A POLYPEPTIDE hormone (see HORMONES) produced in the PANCREAS by the beta cells of the ISLETS OF LANGERHANS. It plays a key role in the body’s regulation of CARBOHYDRATE, FAT, and PROTEIN, and its de?ciency leads to DIABETES MELLITUS. Diabetic patients are described as type 1 (insulin dependent), or type 2 (non-insulin dependent), although many of the latter may need insulin later on, in order to maintain good control.
Insulin is extracted mainly from pork pancreas and puri?ed by crystallisation; it may be made biosynthetically by recombinant DNA technology using Escherichia coli, or semisynthetically by enzymatic modi?cation of porcine insulin to produce human insulin. The latter is the form now generally used, although some patients ?nd it unsuitable and have to return to porcine insulin.
The hormone acts by enabling the muscles and other tissues requiring sugar for their activity to take up this substance from the blood. All insulin preparations are to a greater or lesser extent immunogenic in humans, but immunological resistance to insulin action is uncommon.
Previously available in three strengths, of 20, 40, and 80 units per millilitre (U/ml), these have now largely been replaced by a standard strength of 100 U/ml (U100). Numerous different insulin preparations are listed; these differ in their speed of onset and duration of action, and hence vary in their suitability for individual patients.
Insulin is inactivated by gastrointestinal enzymes and is therefore generally given by subcutaneous injection, usually into the upper arms, thighs, buttocks, or abdomen. Some insulins are also available in cartridge form, which may be administered by injection devices (‘pens’). The absorption may vary from di?erent sites and with strenuous activity. About 25 per cent of diabetics require insulin treatment: most children from the onset, and all patients presenting with ketoacidosis. Insulin is also often needed by those with a rapid onset of symptoms such as weight loss, weakness, and sometimes vomiting, often associated with ketonuria.
The aim of treatment is to maintain good control of blood glucose concentration, while avoiding severe HYPOGLYCAEMIA; this is usually achieved by a regimen of preprandial injections of short-acting insulin (often with a bedtime injection of long-acting insulin). Insulin may also be given by continuous subcutaneous infusion with an infusion pump. This technique has many disadvantages: patients must be well motivated and able to monitor their own blood glucose, with access to expert advice both day and night; it is therefore rarely used.
Hypoglycaemia is a potential hazard for many patients converting from porcine to human insulin, because human insulin may result in them being unaware of classical hypoglycaemic warning symptoms. Drivers must be particularly careful, and individuals may be forbidden to drive if they have frequent or severe hypoglycaemic attacks. For this reason, insurance companies should be warned, and diabetics should – after taking appropriate medical advice – either return to porcine insulin or consider stopping driving.... insulin
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