Pharmacokinetic-pharmacodynamic relationships of oral hypoglycaemic agents. An update

The Mechanism of Action of Biguanides: New Answers to a Complex Question

Biguanides are a family of antidiabetic drugs with documented anticancer properties in preclinical and clinical settings. Despite intensive investigation, how they exert their therapeutic effects is still debated. Many studies support the hypothesis that biguanides inhibit mitochondrial complex I, inducing energy stress and activating compensatory responses mediated by energy sensors. However, a major concern related to this “complex” model is that the therapeutic concentrations of biguanides found in the blood and tissues are much lower than the doses required to inhibit complex I, suggesting the involvement of additional mechanisms. This comprehensive review illustrates the current knowledge of pharmacokinetics, receptors, sensors, intracellular alterations, and the mechanism of action of biguanides in diabetes and cancer. The conditions of usage and variables affecting the response to these drugs, the effect on the immune system and microbiota, as well as the results from the most relevant clinical trials in cancer are also discussed.

Continuous adsorptive removal of glimepiride using multi-walled carbon nanotubes in fixed-bed column

Water pollution by emerging pollutants such as pharmaceutical and personal care products is one of today's biggest challenges. The presence of these emerging contaminants in water has raised increasing concern due to their frequent appearance and persistence in the aquatic ecosystem and threat to health and safety. The antidiabetic drug glimepiride, GPD, is among these compounds, and it possesses adverse effects on human health if not carefully administered. Several conventional processes were proposed for the elimination of these persistent contaminants, and adsorption is among them. Therefore, in this study, the adsorptive removal of GPD from water using multi-walled carbon nanotubes (MWCNT) supported on silica was explored on a fixed-bed column. The effects of bed-height, solution pH, and flow rate on the adsorptive removal of GPD were investigated. The obtained adsorption parameters using Sips, Langmuir, and Freundlich models were used to investigate the continuous adsorption. The results showed that the drug removal is improved with the increasing bed height; however, it decreased with the flow rate. The effect of pH indicated that the adsorption is significantly affected and increased in acidic medium. The convection-dispersion model coupled with Freundlich isotherm was developed and used to describe the adsorption breakthrough curves. The maximum adsorption capacity (q_m) was 275.3 mg/g, and the axial dispersion coefficients were ranged between 3.5 and 9.0 × 10⁵ m²/s. The spent adsorbent was successfully regenerated at high pH by flushing with NaOH.

CYP2C93 variant is associated with antidiabetes efficacy of gliclazide in Chinese type 2 diabetes patients

Aims/Introduction

The objective of the present study was to investigate the effects of CYP2C9*3 polymorphisms on the therapeutic response to gliclazide in type 2 diabetes patients.

Materials and Methods

A total of 746 incident type 2 diabetes patients were included in this study. After enrolment, patients went on 4‐week gliclazide monotherapy. Fasting plasma glucose was measured before and after treatment. Hypoglycemia episodes and lifestyle information were collected by weekly follow up. Genotyping of rs1057910 was carried out using the single base primer extension method. The t‐test, analysis of variance and chisquare‐test were used to evaluate the effects of rs1057910 alleles on the therapeutic response to gliclazide.

Results

After the therapy, fasting plasma glucose decreased significantly from 11.2 ± 2.7 mmol/L to 8.0 ± 2.2 mmol/L (P < 0.001). Patients with AC/CC genotypes of rs1057910 had a greater reduction of fasting plasma glucose (3.6 vs 3.0 mmol/L, P < 0.001; 31.4 vs 24.5%, P < 0.001) and a higher rate of treatment success (54.7 vs 37.5%, P < 0.001; 51.4 vs 32.3%, P < 0.001; 71.6 vs 48.3%, P < 0.001 for criterion 1, 2 and 3, respectively).

Conclusions

The present study showed that the polymorphism at rs1057910 significantly affected the therapeutic response of gliclazide in type 2 diabetes mellitus patients. The risk allele is associated with a greater decrease of fasting blood glucose and a higher rate of treatment success with gliclazide monotherapy.

This study demonstrated that polymorphism at rs1057910 significantly affected therapeutic response of gliclazide in type 2 diabetes mellitus patients. It associated with the decrease of FPG and the rate of treatment success in the gliclazide monotherapy.

Hypoglycemia Secondary to Sulfonylurea Ingestion in a Patient with End Stage Renal Disease: Results from a 72-Hour Fast

Insulin, proinsulin, and C-peptide levels increase with sulfonylurea exposure but the acuity of increase has not been described in dialysis patients. We present a case of a dialysis patient who presented with hypoglycemia and was found to have accidental sulfonylurea ingestion. This is a 73-year-old man with ESRD on peritoneal dialysis, without history of diabetes, who presented with hypoglycemia. Past medical history includes multiple myeloma, congestive heart failure, and hypertension. At initial presentation, his blood glucose was 47 mg/dL, with concomitant elevations in the following: C-peptide 30.5 (nl: 0.8-3.5 ng/mL), insulin 76 (nl: 3-19 μIU/mL), and proinsulin 83.3 (nl: ≤8.0 pmol/L). During the 72-hour fast, which he completed without hypoglycemia, insulin declined to be within normal limits (to 12 μIU/mL); proinsulin (to 12.1 pmol/L) and C-peptide (to 7.2 ng/mL) levels decreased but remained elevated. The sulfonylurea screen ultimately returned positive for glipizide, clinching the diagnosis. This is the first reported case which characterizes the chronic elevation of proinsulin in a patient with ESRD, as well as its dramatic increase after a presumed solitary exposure to sulfonylurea. The 72-hour fast conducted gives insight into the clearance of insulin, proinsulin, and C-peptide after sulfonylurea ingestion in ESRD.

[Advances in the prevention, diagnosis and therapy of vascular diseases]

Atherosclerosis is a systemic disease affecting the coronary, carotid, intracerebral, renal and peripherial arteries. The early morphological and functional impairments could be detected in the second or third decades of life and their progression depend on the number and severity of risk factors and individual susceptility. Although the vascular risk factors (smoking, overweight, age, unhealthy diet, lack of physical exercise, hypertension, diabetes mellitus, chronic kidney disease and dyslipidemia) are the same and common in the different vascular diseases, the present clinical routine artificially classifies the diagnosis and therapy of different vascular diseases into different subfields of medicine with the negative impact of possible polypragmasia. Recently, worldwide health surveys (e.g. REACH registry) have proven the usefulness of a holistic approach in the diagnosis and therapy of multiorgan-affected vascular patients. This review summarizes the multidisciplinary advances and future perspective of vascular diseases.

Contributions of human cytochrome P450 enzymes to glyburide metabolism

Glyburide (GLB) is a widely used oral sulfonylurea for the treatment of gestational diabetes. The therapeutic use of GLB is often complicated by a substantial inter-individual variability in the pharmacokinetics and pharmacodynamics of the drug in human populations, which might be caused by inter-individual variations in factors such as GLB metabolism. Therefore, there has been a continued interest in identifying human cytochrome P450 (CYP) isoforms that play a major role in the metabolism of GLB. However, contrasting data are available in the present literature in this regard. The present study systematically investigated the contributions of various human CYP isoforms (CYP3A4, CYP3A5, CYP2C8, CYP2C9 and CYP2C19) to in vitro metabolism of GLB. GLB depletion and metabolite formation in human liver microsomes were most significantly inhibited by the CYP3A inhibitor ketoconazole compared with the inhibitors of other CYP isoforms. Furthermore, multiple correlation analysis between GLB depletion and individual CYP activities was performed, demonstrating a significant correlation between GLB depletion and the CYP3A probe activity in 16 individual human liver microsomal preparations, but not between GLB depletion and the CYP2C19, CYP2C8 or CYP2C9 probe activity. By using recombinant supersomes overexpressing individual human CYP isoforms, it was found that GLB could be depleted by all the enzymes tested; however, the intrinsic clearance (V(max)/K(m)) of CYP3A4 for GLB depletion was 4-17 times greater than that of other CYP isoforms. These results confirm that human CYP3A4 is the major enzyme involved in the in vitro metabolism of GLB.

