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Emerging Treatments
O R I G I N A L
and Technologies
A R T I C L E
Variability of the Metabolic Effect of
Soluble Insulin and the Rapid-Acting
Insulin Analog Insulin Aspart
LUTZ HEINEMANN, PHD
CHRISTIAN WEYER, MD
MARTIN RAUHAUS, MD
SEBASTIAN HEINRICHS, MD
TIM HEISE, MD
OBJECTIVE — To study the intra- and interindividual variability of the metabolic activity of
soluble insulin and of the rapid-acting insulin analog insulin aspart after subcutaneous injection.
RESEARCH DESIGN AND METHODS — A total of nine healthy male volunteers
received subcutaneous injections of soluble insulin (0.2 U/kg) in the abdominal region on each
of the four study days. Another 10 volunteers received an injection of insulin aspart four times.
Glucose infusion rates necessary to neutralize the blood glucose–lowering effect of the administered insulin were registered during euglycemic glucose clamps (blood glucose 5.0 mmol/l;
basal intraveneous insulin infusion 0.15 mU kg 1 min 1) over the subsequent 600 min. We
investigated the variation in metabolic activity by calculating coefficients of variation (CVs).
RESULTS — In comparison to soluble insulin, subcutaneous injections of insulin aspart led
to a more rapid onset of action and a shorter duration of action. Subcutaneous injection of the
insulin preparations resulted in intraindividual CVs of the summary measures between 10 and
30% (soluble insulin vs. insulin aspart: maximal metabolic activity 15 ± 7 vs. 16 ± 10%, time
to maximal metabolic activity 14 ± 10 vs. 11 ± 6%; NS between the preparations [means ± SD]).
The decline to half-maximal activity after maximal activity showed a lower intraindividual CV
with insulin aspart (19 ± 9 vs. 11 ± 5%; P = 0.018). The interindividual CVs were higher than
the intraindividual CVs (26 vs. 28, 23 vs. 19, and 26 vs. 17%). Generally, the pharmacodynamic
variability was higher than the pharmacokinetic variability. For the pharmacokinetic measures,
the intra- and interindividual variability in tmax was lower for insulin aspart than for soluble
insulin.
CONCLUSIONS — The metabolic effect of soluble insulin shows an intraindividual variability of 10–20% in healthy volunteers, even under strictly controlled experimental conditions.
The overall variability of action of insulin aspart was comparable to that of soluble insulin.
Diabetes Care 21:1910–1914, 1998
t is daily clinical experience that subcutaneous injection of insulin leads to a
highly variable metabolic effect. This
variability hampers the strive for optimal
metabolic control. The first quantitative
estimation of the variability of insulin
I
absorption was performed in 1959 (1).
This study, as in most other studies performed later on this topic, did not investigate the variability of insulin action, but did
investigate the variability of insulin absorption from the subcutaneous depot (2–7).
From the Department of Metabolic Diseases and Nutrition, WHO Collaborating Centre for Diabetes, Heinrich-Heine University, Düsseldorf, Germany.
Address correspondence and reprint requests to Dr. Lutz Heinemann, Department of Metabolic Diseases
and Nutrition, Heinrich-Heine University Düsseldorf, P.O. Box 101007, 40001 Düsseldorf, Germany. E-mail:
[email protected]
Received for publication 15 April 1998 and accepted in revised form 17 September 1998.
L.H. is a member of an advisory panel for Novo Nordisk.
Abbreviations: AUC, area under the curve; CV, coefficient of variation; GIR, glucose infusion rate; GIRmax,
maximal glucose infusion rate; Cmax, maximal serum insulin concentration; tmax, time to GIRmax.
A table elsewhere in this issue shows conventional and Système International (SI) units and conversion
factors for many substances.
1910
For clinical purposes, quantitative data
about the intraindividual variability of the
metabolic effect of subcutaneous injected
insulin should be helpful. To quantify the
intraindividual variability of the metabolic
effect, the euglycemic clamp technique was
used in two studies (8,9). In the study by
Galloway et al. (8), the metabolic effect of
long-acting zinc insulin was investigated.
