Insulin

Question 1

Indications

Answer 1

1. For insulin replacement in people with type 1 diabetes mellitus and control of blood glucose in people with type 2 diabetes mellitus where oral hypoglycaemic treatment is inadequate or poorly tolerated.
2. Given intravenously, in the treatment of diabetic emergencies such as diabetic ketoacidosis and hyperglycaemic hyperosmolar syndrome, and for perioperative glycaemic control in selected diabetic patients.
3. Alongside glucose to treat hyperkalaemia, while other measures (such as treatment of the underlying cause) are initiated.

Question 2

Mechanisms of action

Answer 2

For the treatment of hyperkalaemia, insulin drives K+ into cells, reducing serum K+ concentrations. However, once insulin treatment is stopped, K+ leaks back out of the cells into the circulation, so this is a short-term measure while other treatment is commenced.

Question 3

Adverse effects

Answer 3

The main adverse effect of insulin is hypoglycaemia, which can be severe enough to lead to coma and death. When administered by repeated subcutaneous (SC) injection at the same site, insulin can cause fat overgrowth (lipohypertrophy), which may be unsightly or uncomfortable.

Question 4

Warnings

Answer 4

In patients with renal impairment, insulin clearance is reduced, so there is an increased risk of hypoglycaemia.

Question 5

Interactions

Answer 5

Although often necessary, combining insulin with other hypoglycaemic agents increases the risk of hypoglycaemia. Concurrent therapy with systemic corticosteroids increases insulin requirements.

Question 6

Prescription

Answer 6

In diabetes mellitus, patients may self-administer regular insulin by SC injection. The goal of treatment is to attain good blood glucose control without problematic hypoglycaemia. Insulin treatment is prescribed in units. Normal daily requirement is ~30–50 units, although this varies considerably between individuals, depending on weight, diet and activity. Treatment usually includes once or twice daily long-acting insulin to meet basal requirements, with intermittent rapid or short-acting insulin injected with meals to control post-prandial glucose.

Question 7

Administration

Answer 7

SC insulin is often administered using ‘pens’ containing insulin in solution (100 units/mL). These allow a patient to ‘dial up’ the number of units required and administer insulin discreetly, e.g. through clothes.

Question 8

Communication

Answer 8

When starting a patient with diabetes mellitus on insulin, explain that insulin will help to control blood sugar levels and prevent complications. Advise them that lifestyle measures, including a calorie-controlled diet and regular exercise, are needed as well as insulin to improve health. Warn them of the risk of hypoglycaemia, advising them of symptoms to watch out for (e.g. dizziness, agitation, nausea, sweating and confusion). Explain that, if hypoglycaemia develops, they should take something sugary (e.g. glucose tablets or a sugary drink) then something starchy, e.g. a sandwich.

Question 9

Monitoring

Answer 9

Patients should measure capillary blood glucose regularly and adjust insulin dose based on results. HbA1c (glycated haemoglobin) should be measured at least annually to assess long-term glycaemic control. Where insulin is given as a continuous IV infusion, serum K+ should be measured at least every 4 hours to guide need for replacement.