Urinary Tract Infections (UTIs) and Recurrent UTIs

Prophylaxis

• Maintain fluid intake to about 1.5 L per day for patients with low baseline intake.

• Intravaginal oestrogen for postmenopausal women can reduce recurrences.

• Methenamine hippurate 1 g every 12 hours can be used as a non-antibiotic preventive option. Review every 6 months.

• Cranberry may help some nonpregnant women under 50. Evidence is insufficient in older adults or with voiding problems.

• Not recommended: ascorbic acid. Evidence for D-mannose is not convincing.

• Do not use antibiotic prophylaxis for asymptomatic bacteriuria.

Recurrent UTI Definition

• ≥2 symptomatic UTIs in 6 months or ≥3 in 12 months, with at least one culture-confirmed episode.

Management Strategies

Antibiotic prophylaxis options

• Continuous low-dose for 6 months with review:

  • Trimethoprim 150 mg at night

  • Cephalexin 250 mg at night

  • Nitrofurantoin 50 mg at night

• Post-coital prophylaxis (single dose within 2 hours of intercourse, max once daily):

  • Nitrofurantoin 50 mg

  • Trimethoprim 150 mg

  • Cephalexin 250 mg

• Self-initiated therapy at symptom onset is appropriate for selected nonpregnant women and reduces overall antibiotic use.

Investigations

• MSU for MCS during symptomatic episodes.

• Consider imaging or referral if relapse with the same organism pattern, recurrent pyelonephritis, stones, obstruction or haematuria.

• In men, consider urology review to assess for prostatic disease.

Treatment

Women

• First-line: Nitrofurantoin 100 mg QID for 5 days.

• Second-line: Fosfomycin 3 g stat.

• Third-line: Trimethoprim 300 mg nocte for 3 days.

• If the above cannot be used: Cephalexin 500 mg BD for 5 days.

Notes:

• Consider simple analgesia first in selected women under 65 with mild cystitis and no risk factors; review at 48 hours.

• Avoid urinary alkalinisers with nitrofurantoin.

• Reserve fluoroquinolones for specific indications or susceptibility-directed therapy.

Pregnancy

• Screen once at 12–16 weeks for asymptomatic bacteriuria; treat if positive and repeat culture 1–2 weeks after completion.

• Acute cystitis or confirmed ASB (empirical while awaiting culture):

  • Nitrofurantoin 100 mg QID for 5 days — avoid from 37 weeks and in G6PD deficiency

  • Cephalexin 500 mg BD for 5 days

  • Fosfomycin 3 g stat

  • If susceptible: Amoxicillin 500 mg TDS for 5 days or Amoxicillin-clavulanate 875/125 mg BD for 5 days

  • Trimethoprim 300 mg daily for 3 days may be considered in 2nd or 3rd trimester if suitable

• Recurrent UTI in pregnancy: consider post-coital nitrofurantoin 50 mg or cephalexin 250 mg once; or continuous prophylaxis with cephalexin 250 mg nocte or nitrofurantoin 50 mg nocte until 37 weeks.

Men

• Lower UTI (prostatitis unlikely):

  • Nitrofurantoin 100 mg QID for 7 days, or

  • Trimethoprim 300 mg daily for 7 days

• Alternative: Cephalexin 500 mg BD for 7 days

• Always consider acute bacterial prostatitis if fever, pelvic/perineal pain or obstructive symptoms. Do not use nitrofurantoin if prostatitis is possible.

Pyelonephritis

Non-Severe Cases suitable for outpatient oral therapy

• Clinically stable, able to maintain oral hydration and take oral therapy, no sepsis, not pregnant, reliable follow-up.

• Send urine for MCS before treatment; reassess at 48 hours. Fever may take 48–72 hours to settle.

Treatment

• Empirical oral options:

  • Amoxicillin-clavulanate 875/125 mg TDS for 10 days

  • Penicillin allergy: Ciprofloxacin 500 mg BD for 7 days

• Step-down to narrowest effective agent when susceptible:

  • Amoxicillin 1 g TDS for 10 days, or

  • Trimethoprim–sulfamethoxazole 160/800 mg BD for 7 days, or

  • Cephalexin 1 g QID for 10 days

• Do not use nitrofurantoin or fosfomycin for pyelonephritis.

• Consider a single IV dose (eg ceftriaxone) before oral step-down if indicated by clinical context or local protocol.

Children

Who needs IV rather than oral

• Use IV therapy for children 3 months or older with risk factors for serious illness, systemic symptoms, or inability to tolerate oral therapy. Otherwise use oral therapy. 

Empirical oral therapy for acute pyelonephritis (age ≥1 month)

• Amoxicillin-clavulanate for 10 days

  • 1 to <2 months: 15/3.75 mg/kg TDS

  • ≥2 months: 22.5/3.2 mg/kg up to 875/125 mg TDS

• Cephalexin 25 mg/kg up to 1 g QID for 10 days

  • If 6-hourly adherence is unlikely and age ≥12 months: 45 mg/kg up to 1.5 g 8-hourly for 10 days

• Penicillin hypersensitivity

  • Ciprofloxacin 12.5 mg/kg up to 500 mg BD for 7 days, or

  • If liquid required: Trimethoprim–sulfamethoxazole 4/20 mg/kg up to 160/800 mg BD for 7 days

• Modify to the narrowest agent once culture is available. 

Culture-directed oral options

• Amoxicillin 30 mg/kg up to 1 g TDS for a total of 10 days, or

• Trimethoprim–sulfamethoxazole 4/20 mg/kg up to 160/800 mg BD for a total of 7 days, or

• Cephalexin as above; if resistant to all except ciprofloxacin, use ciprofloxacin 12.5 mg/kg up to 500 mg BD for 7 days. 

Empirical IV therapy (age ≥3 months)

• Gentamicin 7 mg/kg IV initial dose, or Tobramycin 7 mg/kg IV initial dose

• If IV likely to continue ≥72 hours, or aminoglycoside unsuitable: Ceftriaxone 50 mg/kg IV daily, or Cefotaxime 50 mg/kg IV 8-hourly

• Switch to oral when clinically stable and able to tolerate oral therapy. 

Duration and imaging

• Total duration (IV + oral) 7–10 days. Seven days is reasonable if the whole course is IV beta-lactam, or if oral continuation is ciprofloxacin or trimethoprim–sulfamethoxazole; otherwise use 10 days.

• If not improving clinically within 48 hours of appropriate antibiotics, request a renal ultrasound. Do not request ultrasound for persistent fever alone.

• Do not perform post-treatment urine culture in asymptomatic children. 

Note: In adults, cephalexin is typically 500 mg BD for cystitis, and 1 g QID when used as step-down for pyelonephritis.