Acute pyelonephritis (APN) corresponds to infections of the renal parenchyma. The annual incidence of these infections is estimated at 4-6 million cases in France, with 60 to 90% of patients managed in general city medicine. The ceftriaxone, parenteral third-generation cephalosporin (C3G), occupies an important place in the antibiotic treatment of these infections: this is the recommended probabilistic treatment, and in some situations the treatment can be continued in its entirety via a Ceftriaxone monotherapy.

The aim of the last antibiotic plan is to avoid the use of antibiotic therapies with a high selection capacity (cephalosporins, penicillins, fluoroquinolones, etc.) and thus reduce the incidence and prolongation over time of the digestive carriage of multi-resistant bacteria .

To date, there have been few studies evaluating the impact of ceftriaxone on the emergence of multi-resistant bacteria on an individual scale, with rather heterogeneous results (13-86% C3G resistance).

Thus, before considering randomized studies comparing the ecological impact of different molecules or therapeutic regimens in the treatment of ANP, it is necessary to have a precise and rigorous evaluation of the ecological impact of the molecule reference in this indication.

The investigators propose a study to evaluate the impact on the digestive flora at 1 month of a ceftriaxone antibiotic therapy (7 days) in the management of acute pyelonephritis in women.

Inclusion Criteria:

• Female
• Over 18 years old
• Admitted to the emergency department with a diagnosis of PNA (simple or at risk of complications, without signs of seriousness)

Exclusion Criteria:

• Hypersensitivity to ceftriaxone, to another cephalosporin or to any of the excipients
• A history of severe hypersensitivity (eg anaphylactic reaction) to another class of antibacterial agent in the beta-lactam family (penicillins, monobatams and carbapenems)
• Severe pyelonephritis, including obstructive APN
• Pyelonephritis in patients with a urinary catheter
• Antibiotic treatment in the previous 6 months
• Chronic dialysis patient
• Patient with hepatic impairment
• Pregnancy or breast-feeding in progress