Acetaminophen (Tylenol) is a commonly used medication after surgery to control pain. Tablets for oral use and suppositories for rectal use are the most frequently employed forms of acetaminophen after surgery. Intravenous (IV) acetaminophen is widely used in several countries but is not a standard medication for the adult population in Canada. It is mainly considered when it is impossible to take medication in tablet or suppository form. Opioids (Morphine, Hydromorphone, Oxycodone, etc.) are another class of medications commonly used after surgery for pain management. While they are generally very effective and stronger than acetaminophen or other pain relievers (e.g., ibuprofen/Advil), reducing their use is preferable, as they can cause various side effects such as nausea, dizziness, and dependence. IV acetaminophen may help control pain while also reducing opioid consumption. However, there are few high-quality scientific studies proving the benefits of IV acetaminophen compared to other forms, such as tablets or suppositories. Acetaminophen has been available in Canada for many years and has already been recommended for use in Quebec by the Institut national d'excellence en santé et services sociaux (INESSS) under certain conditions. This study aims to validate its benefits with clear data.

In 2019, the Institut national d'excellence en santé et services sociaux (INESSS) stated that IV acetaminophen is an acceptable short-term pain treatment option in combination with opioid analgesics for adults and children aged two years and older when oral (PO) and rectal (IR) acetaminophen cannot be used. Despite this recommendation, there is limited data on IV acetaminophen in patients with a compromised enteral route, even though this is likely one of the populations that could benefit the most from such an intervention. Patients undergoing abdominal surgeries are a prominent example of individuals with a compromised enteral route. Some data exist for other types of surgeries, such as orthopedic surgery. However, such data is challenging to extrapolate to abdominal surgeries since orthopedic surgery does not affect the digestive system. Furthermore, several studies use comparators that do not accurately reflect clinical practice, such as placebo. This study will therefore use standard treatment as a comparator, allowing for a better assessment of IV acetaminophen's role in the therapeutic arsenal.

IV acetaminophen is approved and marketed in Canada. It is not an investigational product. Furthermore, it is currently used in other hospital centers and has already been used at the Centre hospitalier de l'Université de Montréal (CHUM). Given current budgetary limitations, PO and IR formulations of acetaminophen have been preferred over the IV formulation, as their economic burden is less than IV acetaminophen.

Currently, pharmacists play a central role in the healthcare system as medication experts and key players in patient care in both community and hospital settings. Over the years, pharmacists in Québec have also become prescribers by law. They are valuable allies in hospitals, ensuring proper treatment follow-up and continuously validating that pharmacological care standards for patients of the CHUM are met.

The research question is as follows: Compared to standard local postoperative treatment, does IV acetaminophen reduce the amount of opioids administered within the first 72 postoperative hours in patients with a compromised enteral route in the abdominal surgery units of a Québec university hospital center?

Inclusion Criteria:

• Age 18 years or older.
• Underwent abdominal surgery
• Underwent elective surgery.
• Hospitalized in the digestive surgery, hepatobiliary and pancreatic surgery, or gynecology and gynecologic oncology units at CHUM.
• Declared NPO immediately post-surgery, meaning they cannot take oral medications.

Exclusion Criteria:

• Hypersensitivity to acetaminophen or an excipient in the administered formulations
• Hepatic insufficiency with a Child-Turcotte-Pugh score of B or C.
• Weight < 50 kg (patients requiring a lower acetaminophen dose).
• Active pregnancy or breastfeeding.
• Opioid use disorder (OUD) under active treatment
• Non-opioid-naïve patients: those who received a long-acting opioid within seven days preceding surgery. This criterion will be verified through patient interviews and cross-checked with medical records.
• Use of illicit recreational substances.
• Prior participation in this study.
• Ectopic patients: physically located in a unit other than digestive surgery (11 South), hepatobiliary and pancreatic surgery (14 South), or gynecology and gynecologic oncology (12 South).