Diabetes Care 30:2571-2576, 2007 DOI: 10.2337/dc06-2589 © 2007 by the American Diabetes Association
The Effect of Exercise on the Absorption of Inhaled Human Insulin via the AERx Insulin Diabetes Management System in People With Type 1 Diabetes
1 Department of Internal Medicine, Medical University Graz, Graz, Austria Address correspondence and reprint requests to Astrid Heide Petersen, Novo Nordisk A/S, Novo Allé, DK-2880 Bagsvaerd, Denmark. E-mail: ashp{at}novonordisk.com
OBJECTIVE—This study investigated the effect of moderate exercise on the absorption of inhaled insulin via the AERx insulin diabetes management system (iDMS). RESEARCH DESIGN AND METHODS—In this randomized, open-label, four-period, crossover, glucose clamp study 23 nonsmoking subjects with type 1 diabetes received a dose of 0.19 units/kg inhaled human insulin followed in random order by either 1) no exercise (NOEX group) or 30 min exercise starting, 2) 30 min after dosing (EX30), 3) 120 min after dosing (EX120), or 4) 240 min after dosing (EX240). RESULTS—Exercise changed the shape of the free plasma insulin curves, but compared with the NOEX group the area under the curve for free plasma insulin (AUCins) for the first 2 h after the start of exercise was unchanged for EX30 and EX240, while it was 15% decreased for EX120 (P < 0.01). The overall insulin absorption during 6 and 10 h after dosing was 13% decreased for EX30 (P < 0.005), 11% decreased for EX120 (P < 0.01), and unchanged for EX240. Exercise did not influence the maximum insulin concentration (Cmax), while the time to Cmax was 22 min earlier for EX30 (P = 0.04). The AUC for the glucose infusion rate (AUCGIR) for 2 h after the start of exercise increased by 58% for EX30, 45% for EX120, and 71% for EX240 (all P < 0.02) compared with the NOEX group. CONCLUSIONS—Thirty minutes of moderate exercise led to unchanged or decreased absorption of inhaled insulin via AERx iDMS and faster Cmax for early exercise. Thus, patients using AERx iDMS can adjust insulin dose as usual independent of time of exercise, but they should be aware of the faster effect if exercising early after dosing.
Abbreviations: AUC, area under the curve GIR, glucose infusion rate iDMS, insulin diabetes management system IPAC, International Physical Activity Questionnaire
Ever since the introduction of insulin injections 80 years ago, alternatives to injections of insulin have been sought after (1,2). Today, inhaled human insulin is an alternative to injected meal-time insulin, with the first product on the market and several systems in development (3). The AERx insulin diabetes management system (iDMS) (insulin inhaler and disposable insulin strips) is one such system and is currently under development by Novo Nordisk (Bagsvaerd, Denmark). The system allows dose adjustment in single-unit increments and ensures delivery of inhaled insulin to the deep lung by means of electronically controlled release of a fine-particle insulin aerosol only when the inspiratory flow rate and inhaled volume of the user are optimal for deep-lung delivery (breath check) (4). Numerous studies have been performed with inhaled insulin over the last 10 years, investigating, among others, the effect of smoking (5,6), upper respiratory tract infection (7), age (8), and asthma (9). Despite the many studies on inhaled insulin, limited information is available on the effect of physical activity on the absorption of inhaled insulin. Regular physical activity is an important part of the treatment of diabetes and is recommended to all groups of people with diabetes (10). Large tidal volume ventilation after dosing leads to increased absorption of inhaled insulin in rabbits (11), and increased serum levels of inhaled insulin have been reported in humans after performance of pulmonary function test maneuvers, which included deep breathing (12). Increased absorption/absorption rate as an effect of exercise is well known for other inhaled substances such as technetium 99m-labeled diethylene triamine penta-acetic acid (13,14), nedocromil sodium (15), and terbutaline (16). In a recent preliminary study in healthy volunteers who exercised after inhalation of insulin via a nebulizer system, we saw clinically relevant effects of exercise (17) and thus warranted further investigations in people with type 1 diabetes who respond differently to exercise than healthy people (18). People with diabetes might perform increased physical activity (exercise) at different time points after dosing, and the impact of timing of exercise on insulin absorption is therefore of interest. Thus, the purpose of this study was to investigate the effect of exercise on the absorption of inhaled insulin via the AERx iDMS when performed at three clinically relevant time points.
This study was carried out according to the principles of the Declaration of Helsinki (19) and good clinical practice (20). All subjects gave written informed consent before any study-related activities.
