Mounjaro (tirzepatide) is a GLP-1 and GIP receptor agonist used for type 2 diabetes and weight management in the UK. When to resume Mounjaro after surgery depends on the procedure type, recovery progress, and gastrointestinal function. Surgical teams typically advise waiting until normal eating resumes and bowel function returns before restarting treatment. This article examines UK practice guidance on safely resuming Mounjaro post-operatively, factors affecting timing, and strategies for managing blood glucose during treatment interruption, helping patients and clinicians navigate perioperative tirzepatide management.

Why Mounjaro Is Stopped Before Surgery

Mounjaro (tirzepatide) is a glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptor agonist licensed in the UK for the treatment of type 2 diabetes mellitus. Tirzepatide is also available under the brand name Zepbound for weight management in adults with obesity or overweight with weight-related comorbidities. The medication works by slowing gastric emptying, enhancing insulin secretion, and reducing appetite. Whilst these mechanisms provide significant metabolic benefits, they may create specific perioperative considerations that sometimes necessitate temporary discontinuation before surgical procedures.

A key consideration relates to delayed gastric emptying, which may increase the risk of pulmonary aspiration during anaesthesia. When gastric contents remain in the stomach for prolonged periods, patients undergoing general anaesthesia could face a heightened risk of regurgitation and aspiration of gastric material into the lungs, potentially causing aspiration pneumonitis or pneumonia. This complication can be serious and may prolong hospital recovery. Current UK practice, as outlined in the Centre for Perioperative Care (CPOC) guidance and UK Clinical Pharmacy Association (UKCPA) Handbook of Perioperative Medicines, generally advises that weekly GLP-1 receptor agonists can be continued before elective surgery with standard fasting, but individualised assessment is recommended for patients with significant gastrointestinal symptoms or high aspiration risk.

Additionally, Mounjaro can cause gastrointestinal adverse effects including nausea, vomiting, and diarrhoea, which may complicate post-operative recovery and fluid management. The medication's effects on gastric motility persist beyond the immediate dosing period, with tirzepatide having a half-life of approximately five days according to the Summary of Product Characteristics. The decision to continue or temporarily stop treatment should balance glycaemic control against the potential for gastrointestinal effects during the perioperative period, and should follow local hospital policies and multidisciplinary assessment.

When to Resume Mounjaro After Surgery: UK Practice Considerations

UK practice regarding tirzepatide in the perioperative period varies, with decisions typically individualised based on the type and complexity of the surgical procedure, the patient's symptoms, and local hospital policies. For elective operations, the UKCPA Perioperative Medicines Handbook and CPOC guidance generally advise that weekly GLP-1 receptor agonists can be continued before surgery with standard fasting protocols, though individualisation is recommended for patients with significant gastrointestinal symptoms or those at high risk of aspiration. Emergency surgery presents different challenges, requiring anaesthetists to implement additional aspiration precautions.

Resuming Mounjaro after surgery requires careful consideration of several clinical factors. For minor procedures performed under local anaesthesia with no gastrointestinal involvement, patients may typically restart Mounjaro once they have resumed normal oral intake and are tolerating food and fluids without nausea or vomiting. However, for more extensive operations, particularly those involving the gastrointestinal tract, abdominal cavity, or requiring general anaesthesia, a more cautious approach is warranted.

Most surgical teams recommend waiting until bowel function has returned to normal, evidenced by the passage of flatus or stool, and the patient is eating and drinking normally without gastrointestinal symptoms. The timing varies depending on the procedure and individual recovery. Patients should have explicit clearance from their surgical team before restarting Mounjaro, as premature resumption could exacerbate post-operative nausea or delay recovery of gut motility. After a prolonged interruption, patients may need to re-initiate treatment at a lower dose and up-titrate according to the prescriber's guidance, as outlined in the Mounjaro Summary of Product Characteristics. The prescribing clinician or diabetes specialist nurse should be consulted to confirm the appropriate timing and dosing for individual patients, particularly those with complex medical histories or those who experienced surgical complications.