Sulfonylurea pharmacogenomics in Type 2 diabetes: the influence of drug target and diabetes risk polymorphisms

The sulfonylureas stimulate insulin release from pancreatic beta cells, and have been a cornerstone of Type 2 diabetes pharmacotherapy for over 50 years. Although sulfonylureas are effective antihyperglycemic agents, interindividual variability exists in drug response (i.e., pharmacodynamics), disposition (i.e., pharmacokinetics) and adverse effects. The field of pharmacogenomics has been applied to sulfonylurea clinical studies in order to elucidate the genetic underpinnings of this response variability. Historically, most studies have sought to determine the influence of polymorphisms in drug-metabolizing enzyme genes on sulfonylurea pharmacokinetics in humans. More recently, polymorphisms in sulfonylurea drug target genes and diabetes risk genes have been implicated as important determinants of sulfonylurea pharmacodynamics in patients with Type 2 diabetes. As such, the purpose of this review is to discuss sulfonylurea pharmacogenomics in the setting of Type 2 diabetes, specifically focusing on polymorphisms in drug target and diabetes risk genes, and their relationship with interindividual variability in sulfonylurea response and adverse effects.

A site-specific controlled-release system for metformin

Oral absorption of the antihyperglycaemic agent metformin hydrochloride (MF-HCl) is confined to the upper part of the intestine, therefore rational controlled-release formulations of this drug should ensure a complete release during transit from stomach to jejunum. The aim of this study was the preparation of a system able to sustain release of high MF-HCl doses in compliance with the above requirement. Matrices (6 mm diameter; 50 mg weight) comprising varying drug-Precirol ATO 5 ratios were prepared by compression. The matrix containing 70% drug was coated on one face with Eudragit L100–55. Drug release to simulated gastric (SGF), jejunal (SJF) and ileal (SIF) fluids in sequence was studied using a modified USP rotating basket method. Release depended on drug load whereas it was independent of dissolution medium pH and hydrodynamics. Release kinetics were of √t type and were determined by drug diffusion in aqueous pores created in the matrix by drug dissolution. An equation correlating rate-determining factors was developed, whereby the release pattern could be optimized. The half-coated matrix started release in SGF and completed it in SJF. The half-coated matrix, synchronizing drug release and matrix transit across the small intestine, may improve drug bioavailability and reduce side effects.

A cardiologic approach to non-insulin antidiabetic pharmacotherapy in patients with heart disease

Classical non-insulin antihyperglycemic drugs currently approved for the treatment of type 2 diabetes mellitus (T2DM) comprise five groups: biguanides, sulfonylureas, meglitinides, glitazones and alpha-glucosidase inhibitors. Novel compounds are represented by the incretin mimetic drugs like glucagon like peptide-1 (GLP-1), the dipeptidyl peptidase 4 (DPP-4) inhibitors, dual peroxisome proliferator-activated receptors (PPAR) agonists (glitazars) and amylin mimetic drugs. We review the cardiovascular effects of these drugs in an attempt to improve knowledge regarding their potential risks when treating T2DM in cardiac patients. Metformin may lead to lethal lactic acidosis, especially in patients with clinical conditions that predispose to this complication, such as recent myocardial infarction, heart or renal failure. Sulfonylureas exert their effect by closing the ATP-dependent potassium channels. This prevents the opening of these channels during myocardial ischemia, impeding the necessary hyperpolarization that protects the cell. The combined sulfonylurea/metformin therapy reveals additive effects on mortality in patients with coronary artery disease (CAD). Meglitinides effects are similar to those of sulfonylureas, due to their almost analogous mechanism of action. Glitazones lower leptin levels, leading to weight gain and are unsafe in NYHA class III or IV. The long-term effects of alpha-glucosidase inhibitors on morbidity and mortality rates is yet unknown. The incretin GLP-1 is associated with reductions in body weight and appears to present positive inotropic effects. DPP-4 inhibitors influences on the cardiovascular system seem to be neutral and patients do not gain weight. The future of glitazars is presently uncertain following concerns about their safety. The amylin mimetic drug paramlintide, while a satisfactory adjuvant medication in insulin-dependent diabetes, is unlikely to play a major role in the management of T2DM. Summarizing the present information it can be stated that 1. Four out the five classical oral antidiabetic drug groups present proven or potential cardiac hazards; 2. These hazards are not mere 'side effects', but biochemical phenomena which are deeply rooted in the drugs' mechanism of action; 3. Current data indicate that the combined glibenclamide/metformin therapy seems to present special risk and should be avoided in the long-term management of T2DM with proven CAD; 4. Glitazones should be avoided in patients with overt heart failure; 5, The novel incretin mimetic drugs and DPP-4 inhibitors--while usually inadequate as monotherapy--appear to be satisfactory adjuvant drugs due to the lack of known undesirable cardiovascular effects; 6. Customized antihyperglycemic pharmacological approaches should be implemented for the achievement of optimal treatment of T2DM patients with heart disease. In this context, it should be carefully taken into consideration whether the leading clinical status is CAD or heart failure.

Interindividual variability in oral antidiabetic drug disposition and response: the role of drug transporter polymorphisms

BACKGROUND

Numerous effective oral pharmacologic therapies are available to treat type 2 diabetes. However, a substantial number of patients do not achieve the expected glucose-lowering response, or may be predisposed to adverse effects, from these agents. The application of pharmacogenetics to the field of type 2 diabetes is one step towards the goal of improved pharmacotherapeutic management of this progressive disease.

METHODS

A PubMed literature search was conducted to identify clinical studies that have examined the extent to which drug-transporter gene polymorphisms influence interindividual variability in oral antidiabetic drug disposition and response in humans.

RESULTS/CONCLUSION

Available data suggest that drug transporters play an important role in the disposition of some oral antidiabetic drugs in the body, particularly the meglitinides and metformin. Moreover, polymorphisms in genes encoding drug transport proteins may alter the pharmacodynamic profile of these agents. Drug transporters, drug-metabolizing enzymes, and drug targets each play a distinct and important role in the disposition and action of many oral antidiabetic agents. Thus, future studies may need to take a pharmacogenomic (i.e., multiple gene) approach in order to comprehensively understand the extent to which genetic variation contributes to interindividual differences in oral antidiabetic drug clinical pharmacology.

Physical–chemical characterization of binary systems of metformin hydrochloride with triacetyl-β-cyclodextrin

Interaction products of metformin hydrochloride (MF.HCl), an oral anti-hyperglycaemic agent highly soluble in water, with triacetyl-beta-cyclodextrin (TAbetaCyD), a hydrophobic CyD derivative practically insoluble in water, were prepared to evaluate their suitability for the development of a sustained-release dosage form of the drug. Equimolar MF.HCl-TAbetaCyD solid compounds were obtained by different techniques, i.e., physical mixing, kneading, co-grinding, sealed-heating, and spray-drying, in order to investigate and compare their effectiveness and influence on the physical-chemical properties of the final products. Differential scanning calorimetry, X-ray powder diffractometry, Fourier transform infrared spectroscopy and scanning electron microscopy were used for the solid-state characterization of the different MF.HCl-TAbetaCyD systems, whereas their in vitro dissolution properties were determined according to the dispersed amount method. According to the results of solid-state studies, the ability of the different preparation methods to promote effective interactions between drug and CyD varied in the order: spray-drying>co-grinding>kneading>sealed-heating approximately physical mixing. The same effectiveness rank order was observed also in dissolution studies. In fact the time to dissolve 100% drug varied increased from 1 min, for pure drug, to 3, 7, 40, 120 up to 420 min for physically mixed, sealed-heated, kneaded, co-ground and spray-dried products, respectively. Thus the drug-TA(CyD products obtained by spray drying and co-grinding were selected as the best candidates for the future development of a suitable prolonged-release oral dosage form of MF.HCl.

