Kinetics of subcutaneous NPH insulin in diabetics

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Abstract
Kinetics of s.c. NPH insulin were studied in newly diagnosed insulin-dependent diabetics. Using a biotelemetric technique with small Geiger-Mueller detectors applied to the skin surface, the disappearance of 125I-NPH insulin from subcutis was monoexponential, with a mean half-life of 6.6 .+-. 3.3 h. A model is presented to compare the disappearance rates of s.c. 125I-NPH insulin and the calculated plasma appearance insulin curve derived from the actual plasma insulin concentration measurements, assuming a 1-compartment model and 1st-order kinetics. Areas under the absorption- and appearance-time curves calculated from external measurements and from plasma insulin concentrations were identical. There was a strong correlation between plasma concentrations and absorbed amounts of labeled insulin (r = 0.8782, P < 0.001), as well as between the blood glucose-lowering effects and percent absorbed insulin per hour (r = 0.7659, P < 0.001). Evidently, the disappearance rate of 125I-insulin was a relevant biological expression of insulin absorption from subcutis and a reliable noninvasive method of quantitative determination of insulin concentration in blood.