Insulin (Soluble / Actrapid)

How it works

Soluble insulin replaces endogenous insulin, promoting cellular glucose uptake, suppressing hepatic glucose output, and driving potassium into cells; given subcutaneously it has a slower onset and longer duration than rapid-acting analogues.

Prescribing in practice

• The most important safety point is the risk of hypoglycaemia, compounded by insulin being a high-alert medicine prone to prescribing and administration errors, so use insulin-specific syringes and never abbreviate units as 'U'.
• When given subcutaneously before meals, allow an adequate interval between injection and eating because onset is slower than analogue insulins.
• Intravenous variable-rate infusions require close glucose and potassium monitoring with a clear protocol.

Monitoring

Monitor capillary or laboratory blood glucose, and potassium when given intravenously, adjusting the regimen to avoid hypoglycaemia.

Counselling the patient

• Recognise and treat hypoglycaemia promptly and always carry a fast-acting source of sugar.
• Inject a short time before meals as advised, and rotate injection sites to avoid lipohypertrophy.
• Never change insulin type or strength without specialist advice.

Evidence & guidelines

Insulin is identified by the MHRA/NHS as a high-alert medicine, and intensive glycaemic control with insulin reduced complications in landmark trials such as DCCT and UKPDS.