Clinical Pharmacology of
`Human Insulin
`
`Lirrz HEINEMANN, PHD
`BERND RICHTER, MD
`
`Nowadays, human insulin is used daily by millions of diabetic patients. The biolog-
`ical effect of human insulin is comparable to that of porcine insulin. However, after
`subcutaneous injection, pharmacological and clinical studies showed pharmacoki-
`netic and pharmacodynamic differences between human and animal insulins. Human
`insulin tends to have faster absorption and shorter duration of action compared with
`animal insulin. These differences are more pronounced and can be of clinical
`relevance with intermediate- and long-acting insulin preparations. Optimal meta-
`bolic control can be achieved with either human or highly purified animal insulin
`preparations, provided appropriate insulin replacement strategies are used.
`
`T he development of manufacturing
`
`techniques for human insulin has
`made it possible to treat IDDM pa-
`tients with a hormone that has an amino
`acid sequence identical to endogenous
`insulin. After characterization of the bi-
`ological activity of human insulin in vitro
`and in animal studies, a series of efficacy
`and safety trials with human insulin in
`humans was performed (1,2). In the first
`years, several studies compared the po-
`tency of human insulin and animal insu-
`lin preparations with regard to their
`pharmacological properties. Later, such
`studies were performed to compare hu-
`man insulin preparations manufactured
`using different methods (3,4).
`It is surprising how much of the
`literature on human insulin, including
`proceedings of commercially sponsored
`symposia as well as papers and reports
`
`published in books and supplements to
`well-known journals, was printed 10
`years ago, all non-peer-reviewed, com-
`pared with the number of original papers
`published on human insulin that have
`passed a peer-review system. This is dis-
`turbing, because pharmacological differ-
`ences between human insulin and ani-
`mal insulin might have practical
`implications for the daily therapy of mil-
`lions of patients.
`In this paper, we will review the
`properties of human insulin preparations
`available today for clinical practice. Fur-
`thermore, we will describe the pharma-
`cological differences between human insu-
`lin and highly purified (monocomponent)
`insulin preparations of animal origin. We
`attempt to give a balanced overview of the
`results of all studies, comparing various
`pharmacological aspects of human insulin
`
`From the Department of Nutrition and Metabolic Diseases (WHO Collaborating Center for
`Diabetes), Heinrich-Heine-Universiry of Diisseldorf, Dusseldorf, Germany.
`Address correspondence and reprint requests to Lutz Heinemann, PhD, Department of
`Nutrition and Metabolic Diseases, Heinrich-Heine-University of Dusseldorf, P.O. Box 10 10
`07, Moorenstr. 5, 40001 Dusseldorf, Germany.
`IDDM, insulin-dependent diabetes mellitus; N1DDM, non-insulin-dependent diabetes mel-
`litus.
`
`and animal insulin. As a result, it was nec-
`essary to quote papers that were not peer-
`reviewed.
`A major emphasis of this review
`is the presentation of the time-action
`profiles of the most widely used human
`insulin preparations. A mere discussion
`of differences between human insulin
`and animal insulins would be somewhat
`out of date, because, in many countries,
`human insulin is already used by most
`patients.
`
`STRUCTURE, PRODUCTION,
`PURITY, AND POTENCY OF
`HUMAN INSULIN
`
`Structure
`The structure of animal insulin has mi-
`nor but potentially important differences
`from human insulin: Porcine insulin dif-
`fers by one amino acid (alanine instead
`of threonine at the carboxy-terminal of
`the B-chain, i.e., position B30), and beef
`insulin differs by two additional alter-
`ations of the sequence of the A-chain
`(threonine and isoleucine on positions
`A8 and A10 are alanine and valine).
`Thus, there is nearly a complete homol-
`ogy between human insulin and porcine
`insulin in the amino acid sequence.
`None of the differences between
`human insulin and animal insulins is
`thought to be at sites crucial to the bind-
`ing or action of insulin. Therefore, it
`could be expected that the receptor bind-
`ing and cellular interactions of human
`insulin would not differ significantly
`from those of pork or beef insulin (2).
