The variability in the action of unmodified insulin is more dependent on changes in tissue insulin sensitivity than on insulin absorption

Effects of Unsuppressed Endogenous Insulin on Pharmacokinetics and/or Pharmacodynamics of Study Insulin in the Healthy: A Retrospective Study

C‐peptide, a marker of endogenous insulin, should be consistently inhibited during euglycemic clamping, while an elevated postdosing C‐peptide (CP_postdosing) is not an occasional phenomenon. This was a retrospective study that included 33 men who underwent a manual euglycemic clamp with a subcutaneous injection of insulin aspart (IAsp) aiming to describe the effects of insufficient suppression of endogenous insulin on estimates of the pharmacokinetics and pharmacodynamics of injected insulin. The time profiles of whole blood glucose, human insulin, glucose infusion rate (GIR), and C‐peptide were recorded. The subjects were divided into 2 groups at a ratio of 2:1: group A ([CP_postdosing]_max>baseline CP [CP_baseline]), group B ([CP_postdosing]_max ≤ CP_baseline). The endogenous insulin was approximately equal to the measured value of human insulin or calculated from the C‐peptide. The basal glucose, CP_baseline, basal human insulin, homeostatic model assessment of insulin resistance, IAsp dose, and demographic statistics were all comparable between the 2 groups except the “clamped” glucose. The average clamped glucose was 99.7% (group A) and 94.9% (group B) of baseline. After correction for clamped glucose, GIR area under the concentration‐time curve from time 0 to 8 hours was higher in group A (P < .05) under comparable IAsp exposure. Endogenous insulin area under the concentration‐time curve from time 0 to 8 hours calculated from C‐peptide was different from that measured from human insulin in group A (P < .05), whereas no statistical difference between these measures was observed in group B. Hence, blood glucose should be controlled below the baseline to ensure the inhibition of endogenous insulin. Unsuppressed endogenous insulin may contribute to observed GIR, and the endogenous insulin–corrected pharmacokinetics estimated by C‐peptide may be inaccurate with insufficient endogenous insulin suppression.

Pharmacokinetic and pharmacodynamic equivalence of Biocon's biosimilar Insulin-R with the US-licensed Humulin® R formulation in healthy subjects: Results from the RHINE-1 (Recombinant Human INsulin Equivalence-1) study

AIM

To establish equivalence in the pharmacokinetic (PK) and pharmacodynamic (PD) endpoints between proposed biosimilar Insulin-R (Biocon's Insulin-R) and Humulin® R using the euglycaemic clamp technique in healthy subjects.

MATERIALS AND METHODS

In this phase-1 automated euglycaemic glucose clamp study, 42 healthy subjects were randomized (1:1) to receive a single dose of 0.3 IU/kg of Biocon's Insulin-R and Humulin-R. Plasma insulin concentrations and glucose infusion rates (GIRs) were assessed over 12 hours. Primary PK endpoints were area under the insulin concentration-time curve from 0 to 12 hours (AUC_ins.0-12h ) and maximum insulin concentration (C_ins.max ). Primary PD endpoints were area under the GIR time curve from 0 to 12 hours (AUC_GIR.0-12h ) and maximum GIR (GIR_max ).

RESULTS

Equivalence was demonstrated between Biocon's Insulin-R and Humulin-R for the primary PK and PD endpoints. The 90% confidence intervals were within 80.00% to 125.00% limits. The PK and PD profiles were comparable. There were no significant differences in the safety profiles of the two treatments, and no serious adverse events were reported.

CONCLUSION

PK and PD equivalence was demonstrated between Biocon's Insulin-R and Humulin-R in healthy subjects. Treatment with Biocon's Insulin-R and Humulin-R was well tolerated.

A Conversation on an Effective, Straightforward, Quantitative Approach to the Outpatient Use of Insulin

For primary care providers, using insulin can present challenges that can be met by a straightforward approach using the following principles. Depending on when it is injected, each component of the insulin regimen has a maximal effect on a specific period of the 24-hour cycle (e.g., overnight, morning, afternoon, or evening). The glucose pattern in that period determines whether the dose of that component of the insulin regimen requires adjusting. Regarding which insulin types and insulin regimens to use, human insulin (NPH and regular) is as effective as analog insulins, and a two-injection intensified insulin regimen is as effective as a four-injection regimen.

