Insulin is the primary treatment for all patients with type I diabetes and for type II diabetic patients not adequately controlled by diet and/or oral hypoglycaemic agents.
Very rapidly acting insulins include the injectable insulin aspart, insulin glulisine and insulin lispro. The injectable insulins have a very rapid onset of action of between 4 and 20 minutes, allowing administration shortly before or after a meal. Their duration of action of 2 to 5 hours is shorter than that of soluble insulin. A consequence of their very rapid action is that if hyperglycaemia does occur, it may occur earlier after an injection when compared with soluble insulin. In children, very rapidly acting injectable insulins should only be used in preference to soluble insulin when a fast onset of action might be beneficial, for example in the timing of injections in relation to meals.
Short-acting insulins include acid and neutral soluble preparations. They have a quick onset, a duration of action up to approximately 8 hours, and a peak between 2 and 4 hours.
Intermediate and long-acting insulins include isophane insulin and insulin zinc suspension. They have an onset of action of approximately 1-4 hours and their effects can last up to 35 hours. Insulin glargine is a long-acting insulin analogue that precipitates in the neutral pH of the subcutanous compartment following injection, forming a depot from which insulin monomers are slowly absorbed. This gives a delayed (1.5 hours) and prolonged (24 hours) absorption profile with no pronounced peaks. Insulin degludec forms soluble multi-hexamers upon subcutaneous injection; these also act as a depot from which insulin monomers are gradually released. The glucose-lowering effect lasts over 42 hours, allowing flexibility in the time of administration. The prolonged action of insulin detemir is mediated by strong self-association of the molecules at the injection site and albumin binding via the fatty acid side-chain, which result in slow distribution to peripheral target tissues.
Biphasic insulins are stable premixed preparations containing fixed proportions of neutral soluble and isophane insulins which give a biphasic action. Speed of onset depends on the proportion of soluble insulin.