Absorption of isophane (NPH) insulin and its clinical implications

Abstract

Absorption of 125I-NPH insulin (125I-isophane insulin) (40 IU/ml) was studied in eight diabetics given 50% and 150% of their normal daily dose of insulin. Insulin absorption correlated with plasma insulin (r = 0.97, p < 0.001) and blood glucose (r = -0.87, p < 0.01) concentrations. Absorption was slower at higher doses, so that trebling the insulin dose only doubled the amount absorbed over the first 24 hours. The plasma elimination half time (t 1/2 ) of insulin was about five minutes. Thus, the disappearance of radiolabelled insulin is a reliable and quantitative index of insulin absorption; subcutaneous degradation, if present, is minimal and constant. Changes in dose of intermediate-acting insulin further increases the large variation in insulin absorption. This implies that minor adjustments of intermediate insulin dosage are probably futile.