What is the appropriate antibiotic for a patient with a urinary tract infection?

Appropriate Antibiotic Selection for Urinary Tract Infection

Direct Answer

For uncomplicated cystitis in women, prescribe nitrofurantoin 100 mg twice daily for 5 days, fosfomycin 3 g as a single dose, or trimethoprim-sulfamethoxazole 160/800 mg twice daily for 3 days as first-line therapy. 1

Treatment by UTI Type and Patient Population

Uncomplicated Cystitis in Women

First-line options include:

• Nitrofurantoin monohydrate/macrocrystals: 100 mg twice daily for 5 days 1, 2
• Fosfomycin trometamol: 3 g single dose (recommended only for women with uncomplicated cystitis) 1
• Trimethoprim-sulfamethoxazole: 160/800 mg twice daily for 3 days 1

Alternative options when first-line agents cannot be used:

• Cephalosporins (e.g., cefadroxil): 500 mg twice daily for 3 days, only if local E. coli resistance is <20% 1
• Trimethoprim alone: 200 mg twice daily for 5 days (avoid in first trimester of pregnancy) 1

Critical caveat: Amoxicillin alone is no longer recommended due to global resistance rates showing a median of 75% of E. coli urinary isolates resistant to amoxicillin 1. Fluoroquinolones should be reserved for more serious infections due to serious safety concerns including tendon, muscle, joint, nerve, and central nervous system effects 1.

Uncomplicated Cystitis in Men

Men require longer treatment duration (7 days) compared to women: 1, 2

• Trimethoprim-sulfamethoxazole: 160/800 mg twice daily for 7 days 1, 3
• Trimethoprim: 7-day course 2
• Nitrofurantoin: 7-day course 2

Important consideration: Always obtain urine culture with susceptibility testing in men, as fluoroquinolones may also be prescribed based on local susceptibility patterns 1. Consider urethritis and prostatitis as alternative diagnoses 2.

Uncomplicated Pyelonephritis (Outpatient Treatment)

For mild to moderate pyelonephritis not requiring hospitalization:

• Ciprofloxacin: 500-750 mg twice daily for 7 days (oral) or 400 mg twice daily (IV) 1, 4
• Levofloxacin: 750 mg once daily for 5 days 1
• Trimethoprim-sulfamethoxazole: 160/800 mg twice daily for 14 days (only if susceptibility confirmed) 1

Alternative oral options (with initial IV dose recommended):

• Cefpodoxime: 200 mg twice daily for 10 days 1
• Ceftibuten: 400 mg once daily for 10 days 1

Critical requirement: Fluoroquinolone resistance should be <10% in your local area for empiric use 1. Recent meta-analyses confirm that 5-day fluoroquinolone courses are noninferior to 10-day courses, with clinical cure rates exceeding 93% 1.

Severe Pyelonephritis (Requiring Hospitalization)

Initial parenteral therapy options: 1

• Ceftriaxone: 1-2 g once daily 1
• Cefotaxime: 2 g three times daily 1
• Ciprofloxacin: 400 mg twice daily IV 1
• Levofloxacin: 750 mg once daily IV 1
• Amikacin: 15 mg/kg once daily (preferred over gentamicin for better resistance profile) 1

Reserve broad-spectrum agents (carbapenems, ceftolozane/tazobactam, ceftazidime/avibactam) only for early culture results indicating multidrug-resistant organisms 1.

Complicated UTI

Key principle: Complicated UTIs require individualized management based on underlying factors (obstruction, foreign body, immunosuppression, healthcare-associated infection, multidrug-resistant organisms) 1. The microbial spectrum is broader than uncomplicated UTI, including E. coli, Proteus, Klebsiella, Pseudomonas, Serratia, and Enterococcus species 1.

Essential step: Always obtain urine culture with susceptibility testing before initiating therapy 1. Address the underlying urological abnormality or complicating factor as this is mandatory for successful treatment 1.

Special Populations

Women with diabetes and no voiding abnormalities: Treat similarly to women without diabetes for acute cystitis 5.

Adults ≥65 years (nonfrail, no relevant comorbidities): Use same first-line antibiotics and durations as younger adults, but always obtain urine culture with susceptibility testing to adjust therapy after initial empiric treatment 2.

Pregnant women: Always obtain urine culture 1. Avoid trimethoprim in first trimester and trimethoprim-sulfamethoxazole in last trimester 1.

Diagnostic Considerations

For uncomplicated cystitis in women: Diagnosis can be made without office visit or urine culture when typical symptoms are present (frequency, urgency, dysuria, nocturia, suprapubic pain) without vaginal discharge 2, 5. A dipstick analysis showing pyuria, hematuria, or bacteriuria combined with clinical symptoms is sufficient 6.

Urine culture is recommended for: 1

• Suspected acute pyelonephritis
• Symptoms not resolving or recurring within 4 weeks after treatment completion
• Atypical symptoms
• Pregnant women
• All men with UTI symptoms
• Treatment failure or history of resistant isolates

Common Pitfalls to Avoid

Do not use β-lactam agents (amoxicillin-clavulanate, cefpodoxime-proxetil) as empirical first-line therapy for uncomplicated cystitis—they are less effective than other options 5.

Do not routinely prescribe fluoroquinolones for uncomplicated cystitis—reserve them for pyelonephritis and complicated infections due to serious adverse effects and the need to preserve their efficacy 1, 5.

Do not perform routine post-treatment urinalysis or cultures in asymptomatic patients 1.

For treatment failures: Assume the organism is not susceptible to the originally used agent and retreat with a 7-day regimen using a different antibiotic class 1.