`The amino acid on position B30 is near
`one of the parts of the insulin molecule
`thought to be involved in the self-
`association of two insulin molecules into
`dimers. Thus, the self-association ten-
`dency could be different between human
`insulin and porcine insulin (5).
`The physicochemical properties
`of human, pork, and beef insulins differ
`somewhat because of their different
`amino acid sequence. Threonine adds
`
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`Heinemann and Richter
`
`one extra hydroxyl group to the human
`insulin molecule. This increases its hy-
`drophilic properties and decreases the
`lipophilic properties, as compared with
`that of porcine insulin. Thus, the solu-
`bility of human insulin in aqueous solu-
`tions is higher than that of porcine insu-
`lin.
`
`Production
`One way to mass produce human insulin
`was to exchange alanine in position B30
`of porcine insulin with threonine, using
`an enzymatic-chemical method (semi-
`synthetic technique) (6). During the last
`decades, biosynthetic production of hu-
`man insulin was made possible through
`advances in genetic engineering, espe-
`cially in recombinant DNA technology
`(7,8). Methods used to produce human
`insulin have changed considerably dur-
`ing the last decade. At the end of the
`1980s, the semi-synthetic production of
`human insulin was essentially stopped
`and replaced by biosynthetic production.
`In the beginning of the biosynthetic pro-
`duction of human insulin, the A and B
`chains were produced separately and had
`to be combined. At present, biosynthetic
`human insulin is produced with a perfect
`three-dimensional structure; that is, all
`foldings and disulfide bridges of the in-
`sulin precursor produced by the bacteria
`or yeast cells are identical to endogenous
`insulin. The correct spherical structure is
`important for the insulin-insulin recep-
`tor interaction, and hence for the biolog-
`ical action of insulin. Porcine insulin has
`a slightly different
`three-dimensional
`structure when compared with human
`insulin (9).
`
`Purity
`To ascertain a low immunogenicity of
`human insulin preparations, impurities
`had to be avoided. The semi-synthetic
`human insulin production could take ad-
`vantage of the well-established produc-
`tion and purification methods for por-
`cine insulin, which was used as the
`original substrate. Possible contamina-
`tions with proinsulinlike or glucagonlike
`
`substances, pancreatic polypeptide, so-
`matostatin, and vasoactive intestinal pep-
`tides were avoided by using monocom-
`ponent porcine insulin. Contamination
`by enzymes or waste products, as a result
`of the enzymatic-chemical exchange of
`one amino acid during the secondary
`production step, also could be avoided
`(10). In contrast, the insulin production
`methods that use recombinant DNA
`technology have a higher propensity for
`contamination of the insulin product
`with various bacterial or yeast cell poly-
`peptides. The first biosynthetic human
`insulin production using bacteria had
`more obstacles in achieving purity, at-
`tributable to the fact that the A-and
`B-chains had to be extracted separately,
`and the two chains had to be combined
`with an intact insulin molecule. Thus,
`proteins and other substances of bacte-
`rial origin, as well as waste products of
`the insulin recombination, had to be
`eliminated. Later, purification methods
`were developed to obtain insulin prepa-
`rations free of any potentially harmful
`contamination by Escherichia coli- derived
`peptides (11-13). Antibodies to such
`peptides could not be detected in 10
`patients treated with human insulin for 6
`mo (12). Some of the problems of the
`recombinant DNA technique were cir-
`cumvented when it became possible to
`produce homologous proinsulin by E.
`coli (13). Thus, only the C-peptide-like
`sequence had to be cleaved to achieve
`human insulin. Human insulin produced
`biosynthetically from yeast cells with a
`different insulin precursor (not identical
`to human proinsulin) was even easier to
`clear from impurities because the precur-
`sor is secreted into the medium, and after
`cleavage of C-peptide, the intact mole-
`cule can be obtained (14,15). Because of
`the sophisticated purification
`tech-
`niques, it can be assumed that advanced
`human insulin preparations are pure and
`free of any significant contamination
`(16). In regular insulin preparations, in-
`sulin molecules self-associate to dimers
`and large oligomers. In addition, a small
`amount of covalently aggregated dimers
`
`and other insulin-transformation prod-
`ucts is formed in commercial insulin.
