UK Clinical Pharmacy Association

Insulin – Self-mixed

Brands of self-mixed insulin

Self-mixed insulin refers to two different types of insulin (usually a short-acting and intermediate-acting insulin) combined by the patient into one injection.


Actrapid®, Apidra®, Fiasp®, Humalog®, Humulin® S, Hypurin® Porcine Neutral, NovoRapid® 


Humulin® I, Hypurin® Porcine Isophane Insulatard®, Insuman® Basal

Issues for surgery

Hypoglycaemia if continued during nil by mouth period/during liver reduction diet (LRD) in patients undergoing bariatric surgery.

Increased risk of post-operative infection and delayed wound healing due to poor glycaemic control if discontinued.

Advice in the perioperative period

Insulin products are classified according to their duration of action and it is important to understand the type of insulin the patient is on in relation to the advice to be given perioperatively. Confirm with the patient the exact name, strength, dose, frequency and preparation of insulin(s) that they are using (see Further Information).

Elective surgery 

Stop short-acting insulin and adjust dose of intermediate-acting insulin on day of operation - see table for details of dose adjustment.

Except patients undergoing bariatric surgery – see below.

When reducing insulin doses round to the nearest unit.

RegimenDay before procedureDay of procedure*

TWICE daily

No dose change
Calculate the total dose of both morning insulins and give half of this total dose as intermediate-acting insulin only in the morning

Check capillary blood glucose (CBG) on admission

* Advice is the same for MORNING and AFTERNOON procedure

Patients undergoing bariatric surgery

Patients with type 1 diabetes mellitus need an individualised management plan formulated with the diabetes specialist team.

Patients with type 2 diabetes mellitus commencing on liver reduction diet (LRD), give 50% of usual dose of intermediate-acting insulin when LRD commences, with close monitoring of CBG (see Further information). Stop regular administration of short-acting insulin when LRD commences. If CBG greater than 15mmol/L give 50% of usual dose of short-acting insulin as a rescue/correction dose. When reducing insulin doses round to the nearest unit.

Patients with type 2 diabetes mellitus not following a LRD, follow the advice above for Elective surgery.

Emergency surgery 

Monitor CBG, ketones, renal profile and lactate on admission to exclude DKA or hyperosmolar hyperglycaemic state (HHS). The advice given above can be applied to patients presenting for emergency surgery; however, it must be remembered that these patients are high risk and are likely to require intravenous insulin infusion; either variable rate intravenous insulin infusion (VRIII), or in the case of DKA or HHS a fixed rate intravenous insulin infusion – see Further information. Continue to monitor ketones if CBG greater than 13mmol/mol.

Perioperative considerations

Commence variable rate intravenous insulin infusion (VRIII) perioperatively where indicated, omit patient’s usual self-mixed insulin, and commence a long-acting insulin at a dose of 0.2 units per kilogram (see above and Further information).

Ensure emergency treatment of hypoglycaemia is prescribed, i.e. Glucogel® and 20% dextrose. Rapid acting insulin should also be prescribed.

Post-operative advice

Encourage an early return to normal eating and drinking (as deemed appropriate by the surgical team), facilitating return to the patient’s usual diabetic regimen. The insulin dose(s) may need adjusting, as insulin requirements can change due to post-operative stress, infection or altered food intake – monitor CBG levels and seek advice from specialist diabetes team if necessary.

Ideally, resume usual evening insulin if eating a normal meal. If eating a half or small meal give half usual dose. If not eating, only give intermediate-acting component of the usual mixed insulin.

If VRIII being used: Stop until eating and drinking and replace with a long-acting insulin at a dose of 0.2 units per kilogram.

Patients undergoing bariatric surgery

Improved glycaemic control is expected because of reduced calorie intake, early satiety and weight loss following bariatric surgery.

Patients with type 1 diabetes mellitus should be reviewed by the diabetes specialist team post-operatively.

Patients with type 2 diabetes should hold their self-mixed insulin post-operatively. Blood glucose should be monitored until eating habits and food intake stabilises. Patients should have their need for ongoing pharmacological management of their diabetes reviewed by their GP or bariatric surgical team.

Interactions with common anaesthetic agents

Reduction of blood-glucose lowering effect

Substances that may reduce the blood-glucose-lowering effect include sympathomimetics (e.g. epinephrine/adrenaline).