Pharmacokinetic and Pharmacodynamic Properties of Faster-Acting Insulin Aspart versus Insulin Aspart Across a Clinically Relevant Dose Range in Subjects with Type 1 Diabetes Mellitus

Background

Absorption of current rapid-acting insulins is too slow for patients with diabetes mellitus to achieve optimal postprandial glucose control. Faster-acting insulin aspart (faster aspart) is insulin aspart in a new formulation with faster early absorption. We compared the pharmacokinetic/pharmacodynamic properties of faster aspart and insulin aspart across a clinically relevant dose range.

Methods

In this randomised, double-blind, crossover trial, 46 subjects with type 1 diabetes mellitus received single subcutaneous doses of faster aspart and insulin aspart at 0.1, 0.2 (repeated three times to estimate within-subject variability) and 0.4 U/kg in a euglycaemic clamp setting (target 5.5 mmol/L).

Results

Consistently for the three doses, faster aspart demonstrated faster onset and greater early absorption and glucose-lowering effect versus insulin aspart. Across all three doses, onset of appearance occurred approximately twice as fast (approximately 5 min earlier) and early insulin exposure (AUC_{IAsp,0–30min}) was approximately 1.5- to 2-fold greater for faster aspart versus insulin aspart. Likewise, onset of action occurred approximately 5 min faster and early glucose-lowering effect (AUC_{GIR,0–30min}) was approximately 1.5- to 2-fold larger for faster aspart versus insulin aspart. Relative bioavailability was approximately 100% and total glucose-lowering effect was similar for faster aspart versus insulin aspart. Dose–concentration and dose–response relationships were comparable between faster aspart and insulin aspart. Within-subject variability in glucose-lowering effect was low for faster aspart (coefficient of variation approximately 20%) and not significantly different from insulin aspart.

Conclusion

The faster onset and greater early insulin exposure and glucose-lowering effect with faster aspart versus insulin aspart are preserved across a broad range of doses and consistently observed from day to day.

ClinicalTrials.gov identifier

NCT02033239.

Electronic supplementary material

The online version of this article (doi:10.1007/s40262-016-0473-5) contains supplementary material, which is available to authorized users.

Factors Affecting the Absorption of Subcutaneously Administered Insulin: Effect on Variability

Variability in the effect of subcutaneously administered insulin represents a major challenge in insulin therapy where precise dosing is required in order to achieve targeted glucose levels. Since this variability is largely influenced by the absorption of insulin, a deeper understanding of the factors affecting the absorption of insulin from the subcutaneous tissue is necessary in order to improve glycaemic control and the long-term prognosis in people with diabetes. These factors can be related to either the insulin preparation, the injection site/patient, or the injection technique. This review highlights the factors affecting insulin absorption with special attention on the physiological factors at the injection site. In addition, it also provides a detailed description of the insulin absorption process and the various modifications to this process that have been utilized by the different insulin preparations available.

Unblinded CGM Should Replace Blinded CGM in the Clinical Management of Diabetes

The original continuous glucose monitors (CGMs) were limited to 3-day, blinded observation periods where glucose data was hidden from patients and later retrospectively analyzed by a provider to help guide the management of diabetes. Unblinded CGM, released several years later, allows patients to view their glucose data in real-time amidst their daily routines, enabling them to better understand how variables such as activity, nutrition, and medications affect glucose levels. Research studies consistently demonstrate improved glycemic control and reduced hypoglycemia in children and adults with type 1 and type 2 diabetes while using unblinded CGM.(1-4) As such, we believe that all CGM usage in clinical practice should be in real-time, unblinded mode for short-term and long-term wear periods.

Insulin analogs--is there a compelling case to use them? No!