`These transformation products prevail in
`the blood of insulin-treated diabetic pa-
`tients because they have a slower meta-
`bolic clearance relative to insulin mono-
`mers (17-19). Human insulin was
`reported as more susceptible to the pro-
`duction of such products than beef insu-
`lin (19). These transformation products
`are claimed to be highly immunogenic.
`In addition, degradation of the injected
`insulin occurs in the subcutaneous de-
`pot, resulting in degradation products
`that also might have immunogenic activ-
`ity (20).
`It has to be emphasized that even
`with a hormone identical to the human
`insulin, there are still major differences
`compared with the naturally occurring
`hormone. The route of insulin adminis-
`tration is different, and the insulin prep-
`arations contain additives like antisep-
`tics, stabilizers, and, with NPH-insulins
`(Isophane), xenomorphous proteins like
`protamine.
`
`Potency
`In the first study that reports the effects
`of short-acting human insulin produced
`by recombinant DNA technology in
`healthy men, the plasma glucose decre-
`ment after subcutaneous injection of hu-
`man insulin was similar to that of highly
`purified porcine insulin (21,22). The po-
`tency of semi-synthetic human insulin or
`biosynthetic human insulin also was re-
`ported to be similar to that of animal
`insulin after intravenous insulin infusion
`at various doses or after subcutaneous
`injection in diabetic patients (2).
`In the rabbit hypoglycemia bio-
`assay, used to estimate insulin strength,
`porcine and human insulin also had a
`similar potency (11,23). However, in this
`model, human insulin showed a more
`rapid onset and a shorter duration of
`action, along with a lower potency, com-
`pared with bovine insulin (23). Most in-
`vestigators came to the conclusion that
`there is no difference in the biological
`potency of human insulin and animal
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`Pharmacology of human insulin
`
`insulins (1,2). However, this seems to
`apply only for the intravenous route and
`not for subcutaneously injected insulin.
`Differences in the absorption properties
`of human insulin and animal insulins,
`and the results of clinical studies (see
`below), led to the suggestion that the
`daily dose of insulin should be reduced
`by 10 to 25% when switching from an-
`imal insulin to human insulin (24). Such
`a dosage reduction may be needed espe-
`cially in those patients previously treated
`with bovine insulin or with mixed ani-
`mal insulins.
`The British Pharmacopoeia; Codex
`medicamentarius and the Pharmacopeia of
`the United States permit deviations from
`the declared concentration of commer-
`cial insulins of ± 5 and ± 10%, respec-
`tively. Thus, it cannot be excluded that
`some of the differences in the reported
`potencies could be attributable to varia-
`tions in insulin dose.
`
`HUMAN INSULIN
`PREPARATIONS
`Shortly after its introduction human in-
`sulin became available in short-, inter-
`mediate-, and long-acting formulations.
`In principle, these formulations are iden-
`tical to their porcine or bovine counter-
`parts with respect to the content of aux-
`iliary substances. Because most brands
`with animal insulins are still available,
`clinicians and patients are faced with a
`plethora of different insulin preparations.
`Even professionals find it difficult to
`keep track of the insulin preparations
`available in different countries, because
`various names may be used for the same
`insulin with different compositions and
`concentrations. Some of the insulin
`preparations marketed are of question-
`able usefulness, for example, mixtures of
`short- and intermediate-acting human
`insulin in 10% steps ranging from 10%:
`90% to 50%:50%. However, this com-
`ment should not be misinterpreted as a
`suggestion to withdraw animal insulin
`preparations from the market altogether.
`Some manufacturers of insulin have tried
`to withdraw animal insulins from the
`
`market (and some have actually done
`so). This is understandable from a com-
`mercial point of view (standardization of
`production). However, because human
`insulin has no clear clinical benefit, ani-
`mal insulins should stay available.