Pharmacokinetics and pharmacodynamics of glimepiride in type 2 diabetic patients: compared effects of once- versus twice-daily dosing

To compare the pharmacokinetic and pharmacodynamic effects of glimepiride between once- and twice-daily dosing in type 2 diabetic patients. Eight Japanese type 2 diabetic patients, who had been treated with 2 mg glimepiride alone over 4 weeks (age 40-70, body mass index <or=25 kg/m2, hemoglobin A 1C<8.0%), were randomly assigned to the crossover study with glimepiride 2 mg once-daily and 1 mg twice-daily for 4 weeks for each regime. Serum concentrations of glimepiride, plasma glucose, insulin and C-peptide were measured over 24 h at the fixed time intervals on the last day of each crossover period, and HbA 1C was measured at the same day. Pharmacokinetic profiles in two regimens were different to each others; a single peak of serum glimepiride concentration was observed in once-daily, and double peaks in twice-daily dosing. Drug concentration increased immediately, and peaked at 2 h after administration irrespective of dosage. Cmax value in once-daily dose was higher than those in twice-daily doses. AUC values were not different between two regimens. Pharmacodynamic profiles for plasma glucoses, serum insulin and C-peptide showed no statistically significant differences between two regimens, and parameters were not different each other. Analyses of adverse events and laboratory data demonstrated a favorable safety profile of glimepiride. The present results suggest that glimepiride may be suitable for once-daily dosing with respect to clinical usefulness.

Gliclazide protects human islet beta-cells from apoptosis induced by intermittent high glucose

BACKGROUND

Decreased beta-cell mass, mainly due to apoptosis, is crucial for the development and progression of type 2 diabetes. Chronic exposure to high glucose levels is a probable underlying mechanism, whereas the role of oral anti-diabetic agents (sulphonylureas in particular) is still unsettled.

METHODS

To directly investigate more on such issues, we prepared isolated human islets, which were then cultured for 5 days in continuous normal glucose concentration (NG, 5.5 mmol/L) or normal and high (HG, 16.7 mmol/L) glucose levels (alternating every 24 h), with or without the addition of therapeutical concentration (10 micromol L) of gliclazide or glibenclamide.

RESULTS

Intermittent high glucose caused a significant decrease of glucose-stimulated insulin secretion, which was not further affected by either sulphonylurea. Apoptosis, as assessed by electron microscopy, was also significantly increased by alternating high glucose exposure, which was accompanied by altered mitochondria morphology and density volume, and increased concentrations of nitrotyrosine, a marker of oxidative stress. Gliclazide, but not glibenclamide, was able to significantly reduce high glucose induced apoptosis, mitochondrial alterations, and nitrotyrosine concentration increase.

CONCLUSION

Therefore, gliclazide protected human beta-cells from apoptosis induced by intermittent high glucose, and this effect was likely to be due, at least in part, to the anti-oxidant properties of the molecule.

Relative bioavailability and bioequivalence of metforphin hydrochloride extended-released and immediate-released tablets in healthy Chinese volunteers

The aim of the present study was to investigate the relative bioavailability and bioequivalence of a new tablet formulation of metformin hydrochloride with reference to a standard product in healthy Chinese adult male volunteers. Two randomized, comparative, two-way crossover studies were therefore conducted. In study 1, which was a single-dose study, 20 subjects received 1000 mg metformin hydrochloride test product extended-release (MXR) tablets followed by the same amount of metformin hydrochloride reference product immediate-release (MIR) tablets with a 7-day washout period between the two doses. In study 2, which was a multiple-dose study, 22 subjects received MXR 1000 mg/d for 9 consecutive days followed by MIR 1000 mg/d with a 14-day washout period between the doses of the test and reference product. The serum metformin concentrations were monitored using a selective and sensitive high-performance liquid chromatography (HPLC) method with ultraviolet (UV) detection. The pharmacokinetic parameters were calculated using a 3P97 program. Analysis of variance (ANOVA) of the half-life of the absorption phase (t(1/2ka)), the half-life of the elimination phase (t(1/2ke)) and the mean retention time (MRT) and the Wilcoxon Signed Rank test of T(max) for the two preparations were significantly different. A significant difference was found in the ANOVA for C(max) in the single-dose study, while this was not the case in the multiple-dose study. Two one-sided t-tests showed that there were no significant differences in the area under the concentration-time curve (AUC) values between the two formulations. The present study indicates that the test preparation was bioequivalent to the reference preparation when both MXR and MIR were investigated in healthy Chinese adult male volunteers. And on the basis of the mean AUC(0-t), AUC(0-infinity) and AUC(ss), the relative bioavailability of the MXR was found to be 107.80%, 111.89% and 110.61% respectively compared with MIR.

Pharmacogenetics, drug-metabolizing enzymes, and clinical practice

The application of pharmacogenetics holds great promise for individualized therapy. However, it has little clinical reality at present, despite many claims. The main problem is that the evidence base supporting genetic testing before therapy is weak. The pharmacology of the drugs subject to inherited variability in metabolism is often complex. Few have simple or single pathways of elimination. Some have active metabolites or enantiomers with different activities and pathways of elimination. Drug dosing is likely to be influenced only if the aggregate molar activity of all active moieties at the site of action is predictably affected by genotype or phenotype. Variation in drug concentration must be significant enough to provide "signal" over and above normal variation, and there must be a genuine concentration-effect relationship. The therapeutic index of the drug will also influence test utility. After considering all of these factors, the benefits of prospective testing need to be weighed against the costs and against other endpoints of effect. It is not surprising that few drugs satisfy these requirements. Drugs (and enzymes) for which there is a reasonable evidence base supporting genotyping or phenotyping include suxamethonium/mivacurium (butyrylcholinesterase), and azathioprine/6-mercaptopurine (thiopurine methyltransferase). Drugs for which there is a potential case for prospective testing include warfarin (CYP2C9), perhexiline (CYP2D6), and perhaps the proton pump inhibitors (CYP2C19). No other drugs have an evidence base that is sufficient to justify prospective testing at present, although some warrant further evaluation. In this review we summarize the current evidence base for pharmacogenetics in relation to drug-metabolizing enzymes.

Treatment for childhood type 2 diabetes

Urine glucose screening at school implemented in Japan is useful for detecting childhood type 2 diabetes at the early stage of the disease. Most patients detected by the screening can improve hyperglycemia and reduce overweight within one to three months by changing lifestyle with diet and exercise. For patients who are unable to alter their lifestyle and for those who have hyperglycemia despite maintaining these changes, a variety of oral hypoglycemic agents, including α-glucosidase inhibitors, sulfonylureas, glitinides, metformin, thiazolidenediones, and insulin are available. Metformin is considered to be the most effective oral agent as monotherapy for Japanese young persons with type 2 diabetes, because most of them are obese with insulin resistance. The approach to insulin therapy in patients with type 2 diabetes often differs from that most frequently used in patients with type 1 diabetes. Adjustment of the dose of insulin at each injection using sliding scales or algorithms is not required in most cases. In some cases, combination therapy with metformin and sulfonylureas or use of insulin is more effective for stabilization of blood glucose values. Therapeutic means for childhood type 2 diabetes should be variable depending on each patient's characteristics.