Ziel et al. (9) studied soluble insulin, but on
two study days and with a study duration
of 360 min only. Thus to date, knowledge
about the variability of the metabolic effect
of currently available short-acting insulin
preparations is limited.
Subcutaneous injection of rapid-acting
insulin analogs like insulin aspart and
insulin lispro may lead to a reduced variability of insulin action due to the weaker
self-association tendency of insulin
monomers into hexamers (10). Insulin
aspart was shown to have a more rapid onset
of action and a shorter duration of action
after subcutaneous injection than soluble
insulin (11,12). In clinical experiments, the
use of insulin lispro was reported to result in
a reduced variability of the metabolic effect
(13). Nevertheless, it has not been investigated under controlled experimental conditions, so far, if the variability of the metabolic
effect of rapid-acting insulin analogs is lower
than that of soluble insulin. We studied the
variability of insulin action and of insulin
absorption after injecting identical doses of
soluble insulin or insulin aspart subcutaneously into the abdominal region of healthy
volunteers on four study days.
RESEARCH DESIGN AND
METHODS
Subjects
A total of 20 healthy male volunteers (age
26 ± 1 [range 23–28] years; BMI 22.8 ± 1.9
[18.9–26.0] kg/m2) participated in this
double-blind study. After receiving detailed
oral and written information, all volunteers
undersigned an informed consent. The
study was performed according to the principles of Good Clinical Practice and the
declaration of Helsinki and was approved
by the local ethical committee.
DIABETES CARE, VOLUME 21, NUMBER 11, NOVEMBER 1998
Heinemann and Associates
Study protocol
During the morning of each of the four
study days, the volunteers were connected
to a Biostator after having fasted for at least
12 h. Blood glucose was kept constant at a
target level of 5.0 mmol/l by means of the
euglycemic glucose clamp technique (14).
A low-dose basal intravenous insulin infusion of 0.15 mU kg 1 min 1 was maintained continuously throughout the whole
experiment in order to establish comparable baseline insulin levels on all study days.
Baseline glucose requirements were registered for 90 min, before insulin was
injected subcutaneously by means of a
syringe (0.3-ml Microfine IV , Becton
Dickinson, Heidelberg, Germany; needle
length 13 mm) into the abdominal region.
Glucose infusion rates (GIR) necessary to
keep blood glucose constant were registered during the subsequent 600 min. The
four study days were separated by at least 7
days. The volunteers were instructed to
keep their body weight constant and to
abstain from strenuous physical exercise
during the study period.
Identical insulin doses of 0.2 U/kg body
weight (14.4 ± 1.6 [range 12–17] U) were
injected each time with the same injection
technique in the umbilical region by the
same investigator (L.H.). The needle was
inserted at a 45° angle into a lifted skinfold
in order to ensure subcutaneous injection.
Nine volunteers received subcutaneous
injection of soluble insulin on each of the
four study days (Actrapid HM, U100, Novo
Nordisk, Bagsvaerd, Denmark), whereas 10
other volunteers received injections of
insulin aspart (B28Asp; U100, Novo
Nordisk). The 10th volunteer of the soluble
insulin group developed an acute otitis
media before the first study day, which had
to be treated with antibiotics and led to this
subject dropping out of the study. The two
groups of volunteers did not differ with
respect to age and BMI.
Blood samples for estimation of plasma
glucose, serum insulin, and serum C-peptide
concentrations were collected in 30-min
intervals before the injection, and thereafter
in intervals of 10 min (0–60 min after injection), 15 min (60–120 min), and 30 min
(120–600 min), respectively. Serum insulin
and serum C-peptide concentrations were
estimated by commercial radioimmunoassays (Pharmacia Insulin RIA 100, Pharmacia
Uppsala, Sweden, intra-assay coefficient of
variation [CV] 4.9% and interassay CV
4.9%) and an enzyme-linked immunosorbent assay (ELISA) (DAKO C-peptide,
DAKO Diagnostics, Cambridgeshire, U.K.;
intra-assay CV 6.4% and interassay CV
8.7%) by Medi-Lab, Copenhagen, Denmark.
