Should Macrobid (Nitrofurantoin) Be Continued for This UTI?
Yes, continue Macrobid (nitrofurantoin) for this patient with uncomplicated UTI and >100,000 CFU/mL, as it remains first-line therapy according to current European guidelines, provided the organism is susceptible and the patient has no contraindications. 1
Key Decision Points
Verify This is Uncomplicated UTI
The culture shows >100,000 CFU/mL, which confirms significant bacteriuria 2. Before continuing nitrofurantoin, confirm this patient:
- Is a non-pregnant woman without anatomic/functional urinary tract abnormalities 2
- Has no signs of upper tract involvement (fever >38°C, flank pain, costovertebral angle tenderness) 2
- Has adequate renal function (creatinine clearance >60 mL/min) 3
If any of these are present, this becomes a complicated UTI or pyelonephritis requiring different management. 2
Confirm Organism Susceptibility
The culture note mentions cefazolin MIC ≤16 predicts susceptibility to oral cephalosporins for E. coli, Klebsiella pneumoniae, and Proteus mirabilis [@question context@]. However:
- Nitrofurantoin susceptibility must be directly tested—you cannot extrapolate from cephalosporin susceptibility 4
- E. coli typically maintains high susceptibility to nitrofurantoin (>90% in most regions) 5, 4
- If the organism is Proteus mirabilis, stop nitrofurantoin immediately as Proteus species are intrinsically resistant 2
Appropriate Dosing and Duration
If continuing nitrofurantoin for uncomplicated cystitis:
- Dose: 100 mg twice daily (not four times daily) 1, 6
- Duration: 5 days 1
- The UK promotes 3-day courses, but evidence supporting this shorter duration over 5 days is limited 7
When to Switch from Nitrofurantoin
Switch Immediately If:
- Upper tract involvement (pyelonephritis): Nitrofurantoin achieves insufficient blood/tissue concentrations and should be avoided 2
- Proteus species isolated: Intrinsically resistant 2
- Creatinine clearance <60 mL/min: Risk of treatment failure and peripheral neuropathy increases significantly 3
- Organism reported resistant to nitrofurantoin on susceptibility testing 1
Alternative Agents Based on Susceptibility:
If nitrofurantoin is inappropriate, consider based on local resistance patterns:
- Fosfomycin trometamol 3g single dose (first-line alternative) 1
- Pivmecillinam 400mg three times daily for 3-5 days (if available) 1
- Cephalexin or other oral cephalosporins if cefazolin MIC ≤16 and local E. coli resistance <20% 1
- Trimethoprim-sulfamethoxazole 160/800mg twice daily for 3 days only if local resistance <20% 2, 1
Critical Safety Monitoring
Watch for Serious Adverse Effects:
Nitrofurantoin carries significant risks, particularly with prolonged use:
- Pulmonary toxicity: Acute reactions (fever, cough, dyspnea) typically occur within first week; chronic reactions develop after ≥6 months of continuous therapy 3
- Peripheral neuropathy: May be severe or irreversible, especially with renal impairment, diabetes, anemia, or vitamin B deficiency 3
- Hepatotoxicity: Rare but can be severe (hepatitis, hepatic necrosis) 3
For a 5-day course in uncomplicated UTI, these risks are minimal, but patients should be counseled to stop immediately if respiratory symptoms or numbness/tingling develop. 3
Common Pitfalls to Avoid
- Do not use nitrofurantoin for pyelonephritis or complicated UTI—it does not achieve adequate tissue/blood levels 2
- Do not prescribe for patients with reduced renal function—both efficacy decreases and toxicity risk increases 3
- Do not assume susceptibility based on cephalosporin testing—direct susceptibility testing is required 4
- Do not use for Proteus species—intrinsically resistant despite in vitro susceptibility testing sometimes showing otherwise 2
- Avoid in elderly patients with multiple comorbidities where peripheral neuropathy risk is elevated 3