The total daily output of endogenous insulin from pancreatic islet cells is 30-40 units (determined by the needs of completely pancreatectomised patients), and most insulin-deficient diabetics will need 30-50 unit/day (0.5-0.8 units/kg) of insulin (two-thirds in the morning and one-third in the evening).
Initial treatment for a Type 1 (IDDM) patient, who does not present with ketoacidosis, will usually be outside hospital with two injections of intermediate-acting insulin, or a mixed insulin. Other permutations, including soluble insulin before each meal, and an intermediate-acting insulin at bedtime, can follow later. The following is a guide to initial daily dose requirements:
The dose is adjusted according to the usual monitoring of blood5 glucose (or urine, if glucose meters are unavailable). Daily (total) dose increments should be 4 units at 3-4-day intervals.
If it is decided to give the patient only one injection per day, then 10-14 units of an intermediate-acting isophane suspension may be given. Dose increments (4 units) may be made on alternate days. Soluble insulin (neutral) may be added, or mixed (biphasic) insulins may be used, according to the patient's response.
When stable, patients usually receive either a biphasic insulin or a mixture of soluble, short-acting human insulin, and a longer-acting suspension of insulin with protamine or zinc.
Excessive dose of insulin leads to overeating and obesity; it also leads to hypoglycaemia (especially nocturnal), that may be followed by rebound morning hyperglycaemia that is mistakenly treated by increased insulin, thus establishing a vicious cycle (Somogyi effect).
Physical activity increases carbohydrate utilisation and insulin sensitivity, so that hypoglycaemia is likely if a well-stabilised patient changes suddenly from an inactive existence to a vigorous life. If this is likely to happen the carbohydrate in the diet may be increased and/or the dose of insulin reduced by up to one-third and then readjusted according to need. This is less marked in patients on oral agents.
See also Selection of therapy and Ketoacidosis (below).
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