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urinary tract infections

in review 5 min read Updated 2026-08-23
infectious-diseases urology nephrology empiric-antibiotics
Contents
urinary tract infections

Uncomplicated cystitis: nitrofurantoin or TMP-SMX first-line (avoid fluoroquinolones). Pyelonephritis: severity determines setting — outpatient with fluoroquinolone or TMP-SMX if susceptible; inpatient with ceftriaxone. Complicated UTI (obstruction, catheter, male, structural): broader cover + imaging. Always distinguish infection from asymptomatic bacteriuria — do not treat ASB in non-pregnant adults.

uncomplicated cystitis empiric antibiotics
  • first-line: nitrofurantoin 100 mg PO BID × 5 days
  • alternative: TMP-SMX 160/800 mg (DS) PO BID × 3 days (if local resistance <20%)
  • if allergy/resistance to above: fosfomycin 3 g PO single dose (inferior cure rates)
  • avoid: fluoroquinolones for uncomplicated cystitis (save for pyelonephritis/complicated UTI)
  • no culture needed for classic uncomplicated cystitis in women — treat empirically
acute pyelonephritis empiric antibiotics
  • outpatient (mild, tolerating PO): ciprofloxacin 500 mg PO BID × 7 days or TMP-SMX DS PO BID × 14 days (if susceptible)
  • inpatient first-line: ceftriaxone 2 g IV daily
  • if penicillin/cephalosporin allergy: ciprofloxacin 400 mg IV q12h (or levofloxacin 750 mg IV daily)
  • if septic / prior resistant organisms: piperacillin-tazobactam 4.5 g IV q6h or meropenem 1 g IV q8h
  • step down to PO when afebrile ≥48 h + improving — complete total 7–14 days based on agent and response
  • ALWAYS obtain urine culture before antibiotics for pyelonephritis — tailor therapy to susceptibilities
local antibiogram

E. coli resistance to TMP-SMX exceeds 20% in many Canadian centres — check local rates before empiric use. Fluoroquinolone resistance is rising nationally.

classification

typedefinitionexamples
uncomplicated cystitislower UTI in a non-pregnant woman with normal urinary tractdysuria, frequency, urgency
uncomplicated pyelonephritisupper UTI in a non-pregnant woman with normal urinary tractfever, flank pain, CVA tenderness
complicated UTIUTI with factors increasing treatment failure riskobstruction, catheter, male sex, pregnancy, transplant, structural abnormality, immunocompromised

when to culture

  • not needed: classic uncomplicated cystitis in women — treat empirically
  • always culture: pyelonephritis, complicated UTI, male UTI, treatment failure, recurrent UTI (≥3/year), recent antibiotics, catheter-associated, pregnancy

empiric therapy — detail

uncomplicated cystitis

agentdosedurationnotes
nitrofurantoin monohydrate100 mg PO BID5 daysfirst-line; avoid if CrCl <30 mL/min or suspected pyelonephritis
TMP-SMXDS (160/800) PO BID3 daysfirst-line if local resistance <20%; avoid in late pregnancy
fosfomycin3 g PO single dose1 doseinferior efficacy; reserve for resistant organisms
pivmecillinam400 mg PO BID3–5 daysavailable in Canada; reasonable alternative

acute pyelonephritis

Outpatient (mild, no vomiting, reliable follow-up):

  • ciprofloxacin 500 mg PO BID × 7 days — Sandberg (2012): 7 days non-inferior to 14 days
  • or TMP-SMX DS PO BID × 14 days (if susceptible — longer course needed vs fluoroquinolone)
  • give a single dose of ceftriaxone 1–2 g IV/IM before discharge if using TMP-SMX empirically (covers while awaiting susceptibilities)

Inpatient:

  • ceftriaxone 2 g IV daily (most common Canadian choice)
  • if septic or ESBL risk: piperacillin-tazobactam 4.5 g IV q6h or ertapenem 1 g IV daily or meropenem 1 g IV q8h
  • step down to PO guided by susceptibilities when afebrile ≥48 h

complicated UTI / catheter-associated

  • remove or change catheter if possible — single most effective intervention
  • ceftriaxone 2 g IV daily or ciprofloxacin 400 mg IV q12h
  • if ESBL/resistant organism history: piperacillin-tazobactam or meropenem
  • treat 7–14 days; shorter courses (5–7 days) may suffice for rapid responders per IDSA 2024

penicillin allergy pathway

allergy historyapproach
non-immune side effectscephalosporins safe — use ceftriaxone
distant mild rashceftriaxone (<2% cross-reactivity)
confirmed anaphylaxisciprofloxacin 400 mg IV q12h or levofloxacin 750 mg IV daily
severe allergy + ESBLmeropenem safe (carbapenem cross-reactivity with penicillin is negligible); if anaphylaxis to all β-lactams → aminoglycoside + ID consult

duration

scenarioduration
uncomplicated cystitis (nitrofurantoin)5 days
uncomplicated cystitis (TMP-SMX)3 days
outpatient pyelonephritis (fluoroquinolone)7 days
outpatient pyelonephritis (TMP-SMX)14 days
inpatient pyelonephritis7–14 days total (IV → PO)
complicated UTI / CAUTI7–14 days
male UTI7–14 days (lower risk of recurrence with 14 days)

asymptomatic bacteriuria

do not treat asymptomatic bacteriuria

Positive urine culture without urinary symptoms does not require antibiotics in non-pregnant adults — including elderly, catheterised, and diabetic patients. Treatment does not reduce mortality or symptomatic episodes and drives resistance.

Exceptions — screen and treat ASB in:

  • pregnancy (screen each trimester)
  • pre-urological procedures with mucosal breach

Pyuria does not distinguish ASB from UTI — pyuria alone is never an indication for antibiotics.

traps

  • cloudy/malodorous urine is not a UTI — do not culture or treat without urinary symptoms
  • altered mental status in the elderly is rarely caused by UTI without other localising symptoms — search for other causes before attributing to a positive urine culture
  • nitrofurantoin does not achieve adequate renal/tissue levels → ineffective for pyelonephritis
  • fosfomycin is a single-dose convenience agent but has lower cure rates — do not use for pyelonephritis
  • in men, always consider prostatitis (longer treatment, fluoroquinolone or TMP-SMX × 4–6 weeks) — recurrent “UTI” in a man warrants urology referral
  • catheter-associated: 48 h of catheterisation → virtually 100% colonisation; only treat if systemic symptoms

Key references

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