This is a clinical investigation to determine the efficacy of rectal versus intravenous acetaminophen in patients undergoing a minimally invasive hysterectomy. All women will receive acetaminophen either rectally or intravenously immediately postoperative, prior to extubation. Patient's will be randomly assigned to either the rectal acetaminophen or the intravenous acetaminophen group. Patient outcomes will be measured through a Numeric Rating Scale (NRS) from 0-10 for pain scores, and total opioid consumption measured in morphine milligram equivalent (MME) for the first 24 hours following surgery, or upon discharge, whichever comes first.

Patient's undergoing major gynecologic surgery require effective postoperative pain management in order to enhance recovery and ultimately allow patients to return to their preoperative functional state. Traditionally, acute postoperative pain control has been achieved largely with the use of opioid medications. Excessive use of opioids can have adverse effects on the recovery process. Side effects include, but are not limited to dizziness, sedation, nausea/vomiting, respiratory depression, euphoria, constipation, and abuse. In addition, opioid monotherapy can delay post-operative ambulation, contribute to prolonged hospital stay and resumption of activities of daily living, and furthermore, have long-term sequelae for individuals as well as society at whole.

Over the past decade, a multimodal approach to pain management has been explored in attempts to optimally treat acute postoperative pain. This approach is one of the keys to improving the recovery process.

Acetaminophen is a non-opioid analgesic with a well-established safety and tolerability profile that is commonly used in multimodal approach to treating surgical pain. It is available in oral, rectal and Intravenous (IV) formulation. IV acetaminophen in particular is increasingly used for pain control after surgery as it has demonstrated a significant analgesic benefit in a variety of surgery types by reduction in pain intensity while decreasing total opioid use. Many studies have evaluated the efficacy of acetaminophen based on route of administration. A systematic review demonstrated that there is no clear indication for intravenous acetaminophen for patients who can tolerate an oral dosage as there was no difference if efficacy outcomes. This is valuable information as the cost of IV acetaminophen is exponentially more than the oral form. Although the oral form of acetaminophen is as efficient as controlling pain when compared to IV, and is notably cheaper, it is not the best option for the nauseated patient or patients whom are restricted from oral intake following surgery. Rectal acetaminophen is therefore a feasible alternative option in such patients.

Data on the use of rectal acetaminophen in adults for postoperative pain management is limited. Pettersson and colleagues (2005) compared oral, rectal and IV paracetamol in day surgery patients. Although they demonstrated significantly higher plasma paracetamol concentrations in patients who received oral and IV formations at multiple time points, there was no difference in pain ratings. In another study, rectal paracetamol was shown to have a significant morphine-sparing effect after hysterectomy.

At this time, there has been no study in the gynecologic literature to compare IV to rectal acetaminophen in terms of pain control and effect on overall opioid use in the acute post-operative period.

The rationale for this study is to determine the optimal way of managing post-operative pain in gynecologic surgery in attempt to improve the overall recovery process. More specifically, this study will determine if the route of administration of acetaminophen has an effect on post-operative pain and use of opioid medication following a minimally invasive hysterectomy. The results of this study may guide post-operative pain management after gynecologic surgery, and help limit the amount of opioid use, while potentially reducing pharmacological costs for patients and hospitals.

Inclusion Criteria:

• Willing to consent
• Amendable to receive either rectal or intravenous acetaminophen
• Planned hospital stay for at least 24 hours.

Exclusion Criteria:

• Patients unable to provide informed consent
• Patients with a history of regular opioid use prior to surgery based on their current home medication list
• Patients who have required regular opioid intake for the 7 days preceding surgery
• Patients with known hypersensitivity to acetaminophen
• Patients with a baseline preoperative liver function enzymes (AST and ALT) that are greater than twice the upper limits
• Unable to complete procedure as planned.

From administration of acetaminophen until discharge from the hospital, up to 24 hours.

Due to the COVID-19 pandemic, many patients were prohibited to stay overnight in the hospital. Therefore, many patients were discharged home before 24 hours after surgery. This is primarily why the primary and secondary outcomes were analyzed at shorter time intervals (6 hours post-op and 12 hours-op) as well.