Subcutaneous glucose concentration in humans. Real estimation and continuous monitoring.

OBJECTIVE: To determine the real subcutaneous glucose concentration in healthy volunteers to help in the development of new calibration methods for subcutaneous glucosensors. RESEARCH DESIGN AND METHODS: We developed a new method to estimate the real subcutaneous glucose concentration based on the recirculation of phosphate-buffered saline (PBS) in a microdialysis probe inserted into the subcutaneous tissue. Tissue glucose diffuses into the probe until complete equilibration between the glucose concentration outside and inside the microdialysis probe is achieved. Later, the glucose content of the recirculated PBS is assessed in vitro. We applied the method in 10 healthy volunteers under fasting state and during a hyperglycemic clamp. In addition, we monitored the subcutaneous glucose with an enzymatic-amperometric glucosensor combined with a microdialysis probe. RESULTS: The subcutaneous glucose concentration measured by the recirculation method was 72 +/- 6 and 78 +/- 6% of the blood glucose measured in the fasting state and during the hyperglycemic clamps, respectively. On the other hand, the glucosensor's signal correlated significantly with the blood glucose. CONCLUSION: The recirculation method estimated the real subcutaneous glucose concentration, opening the way to develop new calibration procedures for subcutaneous glucosensors. However, a suitable calibration procedure is still lacking.

On line continuous monitoring of blood lactate in men by a wearable device based upon an enzymatic amperometric lactate sensor.

A wearable device for the continuous measurement of lactate in the blood was constructed by the combination of continuous blood sampling employing a double lumen catheter with an amperometric lactate sensor. In vitro, the lactate sensor turned out to have a linear concentration range between 0 and 15 mmol/l. The response time of the sensor itself amounted to 100 sec, whereas the lag time for blood sampling amounted to 2.2 min. In vivo, the lactate sensor was successfully used for the detection of changes of the blood lactate concentration following strenuous exercise in 7 healthy volunteers, in two cases up to 22 h. In conclusion, the technique of continuous blood sampling by the use of a double lumen catheter in combination with the amperometric lactate sensor is feasible and simplifies frequent blood lactate estimations.

Lack of effect of repeated administration of levetiracetam on the pharmacodynamic and pharmacokinetic profiles of warfarin.

The objective of this study was to determine if repeated administration of levetiracetam alters the pharmacokinetics or the pharmacodynamics of warfarin. Forty-two healthy subjects (18-50 years old) were recruited into the study. After a dose-finding phase and a stabilization phase, during which a warfarin treatment was introduced and the dose maintained stable for at least 5 days, 18 male and 8 female subjects were eligible and enrolled. Subjects received warfarin (2.5, 5 or 7.5 mg/day) plus levetiracetam 1000 mg bid, and warfarin plus placebo. The treatment periods were 7 days long and were separated by a 3-day wash-out period. The protein binding and the pharmacokinetic profiles of R- and S-warfarin were assessed at steady state by analysis of blood samples, and the anticoagulant effect was measured using the international normalized ratio (INR). The ratios of the geometric means for AUC(ss) (90% confidence interval) between coadministration of warfarin with levetiracetam or with placebo were 97.17% (92.85%, 101.68%) for R-warfarin and 100.16% (96.43%, 104.02%) for S-warfarin. Results for C(max), C(min) and oral clearance were consistent with those of AUC(ss). In addition, the protein binding of warfarin was not affected by the concomitant treatment. The INR values measured the last 5 days of each period were not statistically altered by the concomitant administration of levetiracetam or placebo: 1.59+/-0.18 for warfarin alone, 1.49+/-0.21 when coadministered with placebo, and 1.55+/-0.23 with levetiracetam (means+/-S.D.). The frequency and profile of adverse events under the concomitant therapy of warfarin and levetiracetam were expected for subjects receiving these drugs, and the coadministration was safe. Moreover, levetiracetam pharmacokinetics after repeated warfarin administration did not differ from those previously reported in healthy volunteers. At the doses administered, there is no evidence of a pharmacokinetic or pharmacodynamic interaction between warfarin and levetiracetam.

Long-term experiences with a computerized diabetes management and glucose monitoring system in insulin-dependent diabetic patients.

Only a minority of patients use diabetes management systems. In our study, 24 patients were given a memory based blood glucometer (ROMEO, Diva Medical Systems), which additionally allowed the input of insulin doses, food intake and exercise for up to four years. Eight patients returned ROMEO within one month (group I), 8 used the system as long it was available as a loan (group II) and 8 patients bought the system (group III). The patients of group III had a significantly better diabetic control (HbA1 = 7.8% +/- 0.7 (S.D.) vs. 11.7 +/- 3.6 (group I) and 10.7 +/- 2.6 (group II)) and were more reliable in their input of the data. After 3 years, however, only five patients of group III continued to use the system, but as a glucose meter only. One patient used the options of the system. These data show that glycemic control is not a question of the equipment. After a certain period, even the well-motivated patients do not use the system options routinely. Obviously, the advantages of the system are only used by a minority of patients characterized by good metabolic control and good compliance, and even these patients do not persistingly use all the options of the system after a certain period of time.