`
`PHARMACOKINETIC AND
`PHARMACODYNAMIC
`PROPERTIES OF HUMAN
`INSULIN PREPARATIONS
`
`Methods used to study the
`pharmacological properties of
`insulin preparations
`In many studies investigating insulin ab-
`sorption (pharmacokinetic studies)
`and/or insulin action (pharmacodynamic
`studies), inappropriate methods, differ-
`ent doses, and sites of administration
`have been used. This makes the compar-
`ison of the results difficult. In some stud-
`ies, the diabetic patients investigated had
`been previously treated with animal in-
`sulins. As a result, these patients might
`have had insulin antibodies, which
`might have influenced the pharmacolog-
`ical properties of exogenous insulin
`preparations. In fact, the variable disso-
`ciation rates of insulin from circulating
`antibodies are likely to contribute to the
`high variability in the bioavailability of
`any insulin preparation.
`In principle, the pharmacokinetic
`properties of insulin preparations could
`be studied using the direct method (i.e.,
`measurement of serum insulin concen-
`tration) or an indirect method (i.e., in-
`jection of radiolabeled insulin and regis-
`tration of the disappearance from the
`subcutaneous tissue). The problems and
`pitfalls that limit the use of the indirect
`method have been discussed in detail
`elsewhere (25).
`Pharmacodynamic properties can
`be studied by following the blood glu-
`cose-lowering effect of a subcutaneous
`insulin injection over time. This test of
`insulin activity results in a stimulation of
`the counterregulatory response caused
`by hypoglycemia. The effect of the coun-
`terregulatory hormones tends to increase
`
`blood glucose, thereby leading to an un-
`derestimation of the response to the in-
`jected insulin. Thus, relevant pharmaco-
`dynamic differences can only be detected
`if doses or activities of the insulins inves-
`tigated are substantially different. To
`avoid hypoglycemic episodes, blood glu-
`cose can be kept constant by an intrave-
`nous glucose infusion targeted to main-
`tain blood glucose at normoglycemic
`values (euglycemic glucose clamps). Be-
`cause the glucose requirement is propor-
`tional to the biological activity of insulin,
`it provides a direct measure of potency,
`at least with regard to glucose metabo-
`lism. Endogenous insulin secretion in
`healthy volunteer subjects can be sup-
`pressed by a low-dose intravenous insu-
`lin infusion. In our opinion, the euglyce-
`mic glucose clamp technique is the best
`method currently available to study
`pharmacodynamic properties of various
`insulin preparations. Moreover, pharma-
`cokinetic properties can be studied si-
`multaneously (2,26,27)
`A recent survey of the literature
`showed that time-action profiles of many
`insulin preparations are not well-defined
`because different methods, patient-
`selection criteria, insulin doses, methods
`of insulin administration, insulin con-
`centrations, and injection sites are used
`(28). This survey also highlights the large
`differences in the reported pharmacolog-
`ical properties of the same insulin prep-
`arations caused by the method used. For
`example, in the 22 studies analyzed, the
`onset of action after subcutaneous injec-
`tion of human regular insulin ranged
`from 0.08-0.5 h, with peak action from
`0.75-4 h, and duration of action from
`4-12 h.
`The direct comparison of phar-
`macokinetic and pharmacodynamic re-
`sults obtained with the same group of
`volunteer subjects showed a consider-
`able difference between the insulin con-
`centration-time profile and the glucose
`infusion rate-time profile. Thus, an in-
`crease in serum insulin concentration
`does not result in an instantaneous in-
`crease in glucose metabolism (Fig. 1).