The Pharmacia Insulin RIA 100 does not
measure the concentration of insulin aspart
proportionally to human insulin concentrations. Therefore, the following corrections
formula was used to calculate the correct
insulin aspart concentrations in the blood:
Insulin aspartcorrected
F
1,503
1,398
insulin aspart (fraction)
insulin aspart (fraction)
with F denoting the dilution factor.
Statistical methods
A lognormal function was fitted to each of
the individual time-action profiles registered (15). This function allowed calculation of the following pharmacodynamic
summary measures: maximal glucose infusion rate (GIRmax), time to GIRmax (tmax’),
time to half-maximal GIR values before and
after GIRmax (early t50% and late t50%), and the
area under the curve (AUC) of GIR time
profiles. The coefficient of variation (CV =
SD / –x) was calculated for the summary
measures in order to describe the intra- and
interindividual variability of insulin action.
Intraindividual CVs were calculated from
the results obtained with each volunteer on
the four study days. Interindividual CVs
were calculated from the individual mean
values of all volunteers with an identical
insulin preparation. An unpaired, two-sided
t test was used for statistical comparison of
the intraindividual CV of the summary
measures obtained with the two insulin
preparations. A P value 0.05 was used as
significance level. To describe the individual
variability of the summary measures graphically, the individual means and their SDs
were presented (16).
Variability of insulin absorption was
studied by fitting a polynomial function to
the individual serum insulin concentration
profiles. The following pharmacokinetic
summary measures were estimated graphically: maximal serum insulin concentration
(Cmax), time to Cmax (tmax). The AUCs were
calculated for different time periods under
the individual serum insulin profiles. The
variability of these pharmacokinetic summary measures was studied as described for
the pharmacodynamic parameters.
The sample size assessment was based
on the intrasubject variation comparison.
With 20 subjects and four replications per
DIABETES CARE, VOLUME 21, NUMBER 11, NOVEMBER 1998
subject, a true ratio of SDs of 0.5 and
2.0 would be discovered with 96% probability at a 5% significance level.
RESULTS
Blood glucose
Blood glucose concentrations were kept
constant throughout the glucose clamp
experiments at identical levels (soluble
insulin vs. insulin aspart 5.0 ± 0.3 vs. 5.0 ±
0.2 mmol/l).
Time-action profile
Baseline glucose infusion rates were 1.0 ±
0.5 mg kg 1 min 1 with soluble insulin
and 0.9 ± 0.5 mg kg 1 min 1 with
insulin aspart (NS). As shown previously,
the time-action profile of soluble insulin is
characterized by a later onset of action, a
later maximal effect, and later decline back
to baseline values in comparison to the
metabolic effects registered after subcutaneous injection of insulin aspart (P 0.01;
Fig. 1A, Table 1). The maximal metabolic
effect registered was not different after subcutaneous injection of soluble insulin and
insulin aspart. Injection of insulin aspart
resulted in a higher AUC under the GIR
profiles in the first 2 h after injection (P
0.001). The overall metabolic effect over 10
h was comparable (Table 1).
The intraindividual variability of the
summary measures of soluble insulin and
insulin aspart were not significantly different
(Table 1), only the decline to half-maximal
activity after maximal activity showed a
lower intraindividual variability with insulin
aspart in comparison to soluble insulin. The
interindividual CVs were 5–20% higher
than the intraindividual ones (Table 1). The
intra- and interindividual variability of some
summary measures are given in Fig. 2A–E in
a special presentation form. Summary measures do not provide information about the
variability of insulin action over time after
insulin injection. Calculation of the mean
intraindividual CV for each of the two
insulin preparations showed that the CV
was 25% for both preparations between
60 and 360 min after injection (Fig. 2F).
Serum insulin profiles
Baseline serum insulin levels were 61 ± 11
pmol/l with soluble insulin and 55 ± 8
pmol/l with insulin aspart (NS). Serum
insulin concentrations after subcutaneous
injection of insulin aspart increased more
rapidly and to higher concentrations in
comparison with those obtained with solu1911
Variability of insulin action
ble insulin (P 0.001; Fig. 1B; Table 1).