Differential effects of dopamine on glucoregulatory hormones in rats.

The effect of dopamine at different doses on serum concentrations of insulin, glucose and corticosterone and on plasma glucagon concentration was investigated in rats. Dopamine was given intravenously over 6 h with infusion rates of 2.5, 7.5, 15, and 60 micrograms/kg.min and in combination with phentolamine. Serum insulin concentration was unchanged at low doses of dopamine. It was significantly increased from 6.0 +/- 0.7 ng/ml to 13.7 +/- 2.3 ng/ml (P less than 0.01) when 7.5 micrograms/kg.min of dopamine were used, whereas it was significantly depressed to 3.96 +/- 0.89 and to 4.0 +/- 0.34 ng/ml (P less than 0.01), respectively, at the high doses of dopamine. This latter effect could be reversed to 6.7 +/- 1.19 ng/ml and inverted to 9.2 +/- 1.7 ng/ml (P less than 0.01) by simultaneously applied phentolamine at appropriate dosages. Serum glucose levels were markedly elevated from 154 +/- 7 to 234 +/- 42 mg/dl (P less than 0.01) by the higher doses of dopamine. A significant alteration of glucagon plasma concentrations from 18.9 +/- 2.8 to 42.3 +/- 14 pg/ml (P less than 0.01) was elicited only by 7.5 micrograms/kg.min of dopamine. The data clearly demonstrate that exogenous dopamine acts differently on glucose homeostasis according to the dosage. The study provides strong evidence that dopamine decreases insulin levels via alpha-adrenergic receptor stimulation. This effect may contribute to the deterioration of glucose homeostasis with high doses of dopamine.

Absorption and disposition of levocetirizine, the eutomer of cetirizine, administered alone or as cetirizine to healthy volunteers.

The primary objective of the present study was to compare the absorption and disposition of levocetirizine, the eutomer of cetirizine, when administered alone (10 mg) or in presence of the distomer. An additional objective was also to investigate the configurational stability of levocetirizine in vivo in humans. The study was performed in a randomized, two-way cross-over, single-dose design with a wash-out phase of 7 days between the two periods. A total of 12 healthy male and 12 healthy female volunteers were included in the study. Bioequivalence can be concluded from the analysis of the pharmacokinetic parameters of levocetirizine when administered alone or as the racemate cetirizine. No chiral inversion occurs in humans when levocetirizine is administered, i.e. there is no formation of the distomer. When comparing the pharmacokinetic characteristics of levocetirizine and the distomer, the apparent volume of distribution of the eutomer is significantly smaller than that of the distomer (0.41 and 0.60 L/kg, respectively). For an H1-antagonist a small distribution volume can be considered as a positive aspect, both in terms of efficacy and safety. Moreover the non-renal clearance of levocetirizine is also significantly lower than that of the distomer (9.70 and 28.70 mL/min, respectively), which constitutes an additional positive aspect particularly as far as metabolism-based drug interactions are concerned. The information collected in the present study on the pharmacokinetics of levocetirizine and the distomer provide additional reasons for eliminating the distomer and developing levocetirizine as an improvement on cetirizine.

Use of the microdialysis technique in the monitoring of subcutaneous tissue glucose concentration.

For some time the subcutaneous (s.c.) tissue has been the target for continuous glucose measurement. The microdialysis technique permits an extracellular region approach, which has been used for about two decades for measuring various metabolites in dialysates obtained from different body regions. By connecting a s.c. implanted microdialysis probe to a flow chamber of an amperometric glucose sensor, the procedure of glucose sensing was transferred to ex vivo. Using this device it was possible to obtain, for up to 24 hours, s.c. tissue glucose profiles of healthy and diabetic people. The microdialysis theory, the calibration process and other microdialysis technique applications are discussed in this paper. Although the combination of the microdialysis technique and amperometric glucose sensing requires certain technical equipment, the combination of microdialysis and glucose sensor seems to be a promising approach to a continuously functioning glucose sensing system.

Quality control of intensified insulin therapy: HbA1 versus blood glucose.

