We recruited ten healthy volunteers (age 40 [19–61] years, mean [range]; BMI 22.5 [19.2–24.9] kg/m2) to this open-label study that used five euglycaemic glucose clamps (Biostator, mtb Medizintechnik, Ulm, Germany) with blood glucose value 5 mmol/l and basal i.v. insulin infusion 0.15 mU kg−1 min−1 administered at 2 h before until 8 h after glucose dose. The ethics committee of North Rhine in Germany approved this Good Clinical Practice study. Using a crossover study design with a fixed treatment order, 12 IU human soluble insulin (Humulin R; Eli Lilly, Indianapolis, IN, USA), 12 U insulin lispro (Humalog; Eli Lilly) and 12 IU of ultra-fast insulin (VIAject; Biodel) were injected s.c. into the abdominal wall on three study days. On two additional study days 6 and 3 IU of the ultra-fast insulin were studied. This insulin was a re-constituted, lyophilised regular human insulin. In this two-part formulation, the insulin and diluent can be shipped and stored without refrigeration. It is stable at room temperature and for at least two years when refrigerated and frozen. Re-constitution consists of withdrawing 10 ml of diluents with a syringe and injecting it into the vial containing the lyophilised insulin. Reconstitution yields a single, liquid 10 ml vial (25 IU/ml) and in liquid form it should be refrigerated.
Glucose infusion rates (GIR) as determined by the glucose clamp technique were the primary variable for analysis. Sixth-order polynomial functions were fitted to the individual baseline-corrected GIR profiles to determine the following pharmacodynamic summary measures: (1) maximum GIR (GIRmax); (2) time to GIRmax (tGIRmax); (3) time to early/late half-maximal GIRmax (tGIRmax + 50% and tGIRmax − 50%); and (4) AUCGIR for specified time intervals.
The secondary variable was the serum insulin concentration profile. From the insulin concentration over time data the following pharmacokinetic variables were derived: (1) maximum insulin concentration (C
max); (2) time to C
max (tC
max); (3) time to 50% of C
max (tC
max+50%); (4) time to 50% of C
max after C
max (tC
max−50%); and (5) the AUC of insulin concentrations (AUCINS) for specified time intervals. Human insulin serum concentrations (after administration of human soluble insulin and ultra-fast insulin) were measured by means of a commercial chemoluminescence assay (catalogue number 2-001; MLT-Research, Cardiff, UK). The assay sensitivity was 0.25 μU/ml. Insulin lispro serum concentrations were measured by means of a lispro-specific commercial RIA kit (catalogue number LPI-16K; Linco Research, St Charles, MO, USA). Analyses were performed by IKFE, Mainz, Germany. Pharmacokinetic variables were calculated directly from the assayed values. Since the assay employed for ultra-fast insulin and human soluble insulin measured endogenous insulin and the insulin administered at the glucose clamp procedure, the measured levels were adjusted for baseline and any values less than zero were set to zero. The respective pharmacokinetic variables were calculated from the adjusted data as follows: C
max and tC
max were reported from the observed adjusted maximum values, the early and late tC
max50% were calculated by linear interpolation between the two closest time points, and the AUC values were calculated using the linear trapezoidal rule. As insulin lispro and ultra-fast insulin/human soluble insulin were measured by different assays, no statistical analysis of concentration-dependent variables was made.
Differences in pharmacokinetic and pharmacodynamic variables were analysed (SAS version 8.02; SAS, Cary, NC, USA) using one-way ANOVA followed by a two-tailed Duncan’s multiple range test if the ANOVA showed significance.