The AUCs under the serum insulin profile
were higher during the first 2 h after injection of insulin aspart (P 0.001); however,
the AUCs were comparable over the whole
study duration.
With insulin aspart, the intraindividual
variability of tmax as well as the interindividual CVs for Cmax, tmax, and AUC0–120
were lower than with soluble insulin. The
intra- and interindividual variability for the
AUCs were lower for the pharmacokinetic
parameters in comparison to the pharmacodynamic summary measures.
Serum C-peptide levels were 0.25 ±
0.06 nmol/l after injection of regular insulin
and 0.27 ± 0.10 nmol/l with insulin aspart
(NS). Endogenous insulin secretion was
lowered to 63 ± 20% of basal levels with
regular insulin and to 66 ± 29% with
insulin aspart (NS).
CONCLUSIONS — This is the first
investigation looking at the variability of
insulin action with a fourfold administration of insulin and an observation period
covering the whole duration of insulin
action. Repeated subcutaneous injection of
soluble insulin in identical doses resulted in
an intraindividual variability of the elicited
metabolic effect between 10 and 30% and
Figure 1—Glucose infusion ratesA)
( and serum insulin concentrations
B) (after subcutaneous injecan ininterindividual variability between 20
tion of 0.2 U/kg body weight of the rapid-acting insulin analog, insulin aspart, or of soluble insulin
and 50%. Comparison of both insulin
healthy male volunteers on four study days (mean ± SEM).
Table 1—Intra- and interindividual variability of the metabolic effect and the serum insulin concentrations after subcutaneous injection of
soluble insulin or insulin aspart
Soluble insulin (n = 9)
Intraindividual Interindividual
Mean ± SD
CV (%)
CV (%)
Parameter
Pharmacodynamic
summary measures
GIRmax (mg kg 1 min
tmax (min)
Early t50% (min)
Late t50% (min)
AUC
0–120 min (mg kg 1
0–600 min (mg kg 1
Pharmacokinetic
summary measures
Cmax (pmol/l)
tmax (min)
AUC
0–120 min (nmol l 1
0–600 min (nmol l 1
1)
[120 min] 1)
[600 min] 1)
[120 min] 1)
[600 min] 1)
Insulin aspart (n = 10)
Intraindividual Interindividual
Mean ± SD
CV (%)
CV (%)
9.5 ± 2.3
156 ± 29
61 ± 12
387 ± 68
15 ± 7
14 ± 10
16 ± 10
19 ± 9
26
23
25
26
11.2 ± 2.8
104 ± 16
41 ± 8
264 ± 34
16 ± 10
11 ± 6
16 ± 9
11 ± 5*
28
19†
25†
17†
533 ± 216
3,011 ± 548
27 ± 22
13 ± 3
44
21
861 ± 270
2,840 ± 566
21 ± 12
18 ± 13
36†
25
195 ± 41
129 ± 36
19 ± 8
24 ± 10
28
37
341 ± 40
70 ± 9
14 ± 9
15 ± 6*
18†
20†
16.1 ± 2.9
52.9 ± 5.9
19 ± 8
14 ± 10
31
17
30.8 ± 3.2
52.3 ± 7.2
16 ± 8
15 ± 7
18†
19
The summary measures were estimated after subtraction of baseline glucose infusion rates and serum insulin concentrations. *P
0.001 vs. soluble insulin.
1912
0.05 vs. soluble insulin; †P
DIABETES CARE, VOLUME 21, NUMBER 11, N OVEMBER 1998
Heinemann and Associates
Figure 2—To describe the intraindividual and the interindividual variability seen with different summary measures
A–E), the
( SD of the four measur
ements with each volunteer in relation to the mean value are plotted. The SD of the mean value of all individual mean
(—
values
) describe the interindiIn the mean intraindividual coefficient of variation
vidual variability, whereas the SD of all the individual SDs
( ) describe the intraindividual variability. F,
of the glucose infusion rates over time with the two insulin preparation are given.
preparations studied revealed that the variability of action of insulin aspart was comparable to that of soluble insulin for most
summary measures.
