls to Avoid

Do not use these agents:

• Fluoroquinolones (ciprofloxacin) have poor activity against enterococci and should be avoided unless all other options are exhausted 3, 4, 9
• Cephalosporins have no activity against enterococci due to intrinsic resistance 1, 9
• Trimethoprim-sulfamethoxazole is not reliably active against S. aureus or enterococci in this setting 9
• Ampicillin alone is inadequate for polymicrobial infection despite potential activity against ampicillin-susceptible enterococci 1

Critical catheter management:

• Remove or change the Foley catheter before obtaining culture specimens and initiating therapy 4, 8
• Consider catheter removal entirely if medically feasible, as indwelling catheters are associated with higher mortality in bacteremic UTI 6

When to Reassess

• Evaluate clinical response within 48-72 hours of initiating therapy 2
• Adjust antibiotics based on final culture susceptibilities 2, 8
• If no improvement by 72 hours, consider imaging to exclude abscess or obstruction 2
• Obtain blood cultures if systemic signs are present, as bacteremic UTI has 16% mortality in elderly patients 6