Interactions with other common medicines used in the perioperative period

Enhancement of blood-glucose lowering effect

Substances that may enhance the blood-glucose lowering effect of insulin and increase susceptibility to hypoglycaemia include sulphonamide antibiotics (e.g. co-trimoxazole).

Reduction of blood-glucose lowering effect

Corticosteroids can reduce the blood-glucose-lowering effect of insulin. Clinically important hyperglycaemia has been seen. Monitor CBG closely when corticosteroids are given to patients with diabetes.

Somatostatin analogues (octreotide and possibly lanreotide) may either increase or decrease the insulin requirements but most patients with type 1 diabetes are likely to require a reduction in insulin dose, with some studies suggesting a potential reduction of 50% in patients taking concomitant octreotide. Monitor CBG when somatostatin analogues are given to patients with diabetes.

Further information

Safe prescribing and administration of insulin

Insulin should be prescribed according to National Patient Safety Agency (NPSA) recommendations for safe use of insulin, with the brand name and units written in full.

Patients and nursing staff should be reminded of the importance of rotating injection sites within the same body region to reduce or prevent the risk of cutaneous amyloidosis and other skin reactions; injecting into an affected ‘lumpy’ area may reduce the effectiveness of insulin.

Variable rate insulin infusion (VRIII)

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 (although VRIII may be necessary in patients with type 1 diabetes who have not received their long-acting insulin, in patients with type 1 diabetes who are expected to miss more than one meal, if emergency surgery or in people with poorly controlled diabetes (HbA1c greater than 69mmol/mol)). Patients with type 2 diabetes who are expected to miss more than one meal should have VRIII if they develop hyperglycaemia (CBG greater than 12mmol/L).

Commence a long-acting insulin at 0.2 units per kilogram during treatment with VRIII to prevent hyperglycaemia and ketosis on cessation of VRIII. In patients with type 1 diabetes do not discontinue VRIII unless patient has received alternative subcutaneous insulin within the last 30 minutes.

Liver reduction diet (LRD)

Most people needing bariatric surgery have a large, fatty liver which can cause difficulty for laparoscopic surgery, as the stomach cannot be easily accessed. The LRD typically starts 10 – 15 days prior to bariatric surgery and is based on low calories, in particular low carbohydrate and fat. This forces stored glycogen to be released from the liver (plus some water), making it softer, more flexible and easier to move. Due to the reduced calorie and carbohydrate intake, CBG levels will most likely be reduced. Patients are at increased risk of hypoglycaemia when the usual dose of self-mixed insulin is continued during this period.


Centre for Perioperative Care. Guideline for Perioperative Care for People with Diabetes Mellitus Undergoing Elective and Emergency Surgery (March 2021). Available at: [Accessed on 8th March 2021]

Busetto L, Dicker D, Azran C et al. Practical Recommendations of the Obesity Management Task Force of the European Association for the Study of Obesity for the Post-Bariatric Surgery Medical Management. Obesity Facts 2017;10:597 – 632. DOI: 10.1159/000481825

Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press. [Accessed on 1st March 2021]

Summary of Product Characteristics – Actrapid® (human insulin) 100 international units/ml, Solution for Injection in a vial. Novo Nordisk Limited. Accessed via 01/03/2021 [date of revision of the text October 2020]

Summary of Product Characteristics – Hypurin® Porcine Neutral (porcine insulin) Cartridges – PL 29831/0124. Wockhardt UK Ltd. Accessed via 01/03/2021 [date of revision of the text September 2020)

Summary of Product Characteristics – Fiasp® (insulin aspart) 100 units/mL Penfill solution for injection in cartridge. Novo Nordisk Limited. Accessed via 01/03/2021 [date of revision of the text October 2020]

Summary of Product Characteristics – Apidra® (insulin glulisine) SoloStar 100 Units/ml solution for injection in a pre-filled pen. SANOFI. Accessed via 01/03/2021 [date of revision of the text September 2020]

Insulin. In: Brayfield A (Ed), Martindale: The Complete Drug Reference. London: The Royal Pharmaceutical Society of Great Britain. [Accessed 1st March 2021] 

Summary of Product Characteristics – HUMULIN® I (human insulin) KwikPen (Isophane) 100IU/ml suspension for injection. Eli Lilly and Company Limited. Accessed via 01/03/2021 [date of revision of the text October 2020]

Baxter K, Preston CL (eds), Stockley’s Drug Interactions (online) London: Pharmaceutical Press. [Accessed on 1st March 2021]