Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.
Obstructed infected kidney and urgent decompression
Essential points for quick revision.
2 min synopsisUK scopeSources checked 8 Sept 2026Clinical review pending
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Infection behind obstruction
A suspected infected obstructed kidney is a urological emergency, even before shock develops.
Action: Contact urology immediately, start appropriate systemic antibiotics and arrange urgent decompression with concurrent resuscitation.
Synopsis
Recognise an infected obstructed collecting system, organise urgent decompression and distinguish life-saving drainage from definitive treatment of the obstructing lesion.
Infection with an obstructed collecting system requires urgent drainage as well as antibiotics; stone size does not remove that emergency.
Contact urology immediately and coordinate imaging, cultures, antibiotics, resuscitation and a stent or nephrostomy decision.
When pyonephrosis is suspected with acute kidney injury, obtain urinary tract ultrasound immediately, within six hours of assessment; necessary drainage should occur as soon as possible.
Key red flags
Infection plus obstruction
Suspect the combination when fever or systemic illness accompanies renal colic, hydronephrosis, a known ureteric stone or another obstructing lesion. A relatively small stone can still obstruct a critical location.
Deteriorating physiology
Hypotension, tachypnoea, confusion, rising lactate or reduced perfusion signals escalating risk. Call senior and critical care help while the drainage pathway is being arranged, rather than completing a sequential series of referrals.
Investigation priorities
01
Urgent urinary tract imagingFirst step
Identify dilation and the likely site of impaired drainage.
Management branches
Worked caseDrain the infected collecting system
A fifty one year old woman has fever and an obstructing distal ureteric stone.
She has rigors, right flank pain, creatinine 156 from a baseline of 72 and lactate 2.7, with blood pressure 104/64. Imaging shows a six millimetre distal stone with hydronephrosis. Urology and the senior acute clinician are contacted immediately; cultures and resuscitation proceed together.
Microbiology selects ceftriaxone 2 g intravenously daily using a recent susceptible isolate and the current renal risk, while urgent retrograde stenting is arranged because access is straightforward and the team is immediately available. This is drainage, not ureteroscopic stone fragmentation; pus obtained above the stone is sent for culture.
Key medicines
Ceftriaxone 2 g intravenous infusionIn the microbiology-selected example, administer 2 g intravenously every twenty four hours over at least thirty minutes; review culture and intravenous need within forty eight hours.This example is not universal empirical cover for ESBL organisms or every post-instrumentation infection. Exclude hypersensitivity to ceftriaxone or any other cephalosporin, as well as severe hypersensitivity to a different beta lactam; check renal plus hepatic status. Avoid concurrent calcium-containing intravenous infusions and flush shared lines for sequential adult use; never use lidocaine diluent intravenously. Reassess if neurological changes, severe diarrhoea or a serious rash occurs.
Cefalexin 500 mg capsules after stabilisationFor the susceptible oral continuation shown, prescribe 500 mg orally three times daily, counting previous active intravenous days within the agreed ten day total course.Do not use an oral switch to compensate for persisting obstruction or shock. Do not prescribe after cefalexin, formulation or cephalosporin hypersensitivity. A severe penicillin-reaction history requires specialist antibiotic choice. Check renal dose adjustment and the culture susceptibility; a result from an earlier episode is not a guarantee of current activity. Record the intended stop date and reassess diarrhoea or rash promptly.
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 8 Sept 2026; clinical approval remains outstanding.