The preservation surgery of the anal sphincter muscle has become the standard procedure in the treatment of rectal cancer and, thanks to advancements in surgical techniques, can now be performed for tumors located closer to the anus. This method allows patients to avoid a permanent artificial anus, maintaining continuity of the intestines and enabling bowel movements through the anus, making it a highly preferred procedure. Furthermore, advancements in various tumor treatments have led to improved long-term survival rates.

Preservation surgery of the anal sphincter muscle is commonly used in the treatment of rectal cancer, resulting in approximately 90% of patients experiencing changes in bowel habits after surgery. These changes include characteristic diarrhea, urgent bowel movements, frequent bowel movements, and fecal incontinence, collectively known as Anterior Resection Syndrome (ARS). Particularly in the case of low rectal cancer, it often manifests as Low Anterior Resection Syndrome (LARS). These symptoms are most severe immediately after surgery, generally persisting in a significant degree for 1-2 years, with some improvement over time. However, for many patients, LARS remains a lifelong challenge, significantly impacting their quality of life. Nighttime symptoms of LARS, in particular, have a profound effect on sleep quality, potentially leading to a decline in overall quality of life.

Currently, there is no definitive method to completely cure LARS, and the available approaches focus on empirical treatments or short-term symptom control using medications such as loperamide.

Loperamide directly affects the neuromuscular system of the intestine, reducing its motility. This prolongs the time food stays in the intestine, allowing sufficient absorption of moisture and electrolytes, consequently reducing symptoms of diarrhea. Loperamide is available in two forms: loperamide oxide and loperamide hydrochloride. While loperamide oxide products like Arestal® were prescribed by doctors until August 2017, the approval was revoked, leaving loperamide hydrochloride as the only form used domestically. It comes in a single product containing 2 mg of loperamide hydrochloride and a combination product with 0.25 mg of loperamide hydrochloride, a sterilizing agent in the intestine (e.g., acrylonitrile, berberine), and an antispasmodic.

Transanal irrigation (TAI) is a method where patients self-administer water into the rectum through an enema, physically cleansing the anus and rectum. This technique is often used for patients with chronic constipation or fecal incontinence. TAI has proven beneficial, particularly in improving symptoms for patients experiencing bowel dysfunction following sphincter-preserving surgery, especially for those who underwent low anterior resection.

However, there is currently no research on the utility and safety of TAI for LARS patients, specifically addressing whether it can improve the nighttime symptoms associated with LARS syndrome and enhance sleep quality. Therefore, this study aims to investigate the impact of TAI on the symptoms of LARS syndrome.

Inclusion Criteria:

• Adults aged 19 years and above.
• Patients who have undergone low or ultra-low anterior resection surgery for rectal cancer (within 15cm from the anal verge).
• Patients at least 24 months post-surgery without stoma.
• Patients evaluated with a major LARS score.
• Patients who comprehend and have the ability to participate in this clinical trial.

Exclusion Criteria:

• Patients with recurrent colorectal cancer.
• Patients with concomitant metastatic colorectal cancer.
• Patients requiring permanent colostomy.
• Patients who have undergone postoperative cancer radiation therapy.
• Patients with underlying conditions not controlled by internal medical treatment.
• Patients with inflammatory bowel disease (IBD).
• Patients with symptoms of constipation or diarrhea not controlled by medication.
• Patients with preoperative symptoms of fecal incontinence.
• Patients allergic to the investigational drug.
• Patients deemed unsuitable for clinical trial participation by the principal investigator and study personnel.