Issues for Surgery
For patients with diabetes – increased risk of post-operative infection and delayed wound healing due to poor glycaemic control if omitted.
Risk of lactic acidosis if continued (see Further Information).
Potential for hypoglycaemia when taken concomitantly with other blood glucose lowering medicines and continued during nil by mouth period.
Advice in the Perioperative period
Metformin should be taken as normal the day prior to surgery (including any combination products)1.
Morning or Afternoon Surgery
If eGFR > 60 ml/min/1.73m2: -
If eGFR < 60 ml/min/1.73m2: -
This advice should also be followed for: -
Consideration should be given to prescribing the components of combination products as separate medicines perioperatively.
In the event of emergency surgery and the patient has already taken their metformin dose(s). Monitor blood glucose levels closely and treat any hypoglycaemia accordingly.
Commence variable rate intravenous insulin infusion (VRIII) perioperatively where indicated (see Further Information) and omit metformin during VRIII treatment1.
Ensure emergency treatment of hypoglycaemia is prescribed i.e. Glucogel® and 20% dextrose. Rapid acting insulin should also be prescribed1, 2.
Check renal function post-operatively; once eating and drinking normally and VRIII (where applicable) has been stopped1 follow the advice below:-
Interaction(s) with Common Anaesthetic Agents
None2, 3, 4, 5.
Interaction(s) with other Common Medicines used in the Perioperative Period
Iodinated Contrast Agents
Iodinated contrast agents can cause contrast-induced nephropathy (CIN). If CIN occurs, this can result in metformin accumulation and increased risk of lactic acidosis, although there is a lack of any valid evidence3, 4, 5, 6. Ensure that renal function is checked prior to administration of iodinated contrast agents.
Non-Steroidal Anti-inflammatory Drugs (NSAIDs)
Care with concomitant use of NSAIDs due to risk of impaired renal function and subsequent increased risk of lactic acidosis2, 3, 4, 5.
Lactic acidosis is a very rare but serious metabolic complication, which most often occurs at acute worsening of renal function or cardiorespiratory illness or sepsis. Metformin accumulation occurs as renal function deteriorates and increases the risk of lactic acidosis. Other risk factors include dehydration and prolonged fasting2, 3, 4.
It should be noted that most manufacturers advise that metformin / metformin-containing products should be discontinued for all patients at the time of surgery under general, spinal or epidural anaesthesia, including those patient receiving iodinated contrast agents; and restarted no earlier than 48 hours after on resumption of oral nutrition and where renal function has been checked and is stable3, 4, 5. However, current national guidance does not support this general restriction in patients with an eGFR > 60ml/min/1.73m2 and the advice above should be followed1, 6.
Patients with a planned short starvation period (no more than one missed meal in total) should be managed by modification of their usual diabetes medication, avoiding VRIII wherever possible. Patients expected to miss more than one meal should have VRIII1.
NB: patients on ONCE DAILY metformin, should only start VRIII if their capillary blood glucose levels are > 12mmol/L on 2 consecutive occasions1.
Use of VRIII is not indicated for patients taking metformin for PCOS.