Effects of prolonged in vitro exposure to sulphonylureas on the function and survival of human islets

The direct effects of prolonged exposure to sulphonylureas on the function and survival of human islets are unknown. This study assessed the insulin content, glucose-stimulated insulin release, islet cell apoptosis, and mRNA expression of insulin and GLUT-1 in isolated human islets cultured in the presence of therapeutical concentrations of glimepiride (10 microM), glibenclamide (10 microM), or chlorpropamide (600 microM). Islets were prepared by collagenase digestion and density gradient purification from 18 multiorgan donors and were then exposed for 24 h to the different sulphonylureas. Insulin content decreased significantly following culture with any sulphonylurea compound. In response to an acute challenge with 3.3 and 16.7 mM glucose, insulin release from the control islets accounted for 1.9 +/- 0.5% and 4.9 +/- 1.7% of total insulin content (P<.01), respectively. Glucose responsiveness was preserved in islets precultured in the presence of glimepiride, whereas high glucose level did not elicit any significant increase of insulin secretion from islets preincubated with glibenclamide or chlorpropamide. These alterations were reverted by an additional 48-h incubation in drug-free conditions. The amount of apoptotic cells did not differ significantly among the experimental groups. Quantitative RT-PCR studies showed that, compared with the control islets, cells preincubated with glibenclamide or chlorpropamide had an increased expression of insulin mRNA, with no change in the expression of GLUT-1. In conclusion, prolonged exposure of human islets to different sulphonylureas causes different disturbances of islet cell function, with glimepiride showing milder effects, as compared with chlorpropamide and glibenclamide.

Eudragit NE30D based metformin/gliclazide extended release tablets: formulation, characterisation and in vitro release studies

Metformin/Gliclazide extended release tablets were formulated with Eudragit NE30D by wet granulation technique. Two batches were prepared in order to study influence of drug polymer ratio on the tablet formation and in vitro drug release. The formulated tablets were characterized by disintegration time, hardness, friability, thickness, weight variation, and in vitro drug release. The percentage of polymer, with respect to Metformin/Gliclazide, required to produce tablets with acceptable qualities was 9 to 13.45. The percentage of polymer below this range released the drug immediately and above this range produced granules not suitable for tablet formation. The quantity of Metformin/Gliclazide present in the tablets and the release medium were estimated by a validated HPLC method. The formulated tablets had acceptable physicochemical characters and released the drug over 6-8 h. The data obtained from in vitro release studies were fitted with various kinetic models and was found to follow Higuchi kinetics.

Investigation of the effects of grinding and co-grinding on physicochemical properties of glisentide

The purpose of the present study was to investigate the possibility of improving the dissolution properties of glisentide, a poorly water-soluble antidiabetic drug, by grinding in a high energy micromill, alone or in mixture with polyvinylpyrrolidone (PVP). Conventional and modulated differential scanning calorimetry (DSC, MDSC), thermogravimetry (TGA), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), hot-stage FT-IR thermomicroscopy and scanning electron microscopy (SEM) were used to characterize the drug solid state, whereas its dissolution rates were determined according to the dispersed amount method. The techniques utilized enabled exclusion of polymorphism phenomena as a consequence of mechanical treatment, and revealed a progressive drug amorphization during grinding. In particular, MDSC allowed a clear determination of the glass transition temperature of the amorphous drug, enabling separation of glass transition from enthalpic relaxation. The amorphous state of the ground drug was the main responsible factor for the obtained 100% dissolution efficiency increase in comparison with the untreated drug. Further significant increases in dissolution properties, directly related to the polymer content in the mixture, were obtained by co-grinding with PVP, whose presence clearly favored drug amorphization, allowing a strong reduction of time and frequency of grinding necessary for obtaining complete drug amorphization.

Tolbutamide alters glucose transport and metabolism in the embryonic mouse heart

BACKGROUND

Tolbutamide is a sulfonylurea oral hypoglycemic agent widely used for the treatment of non insulin-dependent diabetes mellitus. Tolbutamide produces dysmorphogenesis in rodent embryos and becomes concentrated in the embryonic heart after maternal oral dosing. Tolbutamide increases glucose metabolism in extra-pancreatic adult tissues, but this has not previously been examined in embryonic heart.

METHODS

CD-1 mouse embryos were exposed on GD 9.5 to tolbutamide (0, 100, 250, or 500 microg/ml) for 6, 12, or 24 hr in whole-embryo culture. Isolated hearts were evaluated for (3)H-2DG uptake and conversion of (14)C-glucose to (14)C-lactate. Glut-1, HKI, and GRP78 protein levels were determined by Western analysis, and Glut-1 mRNA was measured by RT-PCR.

RESULTS

Cardiac (3)H-2DG uptake increased after exposure to 500 microg/ml tolbutamide for 6 hr, and 100, 250, or 500 microg/ml tolbutamide for 24 hr, compared to controls. Glycolysis increased after exposure to 500 microg/ml tolbutamide for 6 or 24 hr compared to controls. Glut-1 protein levels increased in hearts exposed to 500 microg/ml tolbutamide for 12 or 24 hr, and Glut-1 mRNA increased in hearts exposed to 500 microg/ml tolbutamide for 24 hr compared to controls. HKI protein levels increased in hearts exposed to 500 microg/ml tolbutamide for 6 hr, but not 12 or 24 hr. There was no effect on GRP78 protein levels in hearts exposed to tolbutamide for 6, 12, or 24 hr.

CONCLUSIONS

Tolbutamide stimulates glucose uptake and metabolism in the embryonic heart, as occurs in adult extra-pancreatic tissues. Glut-1 and HKI, but not GRP78, are likely involved in tolbutamide-induced cardiac dysmorphogenesis.

Oral agents for the treatment of type 2 diabetes mellitus: pharmacology, toxicity, and treatment

Currently available oral agents for the treatment of type 2 diabetes mellitus include a variety of compounds from 5 different pharmacologic classes with differing mechanisms of action, adverse effect profiles, and toxicities. The oral antidiabetic drugs can be classified as either hypoglycemic agents (sulfonylureas and benzoic acid derivatives) or antihyperglycemic agents (biguanides, alpha-glucosidase inhibitors, and thiazolidinediones). In this review, a brief discussion of the pharmacology of these agents is followed by an examination of the adverse effects, drug-drug interactions, and toxicities. Finally, treatment of sulfonylurea-induced hypoglycemia is described, including general supportive care and the management of pediatric sulfonylurea ingestions. The adjunctive roles of glucagon, diazoxide, and octreotide for refractory hypoglycemia are also discussed.

Oral antidiabetic treatment in patients with coronary disease: time-related increased mortality on combined glyburide/metformin therapy over a 7.7-year follow-up

BACKGROUND

A sulfonylurea--usually glyburide--plus metformin constitute the most widely used oral antihyperglycemic combination in clinical practice. Both medications present undesirable cardiovascular effects. The issue whether the adverse effects of each of these pharmacologic agents may be additive and detrimental to the prognosis for coronary patients has not yet been specifically addressed.

HYPOTHESIS

This study was designed to examine the survival in type 2 diabetics with proven coronary artery disease (CAD) receiving a combined glyburide/metformin antihyperglycemic treatment over a long-term follow-up period.

