Changes to Medications Before Elective Surgery
Nil By Mouth (NBM)
Minimum fasting times for elective surgery (6-4-2):
- 6 hours for solid food
- 4 hours for breast milk
- 2 hours for clear fluids (e.g. water, tea / coffee without milk)
Note that being NBM is not a reason to omit regular oral medications; they can be given with a sip of water up to the time of surgery. See below for what oral medications need to be stopped.
Medications to Discontinue
The following are derived from a combination of both the BNF and the Handbook of Perioperative Medicines by the UK Clinical Pharmacy Association
- The BNF provides clear, specific guidance on the management of oestrogen-containing medications, ACE inhibitors/ARBs, lithium, and diabetes medications prior to surgery, so it is important to be familiar with these recommendations.
- For other drug classes, particularly antithrombotic agents (antiplatelets and anticoagulants), the BNF does not offer specific instructions. Instead, it advises that the anaesthetist and surgeon should jointly assess the patient’s individual risks and make case-by-case decisions about interruption or bridging (e.g., switching to heparin) based on both clinical and procedural factors.
- When not specifically mentioned in the BNF, information is derived from the Handbook of Perioperative Medicines
This is NOT an exhaustive list; always refer to local guidelines / protocol.
| Medication category | Specific medications | Changes to medicine | Rationale |
|---|---|---|---|
| Oestrogen-containing medications | COCPCombined oral contraceptive pill
* Discontinuation only recommended for oestrogen-containing contraception * Progesterone only hormonal contraception can be continued/started preoperatively (no increased thrombotic risk) |
Stop 4 weeks before surgery | Due to the increased risk of VTE from the oestrogen |
| HRTHormone replacement therapy | |||
| Cardiovascular medications | ACE inhibitor / ARB | Stop 24 hours before surgery | Due to the increased risk of hypotension |
| Potassium-sparing diuretic | May need to be stopped on the morning of surgery | Due to the increased risk of hyperkalaemia if renal perfusion is impaired or if there is tissue damage | |
| Other cardiovascular drugs like beta blockers, calcium channel blockers, and statins do NOT need to be stopped routinely before surgery. | |||
| Antiplatelets | Aspirin | If aspirin is used for analgesia → stop 7 days before surgery
If aspirin is used as an antiplatelet, it should generally be stopped 7 days before surgery, and take the following into consideration:
International guidelines: aspirin should be stopped before surgery for primary prevention, but continued for secondary prevention |
Due to the increased risk of bleeding |
| P2Y12 inhibitors | Clopidogrel / prasugrel: stop 7 days before surgery
Ticagrelor: stop 5 days before surgery |
||
| Anticoagulants | Warfarin | Stop 5 days before surgery
Bridging with heparin is necessary for those at high thromboembolic riskExamples include mechanical heart valve, atrial fibrillation, recent VTE |
|
| LMWHLow molecular weight heparin (e.g. enoxaparin, dalteparin) | Stop 12 hours (prophylactic dose) / 24 hours (treatment dose) before surgery | ||
| DOACsDirect oral anticoagulants (e.g. apixaban, rivaroxaban, edoxaban)* | If patient is on DOAC due to recent DVT / PE → consult haematology
Otherwise, it depends on bleeding risk of surgery / procedure
|
||
| Psychiatric medications | Lithium | Stop 24 hours before major surgery
Otherwise, it can be continued for minor surgery |
Due to its interaction with muscle relaxants (potentiates their effect) and the risk of lithium toxicity |
| Clozapine | Stop 12 hours before surgery | To minimise the risk of hypotension and sedation without risking relapse | |
| Diabetes medications | See separate section below | ||
*Decisions regarding stopping anticoagulants are more complicated, require individualisation and balancing between the indications for anticoagulation and risk of bleeding. Therefore, certain details are omitted for educational purposes.
Generally, when it comes to stopping antiplatelets or anticoagulants before elective surgeries, the decision is not that clean-cut.
Medications to Increase / Continue as Normal
People on long-term steroids (for adrenal insufficiency or other reasons) should receive ‘stress’ glucocorticoid doses to prevent adrenal crisis during surgery (a stress event)
- When patients are NBM, switch to IV hydrocortisone at stress doses (usually double the daily dose)
Otherwise, the BNF advised specifically that the following drugs should NOT be stopped before surgery:
- Antiepileptics
- Antiparkinsonian drugs
- Antipsychotics
- Anxiolytics
- Bronchodilators
- Cardiovascular drugs (apart from ACE inhibitors / ARBs / potassium-sparing diuretics, mentioned above)
- Glaucoma drugs
- Immunosuppressants
- Drugs of dependence
- Thyroid / antithyroid drugs
Pre-Operative Management of Diabetes Mellitus
Emergency Surgery
Most people with diabetes (type 1 and 2) requiring emergency surgery should receive VRIII protocol VRIII: variable rate intravenous insulin infusion VRIII is a protocol for administering short-acting insulin (e.g. Actrapid, Humulin R) intravenously: To prevent hypoglycaemia and hypokalaemia (from the insulin):
(regardless of whether they are taking insulin or not)
Regarding changes to other medications, it is the same as those for elective surgery, summarised here:
- If the patient takes insulin → continue long-acting insulin at 80% normal dose + stop any other insulin
- If patients take oral medications
- Stop sulfonylurea + SGLT-2 inhibitors
- Stop metformin if >1 meal will be missed or at significant risk of developing AKI (eGFR <60 or procedure involves use of contrast media)
- Other diabetic drugs can be continued (DPP-4 inhibitors, pioglitazone, GLP-1 agonist)
Elective Surgery
Patients Who Only Take Oral Medications
In patients who only take oral medications (i.e. most type 2 diabetes patients), there are 2 things to consider:
- Changes to regular oral medications
- Whether starting VRIII protocol
VRIII: variable rate intravenous insulin infusion
VRIII is a protocol for administering short-acting insulin (e.g. Actrapid, Humulin R) intravenously:
- The insulin is mixed with 0.9% NaCl.