There are two possible explanations for
the variability of insulin action: 1) pharmacokinetic variability (i.e., same doses of
insulin lead to different plasma insulin concentrations), and 2) pharmacodynamic variability (i.e., similar plasma insulin
concentrations induce different metabolic
effects). Concerning the variability of insulin
absorption (the pharmacokinetic part), a
number of studies have been performed
using radioactively labeled soluble insulin
(1–7). With this semiquantitative method,
an intraindividual CV of 15% and an
interindividual CV of 30% has been estimated for the time to decline to half-maximal radioactivity over the insulin depot in
the skin (T50%) for soluble insulin (7). Direct
measurement of the serum insulin concentrations after subcutaneous insulin injection revealed a considerably higher
intraindividual variability of Cmax and tmax of
64 and 107% (soluble insulin), 28 and 34%
DIABETES CARE, VOLUME 21, NUMBER 11, NOVEMBER 1998
(lente insulin), and 44 and 68% (NPHinsulin) (17). Insulin absorption from the
subcutaneous depot might also vary from
injection site to injection site caused by the
anatomical properties (e.g., local blood
flow) and/or the local degradation of insulin
(6,18,19). Injection of human insulin into
the abdominal region resulted in a lower
variability than that observed after injection
of the respective porcine insulin preparation
in the deltoid region (8).
The variability of insulin action (the
pharmacodynamic part) was studied quan1913
Variability of insulin action
titatively with the euglycemic glucose
clamp technique in two studies only (8,9).
Galloway et al. (8) found intra- and
interindividual CVs between 35 and 55%
for the calculated summary measures for
slow-acting insulin preparations employing
an unbalanced study design with eight
healthy volunteers. Ziel et al. (9) studied
the variability of insulin absorption and
insulin action with soluble insulin employing a similar study protocol as in our study,
but with two study days and a study duration of 360 min only. In this study, the
intraindividual CV for the total AUC below
the insulin profile was 11%, which was
lower than the CV for the AUC below the
time-action profile (23%). Also in our
study, the variability of the pharmacokinetic summary measures was lower than
that of the pharmacodynamic parameters.
It is reasonable to assume, that in daily
life the variability of insulin action in diabetic patients is even higher than that
observed in healthy volunteers studied
under controlled experimental conditions.
Factors like insulin antibodies, changes in
metabolic control, or previous hypoglycemic episodes with their impact on the
actual insulin sensitivity were ruled out by
our study design. The high variability of the
metabolic response to application of identical insulin doses is a serious problem for
insulin-treated diabetic patients and hamper the achievement of a good metabolic
control without suffering from hypoglycemic events. The poor reproducibility of
the metabolic effects of subcutaneous
insulin therapy might be a source of frustration and uncertainty in many patients.
Therefore, development of insulin preparations with a lower variability of action
remains an important task for the future.
From a clinical study with insulin lispro it
was anticipated that the more rapid absorption of the insulin analog might result in a
lower variability of insulin absorption and
probably also insulin action in comparison
to soluble insulin (13). Nevertheless, we
did not observe a lower variability of
insulin action after subcutaneous injection
1914
of insulin aspart under controlled experimental conditions, with the exception of
the decline of the metabolic effect induced.
In summary, under experimental conditions in healthy volunteers, subcutaneous
injection of soluble insulin resulted in an
intra- and interindividual variability in
insulin action of 30%. The variability of
action of insulin aspart was equivalent to
that of soluble insulin.
9.
10.
Acknowledgments — We gratefully acknowledge the skillful help of C. Gottschalk, A.
Brodeßer, and M. Schreier during this study. We
thank Dr. R. Bender for fitting the lognormal
functions to the GIR curves and for the calculation of the summary measures. We thank Novo
Nordisk, Mainz, Germany, and Copenhagen,
Denmark, for their support during the study.
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