`
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`A
`
`serum Insulin concentration
`
`300
`
`•120 -90 -60 -30 0 30 60 90 120 160 160 210 240 270 300 31
`
`time (mln)
`
`B
`
`glucose Infusion rates (mg/mln/kg)
`10
`
`jected 125I-labeled insulin showed a sim-
`ilar insulin absorption process of human
`and porcine insulin (31,32). However, in
`another study with the same method,
`human insulin was more rapidly ab-
`sorbed than porcine insulin (33). Ad-
`ministration of human or porcine insulin
`by intravenous bolus in healthy volun-
`teer subjects and IDDM patients showed
`that both insulins have similar biological
`activities (34). In studies with intrave-
`nous infusion of human or porcine insu-
`lin, plasma insulin concentrations and
`metabolic effects were comparable and
`strictly dose dependent (35-37). Com-
`bining intravenous insulin infusion with
`the euglycemic clamp technique showed
`that the pharmacodynamic properties of
`semi-synthetic human insulin and por-
`cine insulin were indistinguishable in
`normal individuals as well as in diabetic
`Figure 1—A: Serum insulin concentrations
`patients (26,38-40).
`during an 8-h eugtycemk glucose clamp in 8
`normal subjects. A subcutaneous injection of 12
`The appearance of human insulin
`U of regular human insulin was given at time 0,
`in plasma after subcutaneous injection
`with a WO formulation (mean + SE) on one day
`was more rapid than after a similar dose
`and a U100 formulation (mean - SE) on an-
`of porcine insulin (32,33,41-43). How-
`other day. Asterisks mark significantly different
`ever, no dose-dependent changes in
`serum insulin concentrations. *, P < 0.05; **,
`pharmacokinetic parameters could be
`P < 0.02; paired Student's t test) (55); B: Glu-
`demonstrated after a subcutaneous insu-
`cose infusion rates on the U40- (mean + SE)
`lin injection measuring blood glucose
`and on the U100- (mean — SE) insulin injection
`decline (21,44).
`day.
`Measurement of the time-action
`profile of short-acting human insulin af-
`ter its subcutaneous injection by the glu-
`cose clamp technique showed a more
`rapid onset of action and an earlier peak
`action than after injection of porcine in-
`sulin in healthy volunteer subjects as
`well as in IDDM patients (42).
`In summary, in 11 of 16 studies
`analyzed, the authors concluded that hu-
`man insulin was absorbed slightly faster
`from the subcutaneous injection site, in-
`dependent of its semi-synthetic or bio-
`synthetic origin (3,22,32,33,41-43,45-
`48). No difference in insulin absorption
`kinetics was seen in five studies
`(31,44,49-51). The mechanism of the
`faster absorption of human insulin in
`comparison to pork-regular insulin
`might be explained by the greater hydro-
`philicity of the human insulin molecule
`
`U100
`U40
`
`•120 -80 -60 -30 0 30
`
`120 150 180 210 240 270 300 330 !
`
`time (mln)
`
`This phenomenon becomes more clear in
`view of more recent studies about the
`importance of the endothelial barrier on
`insulin transport across the capillary wall
`(29,30). A long series of events is inter-
`posed between the appearance of insulin
`in blood and changes in glucose metab-
`olism. Thus, the time-dependent charac-
`teristics used to describe the pharma-
`cological characteristics of insulin
`preparations have to be different for its
`kinetic and dynamic properties.
`
`Short-acting preparations
`Pharmacological studies. Pharmacoki-
`netic properties of short-acting human
`insulin individually assessed by decline
`of radioactivity of subcutaneously in-
`
`Heinemann and Richter
`
`(9). X-ray studies of the tertiary struc-
`tures of human and porcine insulin show
`differences only at the B30 region, where
`changes in the water attraction are lo-
`cated. Another explanation for the faster
`absorption of human insulin was the in-
`fluence that the amino acid in position
`B30 has on the strength by which the
`dimers are held together within the hex-
`amer (5). The changed solvent structure
`in the B28-B30 region and alterations in
`the intermolecular contacts have a weak-
`ening effect on the hexamer stability, re-
`sulting in a greater tendency to dissociate
`with decreasing concentration of insulin
`(5,9).
`Clinical studies. In double-blind cross-
`over studies in type I diabetic patients,
`treated either conventionally or with
`subcutaneous insulin infusion, blood
`glucose control, insulin requirement,
`and number of hypoglycemic episodes
`were not substantially different between
`human insulin and porcine insulin
`(46,52,53). However, in one double-
`blind study in 21 diabetic children who
`were in poor metabolic control, signifi-
`cantly higher HbAx values were reported
`during the treatment period with human
`insulin, compared with that with porcine
`insulin (15.7 ± 2.3 vs. 14.2 ± 2.3%;
`P < 0.01) (54).