METHODS

The study sample comprised 2,275 diabetic patients, aged 45-74 years, with proven CAD, who were screened but not included in the bezafibrate infarction prevention study. In addition, 9,047 nondiabetic patients with CAD represented a reference group. Diabetics were divided into four groups on the basis of their therapeutic regimen: diet alone (n = 990), glyburide (n = 953), metformin (n = 79), and a combination of the latter two (n = 253).

RESULTS

The diabetic groups presented similar clinical characteristics upon recruitment. Crude mortality rate after a 7.7-year follow-up was lower in nondiabetics (14 vs. 31.6%, p<0.001). Among diabetics, 720 patients died: 260 on diet (mortality 26.3%), 324 on glyburide (34%), 25 on metformin alone (31.6%), and 111 patients (43.9%) on combined treatment (p<0.000001). Time-related mortality was almost equal for patients on metformin and on combined therapy over an intermediate follow-up period of 4 years (survival rates 0.80 and 0.79, respectively). The group on combined treatment presented the worst prognosis over the long-term follow-up, with a time-related survival rate of 0.59 after 7 years, versus 0.68 and 0.70 for glyburide and metformin, respectively. After adjustment to variables for prognosis, the use of the combined treatment was associated with an increased hazard ratio (HR) for all-cause mortality of 1.53 (95% confidence interval [CI] 1.20-1.96), whereas glyburide and metformin alone yielded HR 1.22 (95% CI 1.02-1.45) and HR 1.26 (95% CI 0.81-1.96), respectively.

CONCLUSIONS

We conclude that after a 7.7-year follow-up, monotherapy with either glyburide or metformin in diabetic patients with CAD yielded a similar outcome and was associated with a modest increase in mortality. However, time-related mortality was markedly increased when a combined glyburide/metformin treatment was used.

Comparative tolerability of sulphonylureas in diabetes mellitus

The sulphonylurea drugs have been the mainstay of oral treatment for patients with diabetes mellitus since they were introduced. In general, they are well tolerated, with a low incidence of adverse effects, although there are some differences between the drugs in the incidence of hypoglycaemia. Over the years, the drugs causing the most problems with hypoglycaemia have been chlorpropamide and glibenclamide (glyburide), although this is a potential problem with all sulphonylureas because of their action on the pancreatic beta cell, stimulating insulin release. Other specific problems have been reported with chlorpropamide that occur only rarely, if at all, with other sulphonylureas. Hyponatraemia secondary to inappropriate antidiuretic hormone activity, and increased flushing following the ingestion of alcohol, have been well described. The progressive beta cell failure with time results in eventual loss of efficacy, as these agents depend on a functioning beta cell and are ineffective in the absence of insulin-producing capacity. Differences in this secondary failure rate have been reported, with chlorpropamide and gliclazide having lower failure rates than glibenclamide or glipizide. The reasons for this are unclear, but the more abnormal pattern of insulin release produced by glibenclamide may be partly responsible and, indeed, may explain the increased risk of hypoglycaemia with this agent. Previously reported increased mortality associated with tolbutamide therapy has not been substantiated, and more recent data have shown no increased mortality from sulphonylurea treatment. Indeed, benefit from glycaemic control, regardless of the agent used--insulin or sulphonylurea--was reported by the United Kingdom Prospective Diabetes Study. Nevertheless, there is still ongoing controversy in view of the experimental evidence, mainly from animal studies, of potential adverse effects on the heart from sulphonylureas, but these are difficult to extrapolate into clinical situations. Most of these studies have been carried out with glibenclamide, which makes comparison of possible risk difficult. Other cardiovascular risk factors may be modified by gliclazide, which seems unique among the sulphonylureas in this respect. Its reported haemobiological and free radical scavenging activity probably resides in the azabicyclo-octyl ring structure in the side chain. Reduced progression or improvement in retinopathy has been reported in comparative trials with other sulphonylureas, and the effect is unrelated to improvements in glycaemia. There are differences between the sulphonylureas in some adverse effects, risk of hypoglycaemia, failure rates and actions on vascular risk factors. As a group of drugs, they are very well tolerated, but differences in overall tolerability can be identified.

The biguanide compound metformin prevents desensitization of human pancreatic islets induced by high glucose

Pancreatic islet desensitization by high glucose concentrations is a temporary and reversible state of beta-cell refractoriness to glucose (and possibly other secretagogues), due to repeated or prolonged pre-exposure to increased glucose concentrations. We evaluated whether the oral antidiabetic agent metformin affects this phenomenon in isolated, human pancreatic islets, and whether the possible effects of the biguanide are influenced by the presence of a sulphonylurea, glyburide. Islets prepared from five human pancreases were incubated for 24 h in M199 culture medium containing either 5.5 or 22.2 mmol/l glucose, with or without a therapeutic concentration (2.4 microg/ml) of metformin. Then, the islets were challenged with either 3.3 mmol/l glucose, 16.7 mmol/l glucose, or 3.3 mmol/l glucose + 10 mmol/l arginine, and insulin release was measured. After incubation in the absence of metformin, the human islets exposed to 22.2 mmol/l glucose showed no significant increase in insulin release when challenged with 16.7 mmol/l glucose (confirming that hyperglycemia desensitizes pancreatic beta-cells). In the presence of metformin, the islets fully maintained the ability to significantly increase their insulin release in response to glucose, even when previously exposed to 22.2 mmol/l glucose. No major effect on arginine-induced insulin release was observed, whatever the culture conditions. The protective action of metformin was observed also when glyburide was present in the incubation medium, whereas the sulphonylurea alone did not affect insulin release from the islets previously exposed to high glucose concentrations. These in vitro results suggest that metformin can prevent the desensitization of human pancreatic islets induced by prolonged exposure to increased glucose concentrations.

Population-based modeling to demonstrate extrapancreatic effects of tolbutamide

Tolbutamide is used increasingly as an investigative tool in in vivo studies of the physiology of glucose tolerance. Its hypoglycemic effect in nondiabetic subjects is widely variable, reflecting possible variability in its pharmacokinetics, an insulinergic response, an extrapancreatic effect of the drug, or the hypoglycemic effect of insulin itself. Using population-based modeling, we have investigated the kinetics and dynamics of tolbutamide and assessed covariates in two groups of healthy subjects. The results indicate a high variability in insulinergic effect, measured by the area under of the curve of insulin (0-60 min), in response to tolbutamide injection (coefficient of variation = 29-96%). However, it appears that impaired insulin sensitivity is compensated by higher insulin secretion in response to tolbutamide. Thus the hypoglycemic effect of high insulin secretion is minimal in insulin-resistant subjects. Application of the model indicated that tolbutamide has appreciable extrapancreatic effects mediated by prolongation of the residence time of insulin in a remote effect and by enhancement of glucose effectiveness. An effect in increasing the insulin sensitivity index is also possible but could not be confirmed statistically for all groups of subjects studied. These observations may explain inconsistencies between the results of tolbutamide and insulin injection in the frequently sampled intravenous glucose tolerance test and call for further study of insulin- vs. tolbutamide-modified frequently sampled intravenous glucose tolerance tests in the assessment of the insulin sensitivity and glucose effectiveness indexes.

Non-insulin dependent diabetes in children and adolescents: the therapeutic challenge

Data are presented comparing non-insulin dependent diabetes mellitus (NIDDM) and insulin dependent diabetes mellitus (IDDM) in youth. Children and adolescents with NIDDM were predominantly Mexican-American, presented less frequently in ketoacidosis, had a greater frequency of family history of diabetes, had higher BMIs (27.4 vs 16.6 kg/m2), and had higher frequency of acanthosis nigricans (67% vs 1.2%). Logistical, social, and cultural challenges facing the physician treating children and adolescents with NIDDM are discussed, and treatment options for NIDDM in youth are briefly reviewed.