Twenty-three male and female subjects with type 1 diabetes were included in the study. The following were the inclusion criteria: aged between 18 and 65 years (both inclusive), BMI On separate days, in randomized order, all subjects received four treatments: inhaled human insulin and 1) no exercise (NOEX group) or exercise starting, 2) 30 min after dosing (EX30), 3) exercise starting 120 min after dosing (EX120), and 4) exercise starting 240 min after dosing (EX240). The time point of 30 min after dosing was chosen as the earliest clinically relevant time of exercise after insulin inhalation, the time point of 240 min after dosing was chosen as a late time point for exercise, while the time point of 120 min after dosing was chosen as an intermediate time point. The subjects attended each dosing day in the morning in a fasting state and remained fasting and in supine position, except for periods of exercise, during the study day. Subjects on multiple injections of insulin injected their last insulin dose before 8:00 P.M. the day before. Subjects on long-acting insulin analogs were transferred to NPH insulin at least 3 days before each dosing day. Subjects on continuous subcutaneous insulin treatment stopped their insulin infusion upon admission.
A hand or antecubital vein was cannulated and kept in a thermoregulated box ( Blood samples for total serum insulin were drawn in intervals of 5–60 min during the dosing days. To assure accurate estimation of free insulin concentrations, immediate centrifugation of the blood samples and extraction of insulin antibodies by polyethylene glycol precipitation were performed (21). Free plasma human insulin was measured using a commercially available enzyme-linked immunosorbent assay (Dako, Cambridgeshire, U.K.) at Capio Diagnostik (Copenhagen, Denmark).
Dosing
Exercise protocol
Safety
Statistical methods
In all cases, AUC was calculated by means of the trapezoidal rule. AUCins(30–150 min) was transformed with the natural logarithm and analyzed by an ANOVA model including treatment as fixed effect and subject as random effect. The secondary end points [AUCins(120–240 min), AUCins(240–360 min), AUCins(0–360 min), AUCins(0–600 min), Cmax, tmax, The pharmacodynamic end points [AUC for the glucose infusion rate (GIR): AUCGIR(30–150 min), AUCGIR(120–240 min), AUCGIR(240–360 min), AUCGIR(0–360 min), and AUCGIR(0–600 min)] were calculated and analyzed similar to the corresponding pharmacokinetic end points. Individual GIR profiles were smoothed by a LOESS function, and GIRmax and tGIRmax were calculated from smoothed GIR profiles and analyzed similarly to Cmax and tmax. Data from the IPAQ questionnaire were summarized (24) in categories and in metabolic equivalent minutes (MET-min), where MET-min is approximately equivalent to kilocalories for a 60-kg person. A significance level of 5% was used throughout, and all tests were made against the NOEX group.
A total of 29 subjects were screened, and 23 subjects were randomized in the study: 8 women and 15 men, all were Caucasians, all were aged (mean [range]) 34.7 years (21.3–46.4), had BMI 24.5 kg/m2 (19.8–28.4), had diabetes duration 17.6 years (4.2–40.8), had an A1C 7.8% (6.0–10.2), and all were C-peptide negative. Two subjects were withdrawn; one withdrew due to an adverse event (circulatory collapse during exercise) at the first dosing visit, and one withdrew consent after two dosing visits due to private time schedule issues. Thus, 21 subjects completed the study. All 23 subjects exposed were included in the safety evaluation, while 22 subjects with at least one full free plasma insulin or GIR profile were included in the pharmacokinetic and pharmacodynamic analyses. The subjects reflected a normal population, with 44% being in the IPAQ "high" activity category, 39% being in the IPAQ "moderate" activity category, and 17% being in the IPAQ "low" activity category and with a VO2max of (means ± SD) 40 ± 7 ml · min–1 · kg–1 and a total median activity score of 2,457 MET-min/week (range 396–15,039).
Exercise
Pharmacokinetic results
Pharmacodynamic results As clearly seen in Fig. 1, the glucose need increased during periods of exercise, with GIRmax related to exercise periods (Table 1). Thus, the AUCGIR for the 2 h after start of exercise was increased for all exercise treatment (Table 1). The overall need for glucose over 6 and 10 h [AUCGIR(0–360 min) and AUCGIR(0–600 min)] was not significantly changed for EX30 compared with the NOEX group (Table 1), while it increased for EX120. For EX240, AUCGIR(0–360 min) was increased, while the increase for AUCGIR(0–600 min) did not reach statistical significance (P = 0.09).
Safety
This is the first trial investigating the effects of moderate exercise after administration of inhaled insulin in subjects with type 1 diabetes. Exercise is a recommended treatment option in both type 1 and type 2 diabetes for achieving good metabolic control. Therefore, in this study we investigated the effect of exercise at three different time points (30, 120, and 240 min after inhalation). During exercise, an increase in the pharmacokinetic profiles was observed, which was followed by a sharp decline in plasma insulin concentration to below the level of no exercise after stopping exercise. Consequently, compared with no exercise, the absorption over 2 h after the start of exercise was unchanged for exercise 30 and 240 min after dosing, while it was decreased for exercise 120 min after dosing. Cmax was unchanged by exercise but came earlier for exercise 30 min after dosing. The overall absorption was slightly decreased or unchanged.