`Time-action profile and influence of
`insulin concentrations. Studies of
`short-acting human insulin in different
`concentrations (U40 vs. U100; Actrapid
`HM, Novo/Nordisk, Bagsvaerd, Den-
`mark) found the onset of action occurred
`within 15-30 min, and peak action was
`observed 150-180 min after subcutane-
`ous injection of 12 U (Fig. IB) (55). No
`significant differences were observed in
`the glucose infusion rates needed to keep
`blood glucose constant after injection of
`insulin, with either U40 or U100 con-
`centrations. However, serum insulin
`concentrations showed small but signif-
`icant differences shortly after injection
`(Fig. 1A): Serum insulin concentrations
`were significantly higher 10-20 min af-
`ter injection of the U40 formulation in
`comparison with the U100 formulation.
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`Pharmacology of human insulin
`
`However, glucose infusion rates during
`this time were not significantly different.
`In this experiment, 6 h after injection of
`a moderate dose of "short-acting" insu-
`lin, still more than 50% of maximal glu-
`cose infusion rates were needed to keep
`blood glucose concentration constant.
`Therefore, compared with the endoge-
`nous insulin response to a meal, onset of
`action and peak action occurred consid-
`erably later. In addition, duration of ac-
`tion was longer, requiring consumption
`of a snack 2 -3 h after insulin injection to
`prevent hypoglycemia. Moreover, it has
`to be emphasized that considerable devi-
`ations from the described time-action
`profile can occur depending on the sub-
`ject's insulin sensitivity (i.e., in diabetic
`patients, depending on the degree of
`metabolic control or depending on the
`insulin doses used).
`
`Clinical implications. Rapid initial de-
`livery of insulin plays a crucial role in the
`control of meal-related glycemic excur-
`sions. Thus, the more rapid onset of ac-
`tion of human insulin might have an
`advantage over short-acting animal insu-
`lins. It was shown in two studies that
`subcutaneously injected human insulin
`was superior to porcine insulin in the
`control of meal-related glycemic excur-
`sions in IDDM patients (48,56). In an-
`other study with IDDM patients, no dif-
`ferences
`in postprandial glycemic
`excursions could be demonstrated (51).
`The preprandial glucose levels were ele-
`vated in this study (>13.5 mM), and,
`therefore, prandial glycemic increases
`were small, ranging from 0-4.4 mM. In
`this context, the slightly faster absorption
`of human insulin did not result in clini-
`cally important differences.
`Obviously, the pharmacody-
`namic characteristics of human short-
`acting human insulin are far from ideal.
`In other words, the time-action profile of
`these preparations differs considerably
`from the prandial insulin requirements.
`Development of short-acting insulin an-
`alogues with a significantly faster onset
`of action might help to improve prandial
`control (5,57,58).
`
`Intermediate-acting preparations
`(NPH and lente)
`Pharmacological studies. Intermediate-
`acting human insulin preparations in-
`jected subcutaneously showed variable
`results in pharmacological studies when
`compared with their animal insulin
`counterparts. No differences in the de-
`cline of blood glucose concentrations af-
`ter injection of biosynthetic human insu-
`lin or porcine insulin could be observed
`in the first pharmacodynamic study with
`NPH insulins (44). However, NPH insu-
`lins with human insulin showed a more
`rapid onset and shorter duration of ac-
`tion than corresponding animal insulins
`in a series of later pharmacological stud-
`ies (4,27,41,59,60). In contrast to these
`results, the disappearance rates of 125I-
`labeled human or porcine NPH insulin
`preparations were not significantly dif-
`ferent when given to diabetic patients
`(32,61).
`
`The differences in the pharmaco-
`logical properties were attributed to the
`more hydrophilic properties of human
`insulin and to differences in the interac-
`tion of human insulin and animal insulin
`with protamine (41). Also, formulation
`differences, such as the nature and quan-
`tity of the protamine in the formulas
`used were implied.
