Uncomplicated Acute Pyelonephritis

Definition, Clinical Features, DiagnosisTop

Uncomplicated acute pyelonephritis results from an ascending infection that originates in the lower urinary tract. Infection and inflammation involve the pyelocalyceal system and the adjacent renal parenchyma. The clinical features may vary, ranging from symptoms of cystitis (subclinical acute pyelonephritis is frequently present) to urosepsis. In typical cases, signs and symptoms occurring within the first 24 hours include flank pain of varying intensity, malaise, fever, and rigors; dysuria, nausea, and vomiting may also be present. Physical examination reveals flank pain on percussion (Murphy kidney punch; usually unilateral) and in some patients also lower abdominal tenderness caused by the ongoing cystitis that preceded pyelonephritis.

In each case, samples for urinalysis and urine cultures should be obtained prior to starting treatment; in individuals admitted to the hospital, blood cultures should also be performed. Leukocyturia is almost always present and urine cultures are positive in 90% of patients (typically revealing bacteriuria ≥105 colony-forming units [CFU]/mL). Imaging studies should be considered if or when diagnosis is not conclusive, fever persists for >48 hours while on appropriate antibiotic treatment, the patient’s clinical condition deteriorates during treatment, or the patient has a recurrent episode of acute pyelonephritis.

TreatmentTop

Treatment should always be based on urine culture results and continued for 7 to a maximum of 14 days. Empiric treatment should be continued until urine culture results become available.

Because resistance rates of community-acquired Escherichia coli strains to fluoroquinolone are >10% in many areas in Canada, it can no longer be recommended as the first-line choice for empiric treatment.

1. Compliant patients in good clinical condition with mild symptoms may be treated on an outpatient basis with IV ceftriaxone 1 to 2 g followed by (if susceptible):

1) First-line agents: Trimethoprim/sulfamethoxazole 960 mg bid for 7 to 14 days or oral fluoroquinolones for 7 days (eg, ciprofloxacin 500 mg bid or levofloxacin 250 mg once daily).

2) Alternative oral agents (if the first-line drugs cannot be used) for 10 to 14 days: Cephalexin (INN cefalexin) 500 mg qid, cefpodoxime 200 mg bid, amoxicillin + clavulanic acid 1 g bid.

A single daily dose of an aminoglycoside can be used (eg, IV gentamicin 5-7 mg/kg) for empiric treatment in patients with contraindications to ceftriaxone. If resistance rates in community-acquired Escherichia coli strains are <10%, antibiotics listed above under 1) and 2) can be considered for empiric treatment before culture results are available.

2. Patients requiring hospitalization: Hospitalization is indicated in the case of dehydration, persistent nausea and vomiting, lack of improvement or worsening of symptoms in the course of outpatient treatment, inconclusive diagnosis, or pregnancy. Drugs are typically administered IV, starting with empiric treatment using one of the following antimicrobial agents:

1) IV ceftriaxone 1 to 2 g once daily.

2) Aminoglycosides: IV gentamicin 5 to 7 mg/kg once daily or 1 mg/kg every 8 hours as monotherapy or in combination with IV ampicillin 1 g every 6 hours.

3) Other alternatives include piperacillin/tazobactam 4.5 g every 8 hours as well as carbapenems in case of a high risk of multiresistant pathogens.

4) In the case of a pathogen susceptible to fluoroquinolones: Oral ciprofloxacin 500 mg bid or 200 to 400 mg IV every 12 hours if the patient is not a candidate for oral treatment.

Treatment should be modified according to the results of urine and blood cultures. If fever has resolved and clinical improvement is observed (usually within 72 hours), therapy with an oral antimicrobial agent selected on the basis of microbiology results should be started (the drug may be different from the IV agent).Evidence 1Strong recommendation (benefits clearly outweigh downsides; right action for all or almost all patients). Moderate Quality of Evidence (moderate confidence that we know true effects of the intervention). Quality of Evidence lowered due to indirectness, as although the switch from IV to oral treatment is supported by several randomized controlled trials and observational studies, most studies are not specific to UTI or have limited power to rule out inferiority. Monmaturapoj T, Montakantikul P, Mootsikapun P, Tragulpiankit P. A prospective, randomized, double dummy, placebo-controlled trial of oral cefditoren pivoxil 400mg once daily as switch therapy after intravenous ceftriaxone in the treatment of acute pyelonephritis. Int J Infect Dis. 2012 Dec;16(12):e843-9. doi: 10.1016/j.ijid.2012.07.009. Epub 2012 Aug 28. PMID: 22951426.