Non-insulin-dependent diabetes mellitus in childhood and adolescence

NIDDM in children and adolescents represents a heterogeneous group of disorders with different underlying pathophysiologic mechanisms. Most subtypes of NIDDM that occur in childhood are uncommon, but some, such as early onset of "classic" NIDDM, seem to be increasing in prevalence. This observed increase is thought to be caused by societal factors that lead to sedentary lifestyles and an increased prevalence of obesity. In adults, hyperglycemia frequently exists for years before a diagnosis of NIDDM is made and treatment is begun. Microvascular complications, such as retinopathy, are often already present at the time of diagnosis. Children are frequently asymptomatic at the time of diagnosis, so screening for this disorder in high-risk populations is important. Screening should be considered for children of high-risk ethnic populations with a strong family history of NIDDM with obesity or signs of hyperinsulinism, such as acanthosis nigricans. Even for children in these high-risk groups who do not yet manifest hyperglycemia, primary care providers can have an important role in encouraging lifestyle modifications that might delay or prevent onset of NIDDM.

Oral antidiabetic drug use in the elderly

Non-insulin-dependent diabetes mellitus (NIDDM) is a metabolic disease that is common in the elderly, and is characterised by insulin insufficiency and resistance. Measures such as bodyweight reduction and exercise improve the metabolic defects, but pharmacological therapy is the most frequently used and successful therapy. The sulphonylureas stimulate insulin secretion. Metformin and troglitazone increase glucose disposal and decrease hepatic glucose output without causing hypoglycaemia. Acarbose is a dietary aid that spreads the dietary carbohydrate challenge to endogenous insulin over time. These pharmacological agents, either alone or in combination, should improve blood glucose regulation in patients with NIDDM.

The effect of pH on the in-vitro dissolution of three second-generation sulphonylurea preparations: mechanism of antacid-sulphonylurea interaction

Simultaneously administered magnesium hydroxide or sodium bicarbonate can increase the rate and extent of absorption of non-micronized glibenclamide and glipizide. To clarify the mechanism of this interaction we have studied the effect of pH on the dissolution of two different formulations of glibenclamide (micronized and non-micronized) and one formulation of glipizide. One tablet of each sulphonylurea preparation was placed in a dissolution chamber containing continuously mixed dissolution medium at pH 2, pH 6 or pH 9; 5 mL of the medium was replaced every 2 min. The amount of glibenclamide dissolved from the non-micronized formulation within 2 h, was 1.2, 4.5 and 76% at pH 2, pH 6 and pH 9, respectively (P < 0.01), whereas 21, 29 and 100% was dissolved from the micronized formulation (P < 0.01). The amount of glipizide dissolved within 2 h at pH 2, pH 6 and pH 9 was 3.9, 24 and 92%, respectively (P < 0.01). We conclude that the elevated pH of the gastric contents is the most likely explanation for the interactions previously demonstrated between antacids and sulphonylureas after their concomitant ingestion.

Clinical pharmacokinetics of metformin

The biguanide metformin (dimethylbiguanide) is an oral antihyperglycaemic agent widely used in the management of non-insulin-dependent diabetes mellitus (NIDDM). Considerable renewal of interest in this drug has been observed in recent years. Metformin can be determined in biological fluids by various methods, mainly using high performance liquid chromatography, which allows pharmacokinetic studies in healthy volunteers and diabetic patients. Metformin disposition is apparently unaffected by the presence of diabetes and only slightly affected by the use of different oral formulations. Metformin has an absolute oral bioavailability of 40 to 60%, and gastrointestinal absorption is apparently complete within 6 hours of ingestion. An inverse relationship was observed between the dose ingested and the relative absorption with therapeutic doses ranging from 0.5 to 1.5 g, suggesting the involvement of an active, saturable absorption process. Metformin is rapidly distributed following absorption and does not bind to plasma proteins. No metabolites or conjugates of metformin have been identified. The absence of liver metabolism clearly differentiates the pharmacokinetics of metformin from that of other biguanides, such as phenformin. Metformin undergoes renal excretion and has a mean plasma elimination half-life after oral administration of between 4.0 and 8.7 hours. This elimination is prolonged in patients with renal impairment and correlates with creatinine clearance. There are only scarce data on the relationship between plasma metformin concentrations and metabolic effects. Therapeutic levels may be 0.5 to 1.0 mg/L in the fasting state and 1 to 2 mg/L after a meal, but monitoring has little clinical value except when lactic acidosis is suspected or present. Indeed, when lactic acidosis occurs in metformin-treated patients, early determination of the metformin plasma concentration appears to be the best criterion for assessing the involvement of the drug in this acute condition. After confirmation of the diagnosis, treatment should rapidly involve forced diuresis or haemodialysis, both of which favour rapid elimination of the drug. Although serious, lactic acidosis due to metformin is rare and may be minimised by strict adherence to prescribing guidelines and contraindications, particularly the presence of renal failure. Finally, only very few drug interactions have been described with metformin in healthy volunteers. Plasma levels may be reduced by guar gum and alpha-glucosidase inhibitors and increased by cimetidine, but no data are yet available in the diabetic population.

The effects of obesity on the pharmacokinetics and pharmacodynamics of glipizide in patients with non-insulin-dependent diabetes mellitus

The pharmacokinetics and pharmacodynamics of glipizide were evaluated in 20 patients with non-insulin-dependent diabetes mellitus (NIDDM). The group consisted of 12 obese subjects (seven women, five men; mean +/- SD age, 53.5 +/- 8.5 years; total body weight (TBW), 95.5 +/- 17.2 kg; percentage > IBW (ideal body weight), 57.8 +/- 31.7%); and eight nonobese subjects (two women, six men; age, 57.8 +/- 11.7 years; TBW, 80.8 +/- 9.9 kg; percentage > IBW, 15.6 +/- 10.3%). After a 2-week antidiabetic drug-free period, patients were started on glipizide therapy for 12 weeks. Glipizide dosages were titrated to achieve specified therapeutic goals or a maximum daily dose of 40 mg. Glipizide pharmacokinetics were assessed by serum concentrations obtained during a 24-h pharmacokinetic evaluation performed after the first 5-mg dose (SD) and after 12 weeks of chronic therapy (CD). Glipizide pharmacodynamics were evaluated with serum glucose, insulin, and C-peptide responses to Sustacal tolerance test done at baseline, after SD, and after CD. No statistically significant differences in the SD pharmacokinetic parameters (Tmax = 3.1 +/- 1.2 vs. 2.8 +/- 1.6 h; Cmax = 332.5 +/- 92.5 vs. 420.8 +/- 142 g/L; area under the curve extrapolated to infinity (AUCI) = 2,598.3 +/- 1,148 vs. 3,138.9 +/- 1,847 g/h/L; oral clearance/bioavailability (CL/F), 2.3 +/- 1.0 vs. 2.0 +/- 1.0 L/h; volume of distribution/bioavailability (V/F), 19.5 +/- 4.4 vs. 17.2 +/- 4.3 L; t1/2 = 5.0 +/- 2.3 vs. 5.2 +/- 2.0 h) were observed between the obese and nonobese groups, respectively. The pharmacokinetic parameters assessed under CD conditions were also closely matched in the two groups. No differences in glucose responses to Sustacal challenge at baseline, SD, and CD (AUC0-->4.glucose:baseline, 52.3 +/- 18.0 vs. 44.9 +/- 9.8; SD, 50.4 +/- 20.9 vs. 36.1 +/- 11.0; CD, 37.8 +/- 10.7 vs. 36.6 +/- 8.5 mM/h) were noted between the obese and nonobese groups, respectively. However, glucose concentrations increased more and decreased to a smaller extent after SD in the obese as compared to nonobese subjects. Mean fasting serum insulin and C-peptide concentrations were not statistically different between the two groups. However, obese subjects exhibited higher fasting insulin (114.0 +/- 69 vs. 68.8 +/- 52 pM) at week 12 evaluation and C-peptide concentrations (0.83 +/- 0.2 vs. 0.63 +/- 0.2 nM) after SD as compared to the nonobese group. A smaller percentage increase in C peptide in response to Sustacal challenge was observed in the obese compared to the nonobese subjects (baseline, 60 +/- 25 vs. 117 +/- 117; SD, 119 +/- 39 vs. 193 +/- 149; and CD, 97 +/- 56 vs. 163 +/- 67%). In summary, the influence of obesity on glipizide pharmacokinetics appeared to be of little clinical significance. The observed differences in pharmacodynamics require further evaluation.