Since the measurement of HbA1 has become available to the diabetologists, the physicians and patients tend to rely exclusively on this parameter for the assessment of metabolic control. Therefore, in this study, 24 hour glucose profiles of 8 selected patients (4 under intensified conventional therapy, ICT, and 4 under continuous subcutaneous insulin infusion, CSII) with HbA1 values indicating good metabolic control were taken three times at four week intervals and were compared to mean blood glucose (MBG), mean average of glucose excursions (MAGE) and Schlichtkrull's M-value. MBG of the 24 profiles was 114 +/- 21 mg/dl. The patients under CSII were somewhat lower than the patients under ICT. In 16 of the 24 profiles, there was at least one period of hypoglycemia of 50 mg/dl and below. Only in one patient, M-value and MAGE showed stable metabolic control. In conclusion, hyperglycemic excursions in patients under intensified conventional therapy or treated by continuous subcutaneous insulin infusion do escape their reflection in the HbA1 values because of low blood sugar periods following hyperglycemic swings. Undoubtedly, the partial failure of ICT and CSII to prevent diabetic complications might be ascribed to the incomplete assessment of the metabolic control based on HbA1 values exclusively.

On line continuous monitoring of subcutaneous tissue glucose in men by combining portable glucosensor with microdialysis.

For the normalisation of blood glucose levels in diabetic patients by feedback controlled insulin delivery, a self-manageable and reliable method for continuous glucose estimation is still not available. By combining a commercially available needle type dialysis probe (molecular cutoff 20,000 Da) with a sensitive glucose sensor, we obtained a device for continuous glucose measurement in dialysate. This device was tested in healthy volunteers during a 75-g oral glucose tolerance test and in Type 2 (non-insulin-dependent) diabetic patients. Venous glucose and subcutaneous sensor signal were followed for 300 min (ten healthy subjects), 21 h (three healthy subjects) or 9 h (seven Type 2 diabetic patients). The recovery of the microdialysis was interindividually different, but after calibration, glucose levels in the dialysate and subcutaneous glucose sensor signal correlated well (r = 0.84-0.95). Under the assumption of a physiologic and technical delay between intravenous and subcutaneous glucose, correlation coefficient between intravenous glucose and subcutaneous sensor signal ranged from 0.60 to 0.93. We conclude that changes in blood glucose could be monitored in the subcutaneous tissue by the microdialysis technique in a continuous on line manner.

Combination of microdialysis and glucosensor permits continuous (on line) SC glucose monitoring in a patient operated device. II. Evaluation in animals.

The microdialysis technique was used for following the glucose content of the extracellular subcutaneous (SC) fluid under varying blood glucose levels in rats. The glucose content in the microdialysis perfusion fluid was continuously analyzed by means of the measuring flow chamber of an ex vivo glucose monitor. In six ChBB rats blood glucose levels were varied between 40 mg/dl and 575 mg/dl by intravenous (IV) infusion of glucose and by SC injections of insulin, respectively. After a running-in period of about half an hour, the glucose content in the perfusion fluid was closely related to the blood glucose concentration (r > 0.92) up to a time period of 6 hrs. The "relative recovery" rate of glucose by the microdialysis probe in the SC tissue varied within the 6 experimental sessions. The relative recovery rate could be shown to be not dependent on the absolute blood glucose levels in the individual rat within the glucose concentration range tested.

Combination of microdialysis and Glucosensor permits continuous (on line) s.c. glucose monitoring in a patient operated device: I. In vitro evaluation.

A device for continuous glucose monitoring in fluids was obtained by combining the microdialysis technique with a measuring flow chamber of the "Glucosensor Unitec Ulm" using the GOD method for determining amperometrically blood glucose profiles. The in vitro experiments demonstrate that the relative recovery of glucose by this device is inversely related to the flow rate of the microdialysis perfusion fluid, which, in turn, is inversely related to the response time of the device. The glucose signal increases linearly with the area of the microdialysis working membrane (r = 0.98), and with the glucose concentrations of the standard solutions (r greater than 0.95). The variation coefficient for repeated measurements is below 8%. The accuracy of the device as demonstrated by mean measuring deviation ranges between 1 and 3.8%.

Combination of microdialysis and glucose sensor for continuous on line measurement of the subcutaneous glucose concentration: theory and practical application.

The microdialysis technique can be used to get dialysates of the subcutaneous tissue, which can be continuously measured by an amperometric glucose sensor. In order to get further insight into the microdialysis procedure, we used a steady-state theory for microdialysis to predict the recovery of glucose in the dialysate and compared the results to experimental data obtained by a combination of the microdialysis technique with continuous amperometric glucose sensing. The recovery of glucose obtained in vitro for two different microdialysis probes was close to the theoretical predictions. When quantifying the predictions of the model with regard to the spatial concentration profile in the subcutaneous tissue, it appeared, that the presence of the microdialysis probe depressed the concentration of glucose for 0.2 mm from the probe surface. In a 24 hour in vivo experiment, there were less fluctuations in the sensor signal when the patient was lying in bed compared to the time, when the patient could move freely. In conclusion, the combination of microdialysis and glucose sensor seems to be a promising approach to a continuously functioning glucose sensing system. However, the microdialysis procedure itself disturbs the surrounding of the probe leading to a concentration gradient of glucose. This might explain some differences between the course of blood glucose and the course of subcutaneous glucose, measured by the combination of microdialysis and an amperometric glucose sensor. Further developments of such systems should aim at implanting microdialysis devices which have a minimal influence upon the tissue metabolism.

