Insulin therapy - Diabetes mellitus

Insulin therapy

Synthetic insulin is administered subcutaneously in a variety of regimens. Various insulins have been ‘designed’ with different pharmacokinetic effects (see Table 11.17).

Two common regimens are used (see Fig. 11.15):

·        A twice daily adminstration of biphasic insulin, with two thirds of the total daily dose given before breakfast and one third given before the evening meal.

·        A bolus of short or immediate acting insulin given three times a day at meal times and a medium or long-acting insulin given at night. The advantage of this regimen is that meal times and quantities can be varied. If immediate acting insulin is used it is taken at or immediately after the meal, if short acting is used then this is administered 30 minutes before the meal.

A continuous subcutaneous insulin infusion or continuous intravenous infusion via a tunelled line may also be used. An infusion pump controls the rate and preprandial boosts can be given simply and easily. They are expensive and if they fail, they can cause diabetic ketoacidosis, as there is no longeracting reserve.

The site of injection also affects the absorption rate:

·        The abdominal wall is quickest (use before meal-times).

·        The arms are intermediate.

·        The legs are the slowest (night-time).

Temperature and exercise affect absorption. Exercise also increases the use of glucose and hence reduces the amount of insulin needed. Patients must be educated about the problems with insulin therapy. For example, common sites of injection may develop fat hypertrophy or fat atrophy. These sites then release insulin poorly. Rotating the sites prevents these problems. Hypogly-caemia may result from having too much insulin and not eating enough, or exercising. If a patient is not eating, e.g. with vomiting due to gastroenteritis, then insulin treatment should not be omitted, as the body still requires insulin to utilise glucose. Instead, lower amounts should be used with careful monitoring, or the patient will need to be admitted for intravenous glucose and insulin to avoid either diabetic ketoacidosis or hyperos-molar non-ketotic coma.