The availability of insulin analogs has offered insulin replacement strategies that are proposed to more closely mimic normal human physiology. Specifically, there are a considerable number of reports demonstrating that prandial insulin analogs (lispro, aspart, glulisine) have pharmacokinetic and pharmacodynamic profiles closer to normal, with resulting faster onset and offset of insulin effect when compared with regular human insulin. In addition, basal insulin analogs (glargine, detemir) have been reported to offer longer duration of action, less variability, more predictability, less hypoglycemia (especially nocturnal), and a favorable effect on weight. However, an argument against use of analog insulins as compared with use of regular or NPH insulin is one that states that the effectiveness and risk of hypoglycemia are the only two valid clinical outcomes that should be used to compare the analog and human insulins. Thus, there remains a debate in some circles that analog insulins are no more effective than human insulins, yet at a much higher financial cost. To provide an in-depth understanding of both sides of the argument, we provide a discussion of this topic as part of this two-part point-counterpoint narrative. In the counterpoint narrative presented here, Dr. Davidson provides his argument and defends his opinion that outside of a few exceptions, analog insulins provide no clinical benefit compared with human insulins but cost much more. In the preceding point narrative, Dr. Grunberger provides a defense of analog insulins and their value in clinical management and suggests that when evaluating the “cost” of therapy, a much more global assessment is needed.

Variability of glucose-lowering effect as a limiting factor in optimizing basal insulin therapy: a review

Lowering blood glucose with insulin therapy towards beneficial target levels while also avoiding hypoglycaemia is a challenging task. An important confounding factor, which might be under-appreciated in this scenario, is that of variable glucose readings causing difficulties with dose adjustment. Furthermore, this glucose variability is, to some extent, a reflection of variability in the glucose-lowering action of the insulin therapy itself. Not only is glucose variability a major confounding factor in disease management but it is possibly also of direct prognostic consequence and is increasingly recognized as an informative measurement in diabetes management. The scope for insulin-induced glucose variability is particularly great with basal insulins because of their prolonged absorption from high-dose depots. Pharmacodynamic (PD) variability manifests as both fluctuations in the level of glucose-lowering effect over time, and as inconsistencies in the response from one injection to another. Well-controlled pharmacokinetic (PK)/PD studies using repeated isoglycaemic clamp methodology clearly how that many injected basal insulin products have high variable absorption with correspondingly variable action. Incomplete resuspension and precipitation appear to be important issues with regard to unpredictability in this action, while an inadequate duration of action relative to the dosing interval results in a fluctuating action profile. There are some ultra-long-acting basal insulins with novel protraction mechanisms currently in clinical development for which clamp studies show markedly improved PK/PD profiles.

Dynamic insulin on board: incorporation of circadian insulin sensitivity variation

BACKGROUND

Insulin-on-board (IOB) estimation is used in modern insulin therapy with continuous subcutaneous insulin infusion (CSII) as well as different automatic glucose-regulating strategies (i.e., artificial pancreas products) to prevent insulin stacking that may lead to hypoglycemia. However, most of the IOB calculations are static IOB (sIOB): they are based only on approximated insulin decay and do not take into account diurnal changes in insulin sensitivity.

METHODS

A dynamic IOB (dIOB) that takes into account diurnal insulin sensitivity variation is suggested in this work and used to adjust the sIOB estimations. The dIOB function is used to correct the dosage of insulin boluses in light of this circadian variation.

RESULTS

Basal-bolus as applied by pump users and model predictive control therapy with and without dIOB were evaluated using the University of Virginia/Padova metabolic simulator. Three protocols with four meals of 1 g carbohydrate/kg body weight were evaluated: a nominal scenario and two robustness scenarios, one in which insulin sensitivity was 15% greater than estimated and the other where the lunch is 30% less than announced. In the nominal and robustness scenarios, respectively, the dIOB led to 6% and 24% and 40% less hypoglycemia episodes than approaches without IOB. The new approach was also compared with the sIOB to evaluate the improvements with respect to the previous approach.