Pharmacokinetics and pharmacodynamics of the hydroxymetabolite of glimepiride (Amaryl) after intravenous administration

Glimepiride is a new sulphonylurea which is eliminated by the formation of a hydroxy-metabolite (hydroxy-gli) and a carboxymetabolite (carboxy-gli). Animal studies have shown hydroxy-gli to exhibit some hypoglycaemic effects while carboxy-gli does not appear to have any pharmacological activity. Pharmacokinetic and pharmacodynamic effects of hydroxy-gli were assessed in humans. 12 healthy male volunteers received an intravenous injection of hydroxy-gli (1.5 mg) or placebo in a single blind, randomised, cross-over study. Samples were collected for up to 24 hours (blood) or 48 hours (urine) following administration of hydroxy-gli or placebo. Hydroxy-gli significantly decreased the minimum serum concentration (Cmin) of glucose by 12% and the average serum glucose concentration over the first four hours of treatment (Cavg0-4) by 9% compared with placebo (P < or = 0.05). In addition, maximum serum C-peptide concentration (Cmax) and Cavg0-4 were both increased by 7% after hydroxy-gli (p < or = 0.05). Serum insulin concentrations (Cmax and Cavg0-4) increased by 4% but the differences from placebo were not statistically significant. No adverse events were reported during the study. In conclusion, the hydroxymetabolite of glimepiride shows pharmacological activity in human subjects.

Relationship between hypoglycaemic response and plasma concentrations of BTS 67 582 in healthy volunteers

The relationships between blood glucose, plasma insulin and plasma BTS 67 582 concentrations were studied in a randomised, placebo-controlled, four-way crossover study involving 16 healthy male volunteers aged between 19 and 43 years. Single oral doses of 125, 250 and 500 mg BTS 67 582 were studied. Fasting blood samples were taken pre-dose and half-hourly for 8 h post-dose. Mean peak plasma concentrations of BTS 67 582 were 518, 1076 and 2435 ng ml-1 for doses of 125, 250 and 500 mg, respectively. Mean maximum reductions in blood glucose were 1.13, 1.59 and 1.78 mmol l-1, and mean maximum increases in plasma insulin were 26, 14 and 21 muu ml-1 for the three doses, respectively. Changes in incremental area under the curve (AUC) of blood glucose were correlated with changes in plasma BTS 67 582 AUC. The maximum reduction in blood glucose was correlated with the peak plasma BTS 67 582 concentration. No correlations between plasma insulin and plasma BTS 67 582 concentrations were observed. Anticlockwise hysteresis was evident in concentration-effect curves, but less evident following subtraction of placebo data, and was mainly due to an underlying downward trend in fasted blood glucose levels with time evident under placebo treatment. This suggests that hypoglycaemic effects were related to systemic BTS 67 582 concentrations, suggesting that active metabolites of the drug do not make a major contribution to acute hypoglycaemic effects. A log-linear model described the relationship between blood glucose and plasma BTS 67 582 concentrations for 14 of the 16 volunteers.(ABSTRACT TRUNCATED AT 250 WORDS)

Design of drugs through a consideration of drug metabolism and pharmacokinetics

Drug metabolism input to the discovery process has been to date largely on an empirical case by case basis. Considerable advances have been made, such that basic rules can be applied to the behaviour of a compound in man based on physico-chemistry and structure. This is particularly true in the area of the cytochrome P-450 enzymes, the principal enzymes involved in the primary clearance of drugs. The major human forms, CYP2D6, CYP2C9 and CYP3A4 all have distinct substrate preferences which are being catalogued and rationalised. Such understandings will not only impact on existing drugs. Since the enzymes and systems will remain the same, these understandings can be applied to the design of molecules for the targets of the future, whilst the structure activity relationships of those targets are being researched and revealed.

Effects of the biguanide class of oral hypoglycemic agents on mouse embryogenesis

The incidence of birth defects among offspring of mothers with non-insulin dependent diabetes mellitus (NIDDM) is 2-3-fold higher than among infants of non diabetics. Since mothers with NIDDM are frequently given oral hypoglycemic agents, including sulphonylureas and biguanides, to control their disease and since these agents have been associated with the occurrence of congenital malformations in humans and animals, the embryotoxic effects of the most commonly employed biguanides, metformin and phenformin, were evaluated in whole embryo culture. Neurulating mouse embryos were exposed to therapeutic concentrations (metformin 500-2,550 mg per day; phenformin 50-400 mg per day, respectively) of the compounds for 24-48 h. Concentrations of metformin in culture ranged from 0.15 to 1.8 mg/ml and phenformin from 2.5 x 10(-5) to 0.4 mg/ml. Cultures were terminated and scored for gross morphological alterations and total protein content. Metformin produced no alterations in embryonic growth and no major malformations. Approximately 10% of all embryos exposed to metformin regardless of dose, exhibited open cranial neuropores after 24 h of culture. However, this anomaly appeared to represent a delay in closure as opposed to an overt defect, since no embryos exposed to the highest concentration of the drug and cultured for 48 h showed open neural tubes. In contrast, phenformin produced dose dependent changes in incidence of malformations, protein content, and embryolethality. Malformations included neural tube closure defects, craniofacial hypoplasia, and reduction in size of the first and second visceral arches. Doses above 0.1 mg/ml produced embryolethality and all embryos were killed at the 0.4 mg/ml concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of stress on glycemic control in patients with type II diabetes during glyburide and glipizide therapy

Stress adversely affects glycemic control in patients with type II diabetes mellitus. In addition, stress reduction with relaxation techniques or medication use in the management of hyperglycemia has been recommended. This study examined the relationship of glycemic control to self-reported stress in 19 patients with type II diabetes mellitus who were randomly allocated to receive either glyburide or glipizide for 16 weeks in a double-blind crossover design. Each treatment phase was preceded by a 2-week washout period. A previously designed and validated nine-item stress questionnaire was used to assess areas such as safety, financial wellbeing, energy level, health, etc. These areas were evaluated as more/less, better/worse, or no change. The stress questionnaire, fasting blood glucose (FBG), and glycosylated hemoglobin (GHb) concentrations were completed or measured at the end of glyburide and glipizide treatment periods. By assigning a value of 1, 2, or 3 to a positive, no change, or negative response, respectively, a composite stress score was computed and compared with glycemic control as assessed by FBG and GHb. Regression analysis showed highly significant correlations (P < .05) between stress scores and FBG (r = .70) as well as GHb (r = 0.84) with glipizide therapy. No such correlation was noted with glyburide (FBG: r = 0.29; GHb: r = 0.29). These findings suggest that during glyburide treatment, in contrast to glipizide, an increase in stress was not associated with a corresponding rise in blood glucose or worsening of metabolic control.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacotherapy of Oral Hypoglycemic Agents