- Typical preparation: 50 units of insulin in 50mL of 0.9% NaCl (1 unit / mL)
- The infusion rate is adjusted based on frequent capillary blood glucose measurements. The goal is to maintain blood glucose within a tightly controlled target range (typically 6-10 mmol/L)
To prevent hypoglycaemia and hypokalaemia (from the insulin):
- 5% glucose in 0.45% NaCl and 0.15%/0.3% KCl should always run alongside at a rate to meet the patient’s fluid maintenance requirements
- IV glucose 20% should be given if blood glucose <6 mmol/L
1. Changes to Regular Oral Medications
The key concept here is: ALWAYS take the drugs normally before admission, ONLY make any changes on the day of surgery
| Drug | Changes prior to surgery |
|---|---|
| Metformin | Omit the metformin on the day if:*
Such that, it is possible to continue metformin (and just omitting the lunchtime dose if prescribed TDS) if 1) only 1 meal will be missed, 2) eGFR >60, and 3) low risk of AKI. * This is due to the increased risk of lactic acidosis intra-operatively and post-operatively (as the patient would be relatively dehydrated and surgery is a stressful event) |
| Sulfonylurea | NB sulfonylureas carry a significant risk of hypoglycaemia:
|
| SGLT-2 inhibitors | Omit on the day (due to risk of DKA) |
| Pioglitazone | Take as normal (no need to omit) |
| DPP-4 inhibitors | |
| GLP-1 agonist* |
*One might encounter a source saying that GLP-1 agonists should be stopped 1 week before surgery (endorsed by US guidelines), due to the increased risk of aspiration (GLP-1 agonists delay gastric emptying). However, both the BNF and Association of Anaesthetists (Jan 2025) advise that GLP-1 or dual GIP/GLP-1 receptor agonists can be taken as normal before surgeries. [Ref]
2. Whether Starting VRIII is Necessary or Not
The VRIII protocol VRIII: variable rate intravenous insulin infusion VRIII is a protocol for administering short-acting insulin (e.g. Actrapid, Humulin R) intravenously: To prevent hypoglycaemia and hypokalaemia (from the insulin):
should be started if (ANY):
- Patient undergoing a major procedure (i.e. long fasting period causing >1 missed meal)
- Patient with suboptimal diabetes management (defined as HbA1c >69 mmol/mol or >8.5%)
- Patients with persistent pre-operative hyperglycaemia (defined as capillary blood glucose >12 mmol/L) (usually in the context of acute decompensation)
Patients Who Take Insulin
Pre-Op – Management of Insulin Therapy
Pre-op management largely depends on 1) procedure type (minor vs major) and 2) glycemic control (good vs poor)
| Procedure type definitions |
|
| Glycaemic control definitions |
|
Based on the above factors, there are 2 scenarios.
Good Glycaemic Control AND Undergoing a Minor Procedure
There is NO need to give additional insulin (i.e. VRIII protocol VRIII: variable rate intravenous insulin infusion VRIII is a protocol for administering short-acting insulin (e.g. Actrapid, Humulin R) intravenously: To prevent hypoglycaemia and hypokalaemia (from the insulin):
) in these patients; they can be managed by adjusting their usual insulin regimen on the day before surgery:
- Once-daily long-acting insulin → give 80% of the usual dose (20% dose reduction)
- All other insulin → give as normal
Poor Glycaemic Control OR Undergoing a Major Procedure
These patients require additional insulin, the exact steps are:
| Phase | Action |
|---|---|
| The day before surgery |
|
| On the day of surgery |
|
Post-Op – Converting Back to Normal (Subcutaneous) Insulin
Conversion back to normal subcutaneous insulin should NOT begin until the patient is eating and drinking without nausea and vomiting.
There are 3 main scenarios:
| Scenario (depends on the patient’s previous insulin regimen) | Conversion |
|---|---|
| Basal-bolus regimen (the typical T1DM regimen) |
|
| Twice-daily mixed insulin regimen |
|
| Once-daily long-acting insulin |
Remember, once-daily long-acting insulin does NOT need to be stopped pre-op (only dose reduction) |
References
NICE BNF Treatment summaries Surgery and long-term medication
NICE BNF Treatment summaries Diabetes, surgery and medical illness
UK Clinical Pharmacy Association - Handbook of Perioperative Medicines