`Direct comparison of semi-syn-
`thetic and biosynthetic human NPH in-
`sulin after injection in healthy volunteer
`subjects showed a similar maximal hy-
`poglycemic effect within 3 -5 h after ad-
`ministration (4). Thereafter, with semi-
`synthetic NPH insulin, plasma glucose
`remained significantly lower than with
`biosynthetic NPH insulin. These results
`suggested that the biosynthetic human
`NPH insulin had a less potent glucose-
`lowering effect and a relatively shorter
`duration of action compared with semi-
`synthetic NPH insulin.
`Comparison of human prot-
`amine-sodium insulin with human NPH
`insulin in normal subjects during a eu-
`glycemic clamp showed a slightly earlier
`peak in plasma insulin concentrations
`with the protamine sodium insulin and a
`
`longer duration of action with the NPH
`insulin (62). In a disappearance study in
`diabetic patients, human NPH insulin
`showed a decline of radioactivity similar
`to the Monotard (Monotard MC, Novo/
`Nordisk) (61). A semi-synthetic human
`insulin preparation (Monotard HM, No-
`vo/Nordisk) showed similar disappear-
`ance rates compared with a porcine lente
`preparation in 11 IDDM patients (31). In
`accordance with this, no significant dif-
`ferences were found in serum insulin
`concentrations between human and por-
`cine Monotard in short-term studies with
`healthy volunteer subjects (41,46).
`Clinical studies. In the first clinical trial
`with diabetic patients, significantly
`higher blood glucose levels were ob-
`served with human insulin before the
`morning and evening injection com-
`pared with the levels when treated with
`animal insulin. This was attributed to a
`more rapid absorption of the human
`NPH insulin (63). In a 15-mo double-
`blind crossover study, Home et al. (64)
`found a small but significant difference in
`the metabolic control between human
`and porcine insulin in 96 insulin-treated
`diabetic patients. The fasting blood glu-
`cose concentration and HbAx were sig-
`nificantly higher with human insulin
`than with porcine insulin (11.1 vs. 9.3
`mM and 11.7 vs. 11.1%, respectively). A
`short-term double-blind crossover study
`in 8 IDDM patients, comparing human
`with porcine lente insulin, resulted in no
`differences in blood glucose control (31).
`Thus, the use of human NPH in-
`sulin instead of animal NPH insulin
`could be a disadvantage. This finding
`was tested by another 6-mo double-
`blind, crossover study in 22 IDDM pa-
`tients, which resulted in similar 24-h
`blood glucose profiles, fasting blood glu-
`cose levels, HbAlc levels, number of hy-
`poglycemic events, and insulin-dose re-
`quirements when using semi-synthetic
`human NPH insulin and porcine NPH
`insulin (65). The authors discuss the
`possibility that it might be of clinical
`importance whether semi-synthetic or
`
`94
`
`DIABETES CARE, VOLUME 16, SUPPLEMENT 3, DECEMBER 1993
`
` P. 5
`
`UT Ex. 2048
`SteadyMed v. United Therapeutics
`IPR2016-00006
`
`

`
`Heinemann and Richter
`
`elevated fasting blood glucose concentra-
`tions when human NPH insulin was
`used as the evening injection led to trials
`in which the evening injection was
`moved to bedtime, or long-acting hu-
`man insulin preparations (Ultratard HM)
`were used. Fasting blood glucose con-
`centrations were significantly lower
`when the evening dose of human NPH
`insulin was given at bedtime instead of at
`dinner (7.5 ± 1.1 vs. 10.0 ± 1.6 mM;
`P < 0.02) (68). Human ultralente insu-
`lin injected at bedtime, with its longer
`duration of action, resulted in lower fast-
`ing blood glucose concentrations com-
`pared with human NPH insulin (69,70).
