Synopsis
Recognise renal parenchymal infection and urinary sepsis, obtain cultures, select tissue-active treatment and secure urgent drainage when obstruction makes antibiotics insufficient.
- Pyelonephritis causes fever, flank or loin pain, systemic upset and urinary symptoms, although lower urinary symptoms may be absent.
- Send a midstream urine culture before antibiotics in every suspected acute pyelonephritis case when this does not delay treatment.
- Assess for sepsis and obstruction at presentation; an infected blocked system needs drainage as well as antimicrobial therapy.
- Eligible stable non-pregnant adults may receive an oral regimen; vomiting, severe illness, pregnancy or high complication risk supports hospital referral.
- NICE oral options include cefalexin 500 mg twice or three times daily for seven to ten days, adjusted within guidance for severe infection.
- Use co-amoxiclav or trimethoprim only when culture confirms susceptibility; reserve ciprofloxacin for when other recommended agents are inappropriate.
- Intravenous options are selected from local policy, prior microbiology and renal function; ceftriaxone 1 to 2 g once daily is one NICE-listed option.
- Review intravenous therapy by 48 hours and step down to the narrowest effective oral agent when physiology, intake and susceptibility permit.
Key red flags
Hypotension, tachypnoea, confusion, mottling, rising lactate or oliguria indicates urinary sepsis.
Flank pain with anuria, hydronephrosis, stone history or solitary kidney suggests obstructed infection.
Pregnancy with fever or flank pain requires urgent obstetric-aware assessment and usually hospital care.
Persistent vomiting, severe dehydration or inability to take oral treatment requires intravenous therapy and reassessment.
Failure to improve within 48 hours raises concern for resistance, abscess, obstruction or an alternative diagnosis.
Fever, rigors, loin or flank pain, costovertebral-angle tenderness, nausea and vomiting support pyelonephritis, with or without dysuria and frequency.
Altered consciousness, low blood pressure, tachypnoea, hypoxaemia, oliguria, mottling or raised lactate indicates sepsis requiring immediate escalation.
Colicky pain, haematuria, anuria, known stones, hydronephrosis, pelvic malignancy, neurogenic bladder or solitary kidney increases urgency for imaging and drainage.
Persistent fever, focal tenderness or bacteraemia despite active therapy suggests an abscess, infected cyst or other undrained focus.
Pregnancy, diabetes, transplantation, immune suppression, male sex, renal impairment and recent instrumentation lower the threshold for admission and imaging.
Investigation priorities
Confirm the urinary organism and allow directed antimicrobial treatment.
Management branches
Pyelonephritis is accompanied by organ dysfunction, shock, severe vomiting or inability to take oral treatment.
- Use ABCDE, measure glucose and lactate, establish access, monitor urine output and give oxygen and intravenous crystalloid according to physiology.
- Obtain urine and blood cultures promptly and start a locally recommended intravenous regimen adjusted for allergy, renal function and previous resistant isolates.
- Image urgently when obstruction, abscess, emphysematous infection or another source is possible and involve urology before deterioration.
- Review antimicrobial route within 48 hours, but continue inpatient monitoring until sepsis and oral intake are reliably improving.
A non-pregnant adult is stable, can take fluids and medicine and has no immediate complication concern.
- Obtain urine culture and assess pregnancy possibility, renal function, allergy, recent antibiotics and previous isolates before treatment.
- Choose a NICE-listed oral regimen using susceptibility and resistance risk; cefalexin is an option, while co-amoxiclav and trimethoprim require susceptibility.
- Use ciprofloxacin only when other commonly recommended antibiotics are inappropriate and explain serious fluoroquinolone adverse effects.