On line continuous monitoring of subcutaneous tissue glucose is feasible by combining portable glucosensor with microdialysis.

A new method for continuous measurement of subcutaneous tissue glucose content is introduced: by combining the microdialysis technique with a wearable amperometric glucose sensor, a device for continuous glucose measurement in the subcutaneous tissue was obtained. This device was applied to healthy volunteers (n = 10) over the period of an oral glucose load and to type I diabetic patients (n = 10) under the conditions of daily life. Glucose profiles in both healthy and diabetic persons were followed in the subcutaneous tissue up to 27 hours. This technique will certainly open new perspectives of monitoring and treating diabetic patients.

Glucoregulation under beta-adrenergic stimulation by dobutamine and terbutaline in the male rat.

The influence of the beta-adrenoreceptor stimulating agents dobutamine and terbutaline as compared to epinephrine on insulin and glucose levels has been assessed in the male rat. All agents were infused either intravenously or subcutaneously over 6 h at varying dosages. In addition, epinephrine was given concomitantly with the alpha-adrenoreceptor blocker phentolamine. The heart frequency as an estimate of the effects of the adrenergic agents beyond the glucoregulatory system was accelerated in a dose-dependent manner. Serum insulin concentrations were significantly increased by phentolamine and significantly depressed by epinephrine, while they were virtually unchanged at any dosages of dobutamine, terbutaline, or epinephrine, when simultaneously applicated with phentolamine. As for serum glucose levels, these agents, again, did not exert any influence, while glucose levels were significantly depressed under phentolamine and significantly increased under epinephrine application. The data demonstrate, that dobutamine and terbutaline at pharmacologically common dosages do not affect glucose homoeostasis. The study does not support a major effect of beta-adrenergic stimulation on the pancreatic B cell in the male rat.

Calibration problems of subcutaneous glucosensors when applied "in-situ" in man.

Continuous glucose monitoring is the conditio sine qua non to achieve total automation in glucose-controlled insulin-delivery. Several types of glucosensors have been designed according to the enzyme-amperometric method to measure the glucose in different human compartments. However, problems such as long-term stability and calibration prevent this technique being put into practice. A feasible method is needed to calibrate the glucosensor and at the same time should be accepted by the patients. To achieve calibration we determined the absolute tissue glucose, as well as the microdialysis recovery in-vivo, in healthy subjects under normal conditions and during a hyperglycaemic clamp by applying a device based on the recirculation of phosphate buffer saline in a microdialysis probe implanted in the s.c. adipose tissue. The first experiments carried out were promising and encouraging, but further investigations are still needed to favour an ideal "before implantation, all in-vitro" method to calibrate a s.c. glucosensor.

Safety, tolerability and pharmacokinetics of the new long-acting quinolone DW-116 after single and multiple dosing in healthy subjects.

The safety, tolerability and pharmacokinetics of DW-116, a new fluoroquinolone with a broad antibacterial spectrum, were evaluated in healthy male subjects after administration of single oral doses of 100, 200, 300 and 800 mg and after administration of multiple oral doses of 300 or 400 mg, respectively, for 7 days. DW-116 was well tolerated. Gastrointestinal symptoms and skin reactions were noted and considered to be possibly related to DW-116. The geometric means of the maximum plasma concentrations (Cmax) linearly increased with the dose administered from 1.19 mg/L to 8.73 mg/L after single dose administration. At steady state, the geometric mean minimum and maximum plasma concentrations were 2.14 and 5.65 mg/L, respectively, after the multiple 300 mg dose and 2.73 and 8.00 mg/L, respectively, for the multiple 400 mg dose. Tmax varied between 1 and 5 h. The terminal half-life ranged from 11.37 to 24.89 h. The geometric mean renal clearance was approximately 30 mL/min. Approximately 45% of the dose was excreted unchanged in urine within 60 h. There was no clinically relevant deviation from dose proportionality. The changes in steady-state pharmacokinetic parameters when DW-116 was taken before a high-fat breakfast were not clinically relevant. In conclusion, DW-116 was safe in this study, the first administration to human subjects. Its pharmacokinetics indicate that once-daily dosing may be possible.