These obtained data are in contrast to what has been obtained in a study with terbutaline (16), where an The exercise setup was identical, and the physiological effect of exercise (including ventilation) was comparable between the two studies. Thus, an explanation must be found in other parameters. In observational and experimental studies, an association between diabetes and reduced lung function (25–29), as well as reduced lung diffusion response to exercise (30), has been found. This change could potentially be a part of the explanation for the difference between this study and the previous study (17). Moreover, in the present study, the insulin dose was delivered with the AERx iDMS in one or two inhalations with smaller particles, whereas in the previous study the dose was delivered over 23 voluntary deep breaths by a nebulizer system, which provided a larger particle size (17). This might lead to a difference in deposition, which might influence absorption. However, a recent study (31) with technetium 99m-labeled diethylene triamine penta-acetic acid has shown that deposition might not affect absorption as much as previously anticipated, suggesting that other mechanisms might be involved as well. Another unexpected finding is decreased overall insulin absorption after exercise. This could either be explained by less available insulin in the lung for absorption, less absorbed insulin, or increased elimination in the blood. As the insulin is already deposited for awhile in the deep lung at the time of exercise, it is unlikely that insulin is exhaled. Another speculation is whether exercise leads to increased degradation of insulin in the lung by increased macrophage activity or increased mucociliary clearance, as has been seen with centrally deposited albumin (32). However, this has not been observed for albumin delivered to the deep lung (33). No difference was found in the terminal absorption rate (represented by the terminal elimination rate, as the absorption is the rate-limiting factor for disappearance of insulin from plasma [flip-flop situation]) or in the mean residence time; thus, there is no indication of a general effect on the absorption rate or elimination. All in all, this finding of decreased absorption remains unexplained and needs to be investigated in future studies.
In general, the pharmacodynamic results supported the pharmacokinetic findings. In each of the exercise intervals, the infusion rate of glucose increased as expected, reflecting a combined effect of the insulin absorption and exercise, followed by a decrease, in line with the concomitant decrease in insulin. For exercise 240 min after dosing, the glucose need was higher than for no exercise, probably reflecting only the exercise itself, making it possible to quantify the glucose need during 30 min moderate cycle exercise to The inhaled insulin was well tolerated by all subjects. One person experienced a circulatory collapse, which was considered unlikely to be caused by the insulin. However, although the used dose was of usual clinical sizes, insulin is known to cause vasodilatory effects (35,36), which might have contributed. The physical activity level in this study reflects daily life activities, such as biking to work at moderate pace and similar. No conclusions can be drawn about higher levels or longer periods of exercise. This would need to be investigated. Due to the number of acceptable clamps per subject, it was unfortunately not possible to include subcutaneous treatment arms. Thus, as no direct comparison within the study was feasible, it is not possible to directly compare with the effect of exercise on subcutaneous regular human insulin or a rapid-acting analog. However, the relatively small changes in the pharmacokinetics support the use of insulin in connection with exercise with similar precautions as for subcutaneous insulin. Only patients performing exercise early after dosing should be aware of the faster maximal insulin concentration at this time point of exercise. This present study also illustrates the well-known increased metabolic effect of exercise in itself and supports the need for either extra carbohydrate intake or reduction in insulin dose in connection with exercise. The variability observed confirms the need for frequent blood glucose measurements in relation to exercise, at least until the person is aware of his/her own response to the new insulin regimen and exercise. In summary, 30 min moderate exercise at 30, 120, or 240 min after dosing of inhaled human insulin led to 1) unchanged or decreased absorption over the first 2 h, 2) unchanged or decreased overall absorption, and 3) unchanged maximal insulin concentration compared with no exercise. Thus, individuals using inhaled human insulin via the AERx iDMS can adjust their meal-related insulin dose in connection with increased physical activity as usual. If increasing physical activity early after inhalation of insulin, the person should be aware that the maximal effect that might come earlier than usual. Until the person is aware of his/her response to inhaled insulin in relation to increased physical activity, increased caution and glucose monitoring are warranted in connection with exercise.
This study was supported by the Ministry of Science Technology and Innovation, Denmark, and sponsored by Novo Nordisk.
Published ahead of print at http://care.diabetesjournals.org on 9 July 2007. DOI: 10.2337/dc06-2589. At the time of study, A.H.P. was affiliated with the Medical University Graz, Graz, Austria. A.H.P., P.C., O.K.J., and T.S. are employed by and hold stock in Novo Nordisk. T.L., P.W., and T.R.P. have served on an advisory panel for, have received honoraria from, and have received grant/research support from Novo Nordisk. A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Received for publication January 9, 2007. Accepted for publication June 20, 2007.
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||