Treatment of Staphylococcal Urinary Tract Infection with Dicloxacillin
Dicloxacillin is NOT an appropriate first-line agent for staphylococcal UTI; treatment should be guided by culture and susceptibility testing, with empiric therapy based on local resistance patterns using agents that achieve adequate urinary and serum concentrations. 1
Critical First Step: Distinguish Pathogen from Contaminant
- Coagulase-negative staphylococci (including S. epidermidis) are typically contaminants and should not be treated in otherwise healthy patients 1
- S. saprophyticus is the exception—it is a true uropathogen, particularly in young women, and ranks second only to E. coli as a cause of acute UTI 2
- Culture confirmation is mandatory before initiating therapy to document true infection versus colonization 1
Why Dicloxacillin is Problematic for UTI
Dicloxacillin should not be used for febrile or complicated staphylococcal UTI because it does not achieve adequate serum concentrations to treat pyelonephritis or bacteremia. 3
- Agents that are excreted in urine but lack therapeutic bloodstream concentrations (like nitrofurantoin, and by extension dicloxacillin) are insufficient for upper tract infections 3
- While one case report from 1983 described dissolution of renal calculi with dicloxacillin in S. epidermidis infection 4, this represents an isolated observation and does not constitute evidence for routine use
- S. epidermidis is typically a contaminant rather than a pathogen 1, making the clinical significance of that case report questionable
Appropriate Empiric Treatment Approach
For Uncomplicated Staphylococcal Cystitis (S. saprophyticus)
- First-line empiric options based on local susceptibility patterns: 1
- S. saprophyticus is usually susceptible to standard UTI antibiotics except nalidixic acid 2
- Duration: 7 days for prompt symptom resolution 1
For Complicated or Catheter-Associated Staphylococcal UTI
- Replace indwelling catheters that have been in place ≥2 weeks before initiating therapy and obtain culture from the fresh catheter 1, 3
- Empiric combination therapy for systemic symptoms: 1
- Amoxicillin plus aminoglycoside, OR
- Second-generation cephalosporin plus aminoglycoside
- Duration: 7-14 days (7 days for prompt response, 10-14 days for delayed response or when prostatitis cannot be excluded) 1, 3
For Methicillin-Resistant Staphylococcus aureus (MRSA) UTI
If MRSA is documented (rare in UTI but possible):
- Vancomycin (intravenous) 3
- TMP-SMX (oral option if susceptible) 3
- Linezolid 600 mg PO/IV twice daily 3
Treatment Duration Algorithm
- 7 days: Uncomplicated UTI with prompt symptom resolution 1, 3
- 10-14 days: Delayed clinical response, complicated UTI, or when prostatitis cannot be excluded in men 1, 3
- Extend treatment and perform urologic evaluation if no defervescence by 72 hours 3
Critical Pitfalls to Avoid
- Do NOT treat asymptomatic bacteriuria (except in pregnant women or patients undergoing invasive urinary procedures)—this fosters resistance and increases recurrent UTI risk 1
- Do NOT use agents that lack adequate serum concentrations for febrile UTI (nitrofurantoin, and by extension dicloxacillin) 3
- Do NOT rely on chemical screening methods alone for S. saprophyticus—they may miss infection even when colony counts are <10^5 CFU/mL 2
- Do NOT continue empiric therapy without adjusting based on culture results—tailor antibiotics according to susceptibility testing once available 1
Special Considerations
Pediatric Patients (2-24 months)
- Oral and parenteral routes are equally efficacious 1
- Parenteral options: ceftriaxone 75 mg/kg every 24 hours, cefotaxime 150 mg/kg/day divided every 6-8 hours 3
- Oral options: amoxicillin-clavulanate 20-40 mg/kg/day in 3 doses, cephalexin 50-100 mg/kg/day in 4 doses 3