CONCLUSIONS

Improved glucose regulation was demonstrated using the dIOB where circadian insulin sensitivity is used to adjust IOB estimation. Use of diurnal variations of insulin sensitivity appears to promote effective and safe insulin therapy using CSII or artificial pancreas. Clinical trials are warranted to determine whether nocturnal hypoglycemia can be reduced using the dIOB approach.

Insulin depot formation in subcutaneoue tissue

BACKGROUND

The size and geometry of an insulin depot that is formed during subcutaneous administration by an insulin pump is evaluated. A novel method is used to visualize accurately the depot formation for small volumes of insulin (of the order of 10-100 µl) at a given point in time. Conventional visualization methods such as magnetic resonance imaging are unable to provide such accurate measurements because of their coarse imaging resolution and long measurement time.

METHODS

The described method consists of subcutaneously infusing dyed insulin into porcine tissue and subsequently shock freezing it with liquid nitrogen. The frozen sample is then sliced into thin layers using a cryomicrotome. A digital image of each layer is taken and then processed with proprietary software, which identifies the dyed areas on each layer and reconstructs a three-dimensional model of the insulin depot with a planar resolution of 30 × 30 µm(2) and a depth resolution of 100 µm. Since this process is not viable for living organisms, porcine tissue was used immediately following slaughter of the animal.

RESULTS

To date, it is most often assumed that the insulin depot takes the shape of a sphere around the tip of the cannula (e.g., 50 µl insulin equates to a spherical radius of 2.3 mm). However, in practice, such a depot form is never observed. Instead, the insulin depot initially spreads laterally (i.e., parallel) to the skin surface and in the collagen matrix that binds the adipose cells together. The depot outreach increases with larger infused volumes, e.g., maximum outreach measured at 5.0/5.7/7.1 mm (quartiles, n = 17) for 50 µl of infused insulin. Beyond a given infused volume (approximately 100 µl), the insulin also starts to spread perpendicular to the skin surface.

CONCLUSIONS

It is concluded that formation of the insulin depot depends on the opening of channels at the boundaries between adipose cells. Hence the insulin follows a path of least resistance and depot formation is determined by the local structure of the subcutaneous tissue.

Visualization of subcutaneous insulin injections by x-ray computed tomography

We report how the three-dimensional structure of subcutaneous injections of soluble insulin can be visualized by x-ray computed tomography using an iodine based contrast agent. The injections investigated are performed ex vivo in porcine adipose tissue. Full tomography scans carried out at a laboratory x-ray source with a total acquisition time of about 1 min yield CT-images with an effective pixel size of 109 × 109 μm². The depots are segmented using a modified Chan-Vese algorithm and we are able to observe differences in the shape of the injection depot and the position of the depot in the skin among equally performed injections. To overcome the beam hardening artefacts, which affect the quantitative prediction of the volume injected, we additionally present results concerning the visualization of two injections using synchrotron radiation. The spatial concentration distribution of iodine is calculated to show the dilution of the insulin drug inside the depot. Characterisation of the shape of the depot and the spatial concentration profile of the injected fluid is important knowledge when improving the clinical formulation of an insulin drug, the performance of injection devices and when predicting the effect of the drug through biomedical simulations.

Immunological responses to exogenous insulin

Regardless of purity and origin, therapeutic insulins continue to be immunogenic in humans. However, severe immunological complications occur rarely, and less severe events affect a small minority of patients. Insulin autoantibodies (IAAs) may be detectable in insulin-naive individuals who have a high likelihood of developing type 1 diabetes or in patients who have had viral disorders, have been treated with various drugs, or have autoimmune disorders or paraneoplastic syndromes. This suggests that under certain circumstances, immune tolerance to insulin can be overcome. Factors that can lead to more or less susceptibility to humoral responses to exogenous insulin include the recipient's immune response genes, age, the presence of sufficient circulating autologous insulin, and the site of insulin delivery. Little proof exists, however, that the development of insulin antibodies (IAs) to exogenous insulin therapy affects integrated glucose control, insulin dose requirements, and incidence of hypoglycemia, or contributes to beta-cell failure or to long-term complications of diabetes. Studies in which pregnant women with diabetes were monitored for glycemic control argue against a connection between IAs and fetal risk. Although studies have shown increased levels of immune complexes in patients with diabetic microangiopathic complications, these immune complexes often do not contain insulin or IAs, and insulin administration does not contribute to their formation. The majority of studies have shown no relationship between IAs and diabetic angiopathic complications, including nephropathy, retinopathy, and neuropathy. With the advent of novel insulin formulations and delivery systems, such as insulin pumps and inhaled insulin, examination of these issues is increasingly relevant.