Factors That Affect Restarting Mounjaro Post-Operatively

Multiple patient-specific and surgical factors influence the decision regarding when to safely resume Mounjaro following an operation. The type and extent of surgery represent primary considerations. Minor superficial procedures such as skin lesion excisions or dental work typically allow earlier resumption compared with major intra-abdominal operations like bowel resections, bariatric surgery, or gynaecological procedures. Operations involving the gastrointestinal tract require particular caution, as Mounjaro's effects on gastric motility could potentially interfere with surgical healing or the identification of post-operative complications such as ileus or obstruction.

The patient's overall recovery trajectory significantly impacts timing. Individuals experiencing post-operative complications including infection, delayed wound healing, persistent nausea, or prolonged ileus should defer restarting Mounjaro until these issues resolve. The presence of nausea or vomiting suggests deferring resumption, as Mounjaro may exacerbate these symptoms. Adequate pain control is also relevant, as opioid analgesics themselves slow gastric emptying and combining them with Mounjaro may compound gastrointestinal adverse effects.

Pre-existing diabetes control and the urgency of resuming glucose-lowering therapy must be balanced against surgical recovery. Patients with well-controlled type 2 diabetes may safely delay restarting Mounjaro until post-operative recovery is well established, using alternative shorter-acting medications if needed. Conversely, those with poor baseline glycaemic control or significant hyperglycaemia during the perioperative period may require earlier resumption or bridging with insulin therapy. Renal function assessment is prudent before restarting medications, particularly after major surgery or in patients who experienced acute kidney injury, dehydration, or significant fluid shifts, though tirzepatide itself does not require routine renal dose adjustment. Individual tolerance to Mounjaro prior to surgery also matters; patients who previously experienced significant gastrointestinal adverse effects may benefit from a more gradual reintroduction or temporary dose reduction when resuming treatment post-operatively, in line with the prescriber's guidance.

Managing Blood Sugar While Off Mounjaro

Maintaining adequate glycaemic control during the perioperative period whilst Mounjaro is withheld requires proactive planning and often necessitates temporary alternative glucose-lowering strategies. For patients with type 2 diabetes, the approach depends on baseline diabetes control, the presence of other glucose-lowering medications, and the nature of the surgical procedure. Patients taking Mounjaro alongside metformin may continue metformin throughout the perioperative period unless contraindicated by acute kidney injury, dehydration, or the use of iodinated contrast media. Metformin should be withheld on the day of surgery if the patient is fasting, and should not be restarted until normal renal function is confirmed, particularly after procedures using contrast agents.

For individuals whose diabetes was well-controlled on Mounjaro monotherapy, close blood glucose monitoring becomes essential during the treatment interruption. Patients should be advised to check capillary blood glucose levels at least twice daily, or more frequently if they develop symptoms of hyperglycaemia such as increased thirst, polyuria, or fatigue. According to CPOC guidance, perioperative target glucose levels typically aim for 6-10 mmol/L (with 4-12 mmol/L considered acceptable). If blood glucose levels consistently exceed 12 mmol/L or the patient develops symptoms of significant hyperglycaemia, urgent contact with their diabetes care team or GP is necessary. For glucose levels above 20 mmol/L, or if ketones are present, emergency care should be sought.

Some patients may require temporary bridging therapy with short-acting glucose-lowering medications. Sulfonylureas are usually omitted on the day of surgery to reduce hypoglycaemia risk. Basal insulin or a short course of intermediate-acting insulin may be initiated under specialist guidance, particularly for those undergoing prolonged surgical recovery or experiencing significant stress hyperglycaemia. Hospital inpatients typically receive variable rate intravenous insulin infusions during major surgery, transitioning to subcutaneous insulin regimens post-operatively until oral intake resumes and Mounjaro can be safely restarted, as outlined in CPOC guidance. Patients using tirzepatide for weight management (Zepbound) rather than diabetes should focus on maintaining healthy eating patterns during the interruption period, though significant metabolic decompensation is less likely in this population. Clear communication between surgical teams, diabetes specialists, and primary care clinicians ensures coordinated management and prevents gaps in glucose monitoring or treatment during this vulnerable period.

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