Pharmacokinetics of continuous subcutaneous insulin infusion
(1) Steno Memorial Hospital and Hagedorn Research Laboratory, Gentofte, Denmark
Received: 17 August 1982 Revised: 10 December 1982
Summary One of the reasons for the variability of blood glucose regulation
in Type 1 (insulin-dependent) diabetic patients is the huge variation in
subcutaneous absorption of intermediate-acting insulin. We have investigated
the variation in insulin absorption during continuous subcutaneous insulin
infusion in eight such patients. The content of insulin in the subcutaneous
tissue was measured using 125I-labelled insulin. The concentration of free
serum insulin and blood glucose was followed from 1 h before and from 7
h after breakfast on two consecutive days. The amount of insulin absorbed
during 24 h differed in all cases by less than 3% from the daily insulin
dose given by the pumps. Mean insulin absorption rates and mean free insulin
concentration showed peak values 30–90 min after meal bolus injections; this
was sufficient to maintain near-normal blood glucose. Mean free serum insulin
correlated strongly with disappearance of insulin from the subcutaneous
tissue (r=0.98). From the insulin absorption rates and free insulin concentrations
during basal constant insulin infusion, the half-time of serum insulin was
calculated as 6 min. Compared with the known large variability in the absorption
of intermediate-acting insulin, continuous subcutaneous insulin infusion
offers a precise and reproducible way of insulin administration resulting
in post-prandial serum insulin peaks sufficient to maintain near-normal
blood glucose levels. The half-time of serum insulin during subcutaneous
infusion corresponds to values for intravenous infusion given in the literature,
indicating that local degradation of insulin in subcutaneous tissue is of
minor importance.
Key words Continuous subcutaneous insulin infusion - insulin absorption - half-time of insulin - local insulin degradation