Insulin regimens in insulin-dependent diabetes mellitus

In the normal individual insulin is secreted into the portal circulation in response to glucose, glucagon, amino acids, fatty acids and gastrointestinal hormones. Its secretion is inhibited by somatostatin, dopamine and sympathetic nervous stimulation. In short the secretion of insulin represents a complex homeostatic mechanism.

Obviously the delivery of exogenous insulin cannot be so tightly controlled and indeed none of the insulin regimens in use today deliver insulin to the portal circulation or modify insulin supply in response to even blood glucose concentration. Exogenous insulin is simply injected subcutaneously from where it is absorbed into the systemic circulation. A number of preparations of insulin have been developed with different pharmacokinetic properties and a number of insulin regimens designed attempting to mimic as much as is possible the pattern of insulin secretion in a normal individual eating a normal diet on a normal day !

The absorption of insulin given subcutaneously is associated with wide intraindividual (25%) and interindividual (50%) variability. A number of factors affect insulin absorption including:

• type and species of origin of insulin.
• site and depth of injection.
• factors affecting local blood flow;
  • exercise
  • massage
  • skin Temperature Examples insulin regimens are:
• twice daily injection of a mixture of short and intermediate acting insulins.
• once or twice daily injection of an intermediate or long acting insulin with 3 or 4 injections of a short acting insulin before meals
• constant subcutaneous infusion of short acting insulin by means of an infusion pump (CSII).