Use of a novel double-antibody technique to describe the pharmacokinetics of rapid-acting insulin analogs.

OBJECTIVE To measure the contribution of bedtime intermediate-acting human insulin on the morning plasma insulin profiles after injection of the rapid-acting insulin analogs lispro and aspart in patients with type 1 diabetes. RESEARCH DESIGN AND METHODS A total of 14 patients with type 1 diabetes, aged 35 +/- 13 years (mean +/- SD), participated in this single-blind, randomized crossover study. After taking their usual injection of human intermediate-acting insulin the night before, they were given insulin aspart or insulin lispro (10 units) before a standardized breakfast. The contribution of continuing absorption of the human insulin was measured using a monoclonal antibody not cross-reacting with insulin aspart or lispro, whereas the contribution of the analogs was estimated by subtraction after measurement of all plasma free insulin using an antibody cross-reacting equally with human insulin and both analogs. RESULTS The correlation coefficient of the fasting free insulin concentrations measured with both insulin methods was 0.95. Fasting free insulin was 95 +/- 25 pmol/l before administration of insulin aspart, when determined with enzyme-linked immunosorbent assay detecting only human insulin, and 71 +/- 20 pmol/l before administration of insulin lispro (NS). Both insulin analogs gave marked peaks of free insulin concentrations, lispro at 40 +/- 3 min and aspart at 55 +/- 6 min after injection (P = 0.01). The later part of the profiles, from 4.5 to 5.5 h after injection, were similar and showed almost no contribution of the insulin analogs. CONCLUSIONS The combination of insulin assays that detect human insulin only or both human insulin and analogs provides a new tool for studying insulin pharmacokinetics. Using this technique, we showed that 4.5 h after administration of the rapid-acting insulin analogs lispro and aspart, the free insulin levels are almost only attributable to the intermediate-acting insulin given at bedtime.