The use of sulfonylurea in conjunction with a diet and exercise regimen continues to be the primary treatment modality for obese type II diabetics in the United States. These agents work to lower plasma glucose by several proposed mechanisms. Pancreatic mechanisms of action improve efficiency of the islet beta cells, and extrapancreatic mechanisms of action increase peripheral insulin-receptor sensitivity. Sulfonylureas are extensively metabolized in the liver. Depending on the specific agent, renally excreted metabolites with hypoglycemic activity may be produced and pose a threat to patients with impaired renal function. Accumulation of these metabolites can result in hypoglycemia, a common adverse reaction seen with the sulfonylurea. Other adverse reactions and their prevalence, presentation, and treatment are also presented. Clinically significant drug interactions of the sulfonylurea are tabulated and discussed. Because the sulfonlyureas have equivalent efficacy to each other, proper agent selection must be based on the metabolism and excretion characteristics, adverse reaction potential, and concurrent drug profile of the patient for whom the sulfonylurea is being selected. In patients who have not achieved adequate blood glucose control, combination therapy is sometimes initiated. Sulfonylurea-sulfonylurea and various sulfonylurea-insulin regimens are discussed. The importance of diabetic patient education is reviewed, including some basic instructions pharmacists can give to diabetics. The investigation of other oral hypoglycemic agents continues. Information of selected agents undergoing clinical trials in the United States is also reviewed.

Teratogenic effects of tolbutamide on early-somite mouse embryos in vitro

The present study investigated the teratogenicity of the oral hypoglycemic agent, tolbutamide, using an in vitro approach, and evaluated the role of its main metabolic effect, hypoglycemia. Teratogenesis was evaluated by culturing early-somite mouse embryos for 24 h in serum from rats treated with tolbutamide (79-117 micrograms/ml) or normal rat serum supplemented with tolbutamide (110-152 micrograms/ml). Tolbutamide-treated serum was then supplemented with glucose to control for potential effects of hypoglycemia. Mouse embryos demonstrated high malformation rates following exposure to serum from tolbutamide-treated rats (79%) or normal rat serum supplemented with tolbutamide (85%) compared with controls (4%), and defects included cardiac, ocular, neural tube, and somite abnormalities. Overall growth was reduced in treated embryos and yolk sacs, as determined by total protein contents. Embryonic growth and malformation rates were not improved by glucose supplementation of hypoglycemic tolbutamide-treated serum. Thus, tolbutamide produces malformation in mouse embryos in vitro at concentrations comparable to those in human serum, and the effects do not appear to be mediated by hypoglycemia. The potential risk of tolbutamide on the developing embryo must be considered in the therapy of pregnant diabetic patients.

Pharmacokinetic optimisation of oral hypoglycaemic therapy

Two main classes of oral hypoglycaemic drugs, the sulphonylureas and the biguanides, are currently used in the therapy of type II, non-insulin-dependent diabetes mellitus (NIDDM). The basic pharmacokinetic properties of these agents are discussed with a view to efficient and safe treatment. Both first- and second-generation sulphonylureas are rapidly absorbed from the gastrointestinal tract. In the plasma compartment, these drugs are strongly bound to serum proteins. All sulphonylureas are metabolised in the liver, and the metabolites and the parent drugs are eliminated mainly in the urine, but also (second-generation derivatives) in the faces. Rapid- and short-acting sulphonylureas may improve early insulin release and promote better postprandial glucose control. Long-acting derivatives may ensure better control of overnight glycaemia. The elderly are at risk of developing severe sulphonylurea-induced hypoglycaemia, and in this population the agent chosen should have a short or intermediate duration of action and no active metabolites. Caution is needed when prescribing any sulphonylurea in patients receiving drugs known to affect sulphonylurea action, and in those with impaired liver and/or kidney function. The bioavailability of the biguanides ranges from 40 to 60%. Binding to plasma proteins is absent or very low. Metformin and buformin are not metabolised and are excreted in the urine; phenformin undergoes hepatic hydroxylation and is excreted in both urine and faeces. Metformin is the only agent of this class currently recommended for clinical use. The main indications of metformin treatment are NIDDM associated with obesity and/or hyperlipidaemia, and in combination with sulphonylurea both as primary treatment and when secondary failure occurs with sulphonylurea alone. Lactic acidosis may develop in patients receiving therapy with biguanides, especially in the presence of a preexisting contraindication to their use.

The effects of magnesium hydroxide on the absorption and efficacy of two glibenclamide preparations

1. The effect of magnesium hydroxide on the absorption and efficacy of two glibenclamide preparations was investigated in healthy volunteers in two separate studies, using a randomized cross-over design with two phases. 2. A single dose of magnesium hydroxide (850 mg) or water only (150 ml) was given immediately after the ingestion of a micronised (1.75 mg, seven subjects) or a non-micronised (2.5 mg, six subjects) preparation of glibenclamide. Plasma concentrations of glibenclamide, insulin and glucose were measured. 3. Magnesium hydroxide accelerated (P less than 0.05) the absorption of glibenclamide from the micronised preparation to a small extent but the extent of absorption and the insulin and glucose responses were unaltered. 4. Coadministration of magnesium hydroxide with the non-micronised glibenclamide preparation increased the area under the plasma glibenclamide concentration-time curve from 0 to 3 h, five-fold (P less than 0.05), the total area three-fold (P less than 0.05) and the peak drug concentration three-fold (P less than 0.05). The incremental insulin area from 0 to 3 h was increased 35-fold (P less than 0.05) and the maximum insulin response 10-fold (P less than 0.05) by magnesium hydroxide. 5. Concomitant ingestion of magnesium hydroxide and non-micronised glibenclamide may greatly enhance the absorption and efficacy of glibenclamide. The absorption of micronised glibenclamide appears to be only slightly influenced by magnesium hydroxide.

Differential effects of sodium bicarbonate and aluminium hydroxide on the absorption and activity of glipizide

The effects of sodium bicarbonate and aluminium hydroxide on the absorption and activity of glipizide have been studied in healthy volunteers in two randomized cross-over trials. After an overnight fast, 5 mg glipizide was given either with 150 ml water or with water containing 3.0 g sodium bicarbonate or 1.0 g aluminium hydroxide. Sodium bicarbonate significantly increased the AUC of plasma glipizide from 0 to 0.5 h, 0 to 1 h, and from 0 to 2 h (six-, four- and twofold, respectively). The time to peak concentration (tmax) fell from 2.5 h during the control phase to 1.0 h during the sodium bicarbonate phase. The absorption half-life (t1/2a), lag time and mean residence time (MRT) were also significantly decreased. No significant change in peak plasma concentration (Cmax), total AUC or elimination half-life (t1/2) was noted. The decremental plasma glucose areas from 0 to 1 h and 0 to 2 h were significantly larger (80% and 50%, respectively) than during the control phase. The maximal decrease in glucose was 50% greater during the sodium bicarbonate phase, and the time to reach it was reduced by 35 min. Aluminium hydroxide had no significant effects on the rate or extent of absorption of glipizide, and the glucose response also remained unaffected. It is concluded that the concomitant ingestion of sodium bicarbonate and glipizide may result in accelerated absorption of glipizide and an increased effect on glucose. A common dose of aluminium hydroxide did not appear to affect the absorption of glipizide.