The surgical site infection is one of the most important causes of postoperative morbidity. The appropriate antibiotic prophylaxis is one of the most effective ways to prevent surgical site infections. The recommendations of the French Society of Anesthesia Resuscitation on antibiotic prophylaxis in long surgeries are based on low documentation, including frequency and dosage of reinjection.

The main objective of the study is to describe the tissue and plasma pharmacokinetics of cefoxitin after repeated injections.

This is an open monocentric study (phase 4) including adults aged 18 to 80 years in need of major abdominal surgery whose foreseeable time exceeds 4 hours and justifying an antibiotic prophylaxis by cefoxitin.

They receive 2 g cefoxitin parenterally at least 30 minutes before the incision and then every 2 hours until closing.

The primary endpoints are:

• Total and plasma free concentrations of cefoxitin 0, 10, 30, 60, 90, 120 minutes after start of each infusion cefoxitin
• Tissue free concentrations of cefoxitin every 20 minutes after the start of the first infusion cefoxitin until skin closure
• Urinary concentrations of cefoxitin

Inclusion Criteria:

• Patients who underwent major abdominal surgery whose forseeable time exceeds 4 hours and requires an antibiotic prophylaxis by cefoxitin

Exclusion Criteria:

• morbid obesity (BMI > 35 kg/m²)
• severe renal impairment (clearance creatinine < 30ml/min)
• beta lactam hypersensitivity
• pregnancy