What is the recommended treatment and dosage for a patient with a urinary tract infection (UTI) who is allergic to penicillin?

Treatment for UTI in Penicillin-Allergic Patients

For patients with uncomplicated UTI and penicillin allergy, prescribe nitrofurantoin 100 mg twice daily for 5 days as first-line therapy, or alternatively fosfomycin 3 grams as a single dose. 1, 2, 3

First-Line Options for Uncomplicated Lower UTI (Cystitis)

Nitrofurantoin (Preferred)

• Dose: 100 mg orally twice daily for 5 days 3
• Key advantage: Minimal gastrointestinal side effects and excellent safety profile in penicillin-allergic patients 1
• Administration: Take with food to minimize GI disturbances 1
• Critical limitation: Only appropriate for cystitis/lower UTI, NOT for pyelonephritis or complicated UTI 1

Fosfomycin (Excellent Alternative)

• Dose: 3 grams as a single oral dose 2, 3
• Key advantage: Single-dose therapy eliminates concerns about multi-day treatment adherence 1
• Critical limitation: Only appropriate for lower UTI/cystitis, NOT for pyelonephritis 1

Trimethoprim-Sulfamethoxazole (If Local Resistance <20%)

• Dose: 160/800 mg (one double-strength tablet) twice daily for 3 days for women, 7 days for men 4, 3
• Important caveat: Use only if local E. coli resistance rates are <20% and patient has not had recent antibiotic exposure 2, 5
• For UTI treatment: 10-14 days is FDA-approved dosing, though shorter 3-day courses are commonly used 4

Treatment for Uncomplicated Pyelonephritis (Upper UTI)

Oral Therapy (Outpatient)

Fluoroquinolones are the primary penicillin-free option:

• Ciprofloxacin: 500-750 mg twice daily for 7 days 6
• Levofloxacin: 750 mg once daily for 5 days 6
• Prerequisite: Only use if local fluoroquinolone resistance is <10% 6

Oral cephalosporins (second-line, but safe in most penicillin-allergic patients):

• Cefpodoxime: 200 mg twice daily for 10 days 6
• Ceftibuten: 400 mg once daily for 10 days 6
• Important note: Cephalosporins have <5% cross-reactivity with penicillin allergies; avoid only in patients with history of anaphylaxis to penicillin 6

Trimethoprim-sulfamethoxazole (if susceptible):

• Dose: 160/800 mg twice daily for 14 days 6

Parenteral Therapy (Hospitalized Patients)

For patients requiring IV therapy, penicillin-free options include:

• Ciprofloxacin: 400 mg IV twice daily 6
• Levofloxacin: 750 mg IV once daily 6
• Gentamicin: 5 mg/kg IV once daily 6
• Amikacin: 15 mg/kg IV once daily 6
• Cephalosporins (if no anaphylactic penicillin allergy):
  • Ceftriaxone: 1-2 g IV once daily 6
  • Cefotaxime: 2 g IV three times daily 6
  • Cefepime: 1-2 g IV twice daily 6

Treatment for Complicated UTI

For complicated UTI in penicillin-allergic patients, empiric therapy depends on severity and risk factors for multidrug-resistant organisms: 6

• Fluoroquinolones remain first-line if local resistance permits 6
• Aminoglycosides (gentamicin or amikacin) are safe alternatives 6, 2
• Cephalosporins can be used unless true anaphylactic penicillin allergy 6
• For ESBL-producing organisms: Nitrofurantoin and fosfomycin remain options for lower UTI; carbapenems (meropenem 1 g IV three times daily) for upper tract or severe infections 6, 2

Critical Clinical Pitfalls

• Never use nitrofurantoin or fosfomycin for pyelonephritis - they achieve inadequate tissue concentrations in kidney parenchyma 1, 2
• Cephalosporin cross-reactivity: Safe in >95% of penicillin-allergic patients; avoid only with documented anaphylaxis history 6
• Fluoroquinolone resistance: Verify local resistance patterns are <10% before empiric use 6
• Duration matters: Men require 7 days minimum for any uncomplicated UTI regimen (versus 3-5 days for women) due to higher risk of prostatic involvement 3
• Always obtain urine culture before treatment in men, recurrent infections, treatment failures, or suspected resistant organisms 3