Acute Pyelonephritis
NICE guideline [NG111] Pyelonephritis (acute): antimicrobial prescribing. Published: Oct 2018.
NICE CKS Pyelonephritis – acute. Last revised: Dec 2024.
Background Information
Definition
Acute pyelonephritis is defined as an infection of the kidney, it is a type of upper UTI.
See the Urinary Tract Infection (UTI) in Adults article for information on lower UTis.
Aetiology
Most common: E. coli (same as a lower UTI)
Some other causes:
- Klebsiella species (10%)
- Proteus mirablis (5%)
- Pseudomonas species
- Enterobacter species
Complications
- Sepsis and septic shock (major cause of morbidity and mortality)
- Renal / perinephric abscess
- Renal scarring and subsequent CKD
- Emphysematous pyelonephritis (a severe, necrotising infection characterised by gas formation within the renal parenchyma, most commonly seen in diabetics)
Diagnosis
Acute pyelonephritis can be diagnosed in the presence of:
- Typical clinical features of pyelonephritis, and
- Urine culture confirming bacteriuria
Imaging is not routinely required for diagnosis, but may be considered in atypical cases or when complications are suspected
Clinical Features
Typical features of acute pyelonephritis:
- Flank pain
- Renal angle tenderness (indicated by renal punch)
- Nausea / vomiting
- Fever (≥37.9°C)
Typical lower UTI features may or may not be present
Investigation and Diagnosis
Standard workup:
- Urine culture (mid-stream urine)
- Urine dipstick (commonly performed but NOT necessary for diagnosis)
Choice of imaging: CT abdomen and pelvis with contrast
- NB that imaging is NOT routinely required for diagnosis, it is reserved for atypical cases or when complications are suspected
- Typical findings in uncomplicated pyelonephritis
- Focal / multifocal areas of reduced renal parenchymal enhancement (typically wedge shape)
- Perinephric fat stranding
- Thickening of the renal fascia
- CT can detect the following complications
- Renal / perinephric abscess
- Emphysematous changes
- Hydronephrosis
Management
Antibiotic Therapy
ALL patients should be treated with antibiotics
- Obtain a urine sample BEFORE giving antibiotics
- Offer oral antibiotics if possible, unless the person cannot tolerate oral intake or very severe disease
Choice of antibiotics:
| 1st line oral antibiotics | Initial empirical therapy: cefalexin
If culture results are available and susceptible:
|
| 1st line IV antibiotics | Options:
Co-amoxiclav should only be given in combination or if culture results are available and susceptible Last resort: ciprofloxacin |
In addition to antibiotics, advise the person to drink enough fluids to avoid dehydration and offer analgesia (paracetamol +/- codeine)
The MHRA statement on fluoroquinolones (updated in Jan 2024) emphasises that fluoroquinolone antibiotics must only be prescribed when other commonly recommended antibiotics are inappropriate.
This restriction follows concerns over serious, disabling, long-lasting, and potentially irreversible side effects, including:
- MSK: tendonitis, tendon rupture (Achilles tendon rupture is classic), muscle pain and weakness, joint pain
- Neuro: peripheral neuropathy, altered taste / smell / hearing
- Mental health: depression, anxiety, panic attacks, memory impairment
- Psych: confusion, suicidal thoughts / attempts
A notable exception is acute bacterial prostatitis, where fluoroquinolones (ciprofloxacin / ofloxacin) remain the 1st line antibiotics despite the safety issues.