Subcutaneous insulin: pharmacokinetic variability and glycemic variability

The therapeutic goal in insulin-treated diabetic patients is to maintain on the long-term a tight glucose control (HbA1, < 6.5-7% or less) through an insulin regimen which "mimic" the physiological insulin profile: a basal insulin secretion to maintain glucose homeostasis and an acute post-prandial secretion in response to meal intake. Such goal represents a challenge for the clinician as conventional human insulins have major drawbacks: slow absorption and too late peak with regular insulins, delayed peak and often occuring at an unwanted time with intermediate and long-acting insulins. Furthermore, these insulins are characterised by a large within- and between-subjects variability, which complicate patients' task to self-adapt their daily doses, even for those well educated and compliants. These limitations and unpredictable variations in insulin action are responsible for an increased risk of hypoglycemic events, between meals as well as during the night period. As a consequence, glucose control is frequently insufficient in type 1 diabetic patients, and these limitations may contribute also to the delayed initiation of insulin therapy in type 2 diabetics when oral antidiabetic agents fail. This variability and the non-reproducibility of the conventional insulin pharmacodynamics are explained by several exogenous and endogenous factors describe in this review. Availability of new short-acting (lispro, aspart and glulisine) and long-acting analogs (glargine, detemir) of human insulin, with improved pharmacokinetic characteristics, and a lesser variability and better reproducibility, should facilitate a tight glucose control in insulin-treated patients. The main pharmacokinetic and pharmacodynamic characteristics of these new insulin analogs are presented and discussed in the light of there intra- and inter-individual variability. Their reduced variability should permit to reinforce near "physiological" insulin regimen such as "basal-bolus" technique and to consider new approaches and therapeutic strategies in type 1 and type 2 diabetic patients.

Is insulin detemir able to favor a lower variability in the action of injected insulin in diabetic subjects?

Insulin treated diabetic patients have often to contend with variability in the action of injected insulin and to some unpredictibility in glycemic control. The variability in blood glucose control seems particularly important with long-acting insulins. Insulin detemir belongs to a new class of non-crystalline form of long-acting insulin analogs. Absorption of insulin detemir is dependent on neither appropriate resuspension before injection and dissolution of crystals in the subcutaneous tissue, as is the case for NPH insulin, nor on formation and dissolution of microprecipitates, as is the case for insulin glargine. In euglycemic glucose clamp studies, insulin detemir was associated with significantly less within-subjects variability for the pharmacodynamic endpoints than both NPH insulin and insulin glargine. Three, up to 6 months trials, carried out in patients with type 1 diabetes have shown that the day-to-day within-subject variations in plasma glucose were significantly lower with insulin detemir than with human NPH insulin. Similar results have been reported in patients with type 2 diabetes. Nightly 8-h plasma glucose recordings showed a smoother and more stable profile with insulin detemir than with NPH insulin. In patients with type 1 diabetes the combination of insulin detemir with mealtime insulin aspart, a fast-acting insulin analog, provides a smoother and more stable profile with lower post-prandial plasma glucose levels that the combination of NPH insulin with regular human insulin before each meal. In several trials, the risk of hypoglycemia, particularly of nocturnal hypoglycemia, was significantly lower with insulin detemir than with NPH insulin. In conclusion insulin detemir offers a better reproducibility as compared with other basal insulins, reduces the risk of hypoglycemia, and may lead the patients to titrate their insulin doses more easily and therefore to achieve more often glycemic objectives. The combination of rapid- and long-acting insulin analogs reproduces a more physiological insulin secretion and thereby reduces the risk of hypoglycemia and improves the overall 24-h glycemic profile.

