Impaired effect of sulfonylurea following increased dosage

Effects of gliclazide dose escalation on postprandial hyperglycemia in type 2 diabetes mellitus: A prospective, open-label, case-controlled, dose-escalation study

OBJECTIVES

The aims of this study were to determine the effects of increasing doses of gliclazide on postprandial glucose excursions after a standardized breakfast and lunch, and to clarify the relationship between gliclazide dose and glucose response.

METHODS

This prospective, open-label, case-controlled, dose-escalation study was conducted at the