`In a crossover, randomized dou-
`ble-blind trial of 82 IDDM patients, the
`use of human lente (Monotard HM, No-
`vo/Nordisk) or NPH insulin, given twice
`daily in combination with regular human
`insulin, resulted in comparable meta-
`bolic control (71). With both regimens,
`the major problem was elevated blood
`glucose concentrations before breakfast
`(NPH insulin versus lente insulin:
`8.8 ± 0.5 vs. 9.0 ± 0.5 mM, NS). Thus,
`the use of human lente insulin instead of
`NPH insulin does not appear to result in
`better metabolic control during the
`night.
`
`In the above study (and others
`quoted), the diabetic patients mixed the
`regular insulin with the lente insulin im-
`mediately before the injection. It is well
`known that this procedure results in
`modifications of the time-action profile
`of regular insulin (see below).
`
`Long-acting human insulin
`preparations
`Ultralente insulin preparations made
`with bovine or porcine insulin have a
`different pharmacokinetic profile from
`those made with human insulin (72,73).
`It is known that human zinc insulin crys-
`tals bind water more avidly than pork
`insulin crystals. It may be that this causes
`a faster dissociation of those zinc insulin
`complexes (2,9). Thus, a better solubility
`of the crystals of the human insulin ul-
`tralente preparations compared with
`
`glucose Infusion rate (mg/kg/mln)
`free plasma Insulin
`
`**
`
`B
`
`glucose Infusion rate (mg/kg/min)
`free plasma Insulin
`20
`
`lnsulatard H
`
`u •
`
`- 3 - 10 1 3 5
`
`7
`
`9 11 13 15 17 19
`time (h)
`
`- 3 - 10 1 3
`
`5 7 9 11 13 15 17 19
`tims(h)
`
`glucose infusion rate (mg/kg/mln)
`5
`free plasma Insulin (pU/ml)
`
`C
`
`Protaphane HM
`
`glucose Infusion rate (mg/kg/mln)
`free plasma Insulin j/U/ml)
`
`4
`
`3 2
`
`- 3 - 10 1 3
`
`5
`
`7 9 11 13 15 17 19
`time (h)
`
`-3
`
`-1 0 1 3
`
`5 7 9 11 13 15 17 19
`time (h)
`
`Figure 2—Glucose infusion rates (\Z3), plasma free insulin (
`), and C-peptide (
`concentrations after subcutaneous injection of 12 U of 4 different human NPH insulin formulations
`(biosynthetic origin: Humulin N [A], Lilly, Indianapolis, IN; semi-synthetic origin: lnsulatard H [B]
`and protaphane HM [C], Novo/Nordisk; Basal H-lnsulin [D], Hoechst AG, Frankfurt/Main, Ger-
`many; all U40) at time 0 during 19-h euglycemic glucose clamps in 6 normal subjects. ( ^3 ), Basal
`glucose infusion rate, expressed as means + SD. *, Significantly different glucose infusion rates of
`Basal-H human insulin as compared with the other NPH insulins (P < 0.05; ANOVA and Student's
`t test [67]).
`
`)
`
`biosynthetic human NPH insulin prepa-
`rations are used.
`Time-action profile. Human NPH insu-
`lins were absorbed at a faster rate than
`human zinc insulins Qente insulin) in an
`euglycemic clamp study over 8 h with
`healthy volunteer subjects. The result
`was an increased metabolic effect within
`the first 4 h after injection (66). Thus,
`early after injection, the metabolic effects
`of human NPH and human zinc insulin
`preparations are different from each
`other.
`
`The time-action profiles of four
`widely used human NPH insulin prepa-
`rations were investigated in healthy sub-
`jects using the euglycemic clamp tech-
`nique (Fig. 2) (67). The overall time-
`action profiles were interchangeable. The
`onset of action (defined as half-maximal
`action) of all NPH insulins tested was
`within 2.5—3 h, with peak action after
`
`5-7 h, and duration of action (defined as
`>25% of maximal action) between
`13-16 h. This study showed that there
`are no clinically important differences in
`the duration of action of human NPH
`insulins from different insulin manufac-
`turers.
`Clinical implications. The more rapid
`absorption and sh