Properties of pramlintide and insulin upon mixing

PURPOSE

The pharmacokinetics, pharmacodynamics, and safety of pramlintide and various insulin formulations in patients with type 1 diabetes mellitus (DM) when given as separate injections or mixed in the same syringe before injection were studied.

METHODS

In two randomized, open-label, placebo-controlled, five-period-crossover studies, patients with type 1 DM received preprandial injections of pramlintide, short-acting insulin, and long-acting insulin administered either by separate injections or after mixing in various combinations. Serum free insulin and plasma glucose concentrations were measured for 10 hours and plasma pramlintide concentrations for 5 hours after injection.

RESULTS

Blood samples were collected from a total of 51 patients. All treatments involving mixtures were comparable to separate injections with respect to the area under the concentration-versus-time curve (AUC) and the maximum concentration (Cmax) of serum free insulin. There were some minor differences in the AUC and Cmax of pramlintide. No injection-site reactions or other unexpected adverse events were observed.

CONCLUSION

Mixing pramlintide with short- or long-acting insulin in the same syringe before subcutaneous injection did not affect the pharmacodynamics of glucose or the pharmacokinetics of insulin or pramlintide in a clinically significant manner.

Intrasubject variability of inhaled insulin in type 1 diabetes: a comparison with subcutaneous insulin

We compared intrasubject variability of insulin and glucose profiles after a standardized meal between insulin inhaled via the AERx insulin Diabetes Management System (AERx iDMS, Aradigm Corp., Hayward, CA) and given as a subcutaneous injection. In this single-center, parallel, randomized, open-labeled trial, 17 male, non-smoking patients with type 1 diabetes (mean age, 27.7 years; body mass index, 23.4 kg/m(2)) received a fixed, individualized dose of human insulin, on four treatment days followed by an individualized breakfast, administered either by inhalation via AERx iDMS (n = 9) or by subcutaneous injection. Serum insulin and serum glucose levels were determined at regular intervals for 6 h postdose. Intrasubject variability was expressed as coefficient of variation. No statistically significant differences in intrasubject variability were observed between the treatments for the areas under the insulin curves for 0-6 h [27% vs. 19% (inhaled insulin vs. subcutaneous)] and areas under the glucose curves 0-6 h (30% vs. 23%). Intrasubject variability values for insulin half-life, terminal elimination rate constant, and mean residence time were significantly less in the inhaled insulin group compared with the subcutaneous insulin group (P = 0.01-0.02). Only one potentially trial product-related adverse event (an audible wheeze) was reported, and no clinically relevant changes in pulmonary function were detected. The intrasubject variability was comparable between patients receiving inhaled insulin and subcutaneous insulin, thereby confirming the reproducibility of administering insulin via AERx iDMS. Inhaled insulin was well tolerated and is a feasible alternative to subcutaneous insulin in patients with type 1 diabetes.

Lower within-subject variability of insulin detemir in comparison to NPH insulin and insulin glargine in people with type 1 diabetes

The aim of this randomized double-blind study was to compare the within-subject variability of the glucose-lowering effect of a novel insulin analog, insulin detemir, with that of insulin glargine and NPH insulin in people with type 1 diabetes. Fifty-four subjects (32 males and 22 females, age 38 +/- 10 years [mean +/- SD], BMI 24 +/- 2 kg/m(2), HbA(1c) 7.5 +/- 1.2%, diabetes duration 18 +/- 9 years) participated in this parallel group comparison. Each subject received four single subcutaneous doses of 0.4 units/kg of either insulin detemir (n = 18), insulin glargine (n = 16), or human NPH insulin (n = 17) under euglycemic glucose clamp conditions (target blood glucose concentration 5.5 mmol/l) on four identical study days. The pharmacodynamic (glucose infusion rates [GIRs]) and pharmacokinetic (serum concentrations of insulin detemir, human insulin, and insulin glargine) properties of the basal insulin preparations were recorded for 24 h postdosing. Insulin detemir was associated with significantly less within-subject variability than both NPH insulin and insulin glargine, as assessed by the coefficient of variation (CV) for the pharmacodynamic end points studied [GIR-AUC((0-12 h)) 27% (detemir) vs. 59% (NPH) vs. 46% (glargine); GIR-AUC((0-24 h)) 27 vs. 68 vs. 48%; GIR(max) 23 vs. 46 vs. 36%; P < 0.001 for all comparisons]. Insulin detemir also provided less within-subject variability in the pharmacokinetic end points: maximal concentration (C(max)) 18 vs. 24 vs. 34%; INS-AUC((0- infinity )) 14 vs. 28 vs. 33%. The results suggest that insulin detemir has a significantly more predictable glucose-lowering effect than both NPH insulin and insulin glargine.

Absorption and metabolic effect of inhaled insulin: intrapatient variability after inhalation via the Aerodose insulin inhaler in patients with type 2 diabetes

OBJECTIVE

To compare the intrapatient variability of the pharmacokinetic and pharmacodynamic responses to inhaled regular insulin (INH) delivered via the Aerodose Insulin Inhaler with that of subcutaneously injected regular insulin (SC) in patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 15 patients with type 2 diabetes (nonsmokers, 10 men, aged 47-77 years) received two 240-unit doses of INH, delivered via a clinical Aerodose Insulin Inhaler and two 24-unit doses of SC under euglycemic clamp conditions on four separate study days. Glucose infusion rates (GIRs) and serum insulin concentrations were monitored over the following 8 h. Comparisons of intrapatient coefficients of variation (CV) were used to assess the reproducibility of INH versus SC.

RESULTS

INH showed a bioavailability (0-8 h postdosing) of 16% and biopotency of 13% relative to SC. Comparison of the CVs (%) for area under the curve for serum insulin and GIR between INH and SC showed no significant differences between the treatments during 0-3 h (19% for INH versus 23% for SC) or 0-8 h (22% for INH versus 16% for SC). INH exhibited a shorter time to peak insulin concentration (T(max) [mean +/- SD] 76 +/- 51 vs. 193 +/- 66 min) and shorter time to peak metabolic effect (T(GIRmax) 170 +/- 53 vs. 244 +/- 75 min) compared with SC (P < 0.001). No adverse events were observed.

CONCLUSIONS

Comparable dosing reproducibility and shorter time to peak action of INH compared with SC suggest that INH delivered via the Aerodose Insulin Inhaler can provide reliable preprandial dosing of insulin in patients with type 2 diabetes.

Insulin aspart: promising early results borne out in clinical practice

The novel, rapid-acting insulin analogue insulin aspart (IAsp; Novo Nordisk) has been shown in preclinical studies to be more rapidly absorbed than human insulin (HI) when administered subcutaneously. IAsp reaches higher peak serum concentrations in a shorter time than HI, whilst maintaining a similar receptor binding and safety profile. The physiological pharmacokinetic profile of IAsp compared to that of HI has been demonstrated in both adult and paediatric populations and was accompanied by small but statistically significant reductions in HbA(1c), lower postprandial glucose excursions and a reduced risk of late postprandial and major nocturnal hypoglycaemia. Benefits may be maximised by dose optimisation, using bolus doses that result in effective postprandial glucose reduction, as well as higher and multiple basal insulin doses. The safety profile, including cardiovascular risk, is equivalent to HI.

Variability of insulin absorption and insulin action

Subcutaneous (s.c.) injections of identical insulin doses may lead to considerable intra- and inter-individual differences in the current metabolic control of patients with diabetes mellitus. This well-known variability of the metabolic effect of insulin hampers practical insulin therapy considerably. The aim of this review is to summarize the knowledge about this topic, with a special focus on the variability of insulin action after pulmonary administration of insulin. A number of studies have been published describing the variability of insulin absorption from the s.c. depot. Only in a few published studies has the variability of insulin action after s.c. administration been quantified. Under controlled experimental conditions s.c. injections of regular insulins result in an intra-individual coefficient of variation (CV) of 15-25% of certain pharmacodynamic summary measures--which characterize the metabolic effect of the applied insulin--in healthy subjects. The inter-individual variability was approximately 10% higher than the intra-individual variability. Subcutaneously injected intermediate- and long-acting insulin preparations were described to have an even greater variability (> 50%) than subcutaneously injected regular insulin. However, in a glucose clamp study s.c. application of NPH insulin led to an intra-individual CV in the range of 12-45% in healthy subjects. The reason for this discrepancy might be that the NPH insulin suspension was sufficiently shaken prior to drawing up the dose. Compared with conventional insulin formulations, rapid- and long-acting insulin analogues appear to have a similar variability, which means that, unfortunately, no considerable advantages in terms of variability were achieved by the invention of these novel insulin preparations. There are no appropriate studies available investigating the variability of the metabolic effect after s.c. insulin administration in patients with diabetes. The inhalation of insulin is a novel form of insulin administration that is currently under clinical development. The variability of the metabolic effect induced by the inhalation of insulin has up to now only been investigated in a small number of (published) studies. In a glucose-clamp study with healthy subjects the inhalation of an identical insulin dose on three study days led to an intra-individual variability that was comparable to that after s.c. injection of regular insulin. In a dose-response study with patients with type 1 diabetes the intra-individual CV was 34% for the area under the curve of the glucose infusion rate for 0-10 h. Studies with patients with type 2 diabetes have shown that the intra-individual CVs were within the range seen after s.c. insulin administration or even lower. In summary, the intra-individual variability of the metabolic effect observed after insulin application, be it subcutaneously injected or be it inhaled, is considerable and, therefore, hampers practical diabetes therapy. To date no means have been found that could lead to a clinically relevant reduction in the variable metabolic effect.

Recombinant DNA technology in the treatment of diabetes: insulin analogs

After more than half a century of treating diabetics with animal insulins, recombinant DNA technologies and advanced protein chemistry made human insulin preparations available in the early 1980s. As the next step, over the last decade, insulin analogs were constructed by changing the structure of the native protein with the goal of improving the therapeutic properties of it, because the pharmacokinetic characteristics of rapid-, intermediate-, and long-acting preparations of human insulin make it almost impossible to achieve sustained normoglycemia. The first clinically available insulin analog, lispro, confirmed the hopes by showing that improved glycemic control can be achieved without an increase in hypoglycemic events. Two new insulin analogs, insulin glargine and insulin aspart, have recently been approved for clinical use in the United States, and several other analogs are being intensively tested. Thus, it appears that a rapid acceleration of basic and clinical research in this arena will be seen, which will have direct significance to both patients and their physicians. The introduction of new short-acting analogs and the development of the first truly long-acting analogs and the development of analogs with increased stability, less variability, and perhaps selective action, will help to develop more individualized treatment strategies targeted to specific patient characteristics and to achieve further improvements in glycemic control. Data on the currently available and tested analogs, as well as data on those currently being developed, are reviewed.

Current understanding of feline diabetes: part 2, treatment

When treating diabetic cats, the primary aim is to control clinical signs without causing clinical hypoglycaemia. Secondary goals are to maximise the chances of attaining diabetic remission and to minimise the risk of complications due to chronic hyperglycaemia. A treatment plan that is convenient for the owner is important for compliance. Underweight or overweight diabetic cats should be fed with the aim of normalising bodyweight. Current evidence suggests that non-obese diabetic cats can be fed ad libitum. The oral hypoglycaemic drug glipizide is well established as a treatment for about a third of diabetic cats, which have residual beta cell function. Preliminary studies on other oral agents such as vanadium salts, metformin, and troglitazone indicate a potential use in some diabetic cats. Insulin treatment remains the treatment of choice for the majority of diabetic cats. Choice of insulin, dose rates and monitoring of treatment are discussed.