Intestinal Microbiome Modulation With Antibiotics in the Neoadjuvant Treatment of Locally Advanced Rectal Cancer

This intervention involves administering the oral antibiotic metronidazole during the first seven days of radiotherapy for patients with locally advanced rectal adenocarcinoma who are undergoing total neoadjuvant treatment. Metronidazole is considered a safe medication, with a very low risk of adverse effects. It is commonly used to treat infections caused by anaerobic bacteria that are part of the intestinal microbiota. Additionally, it is well established that certain genera of anaerobic bacteria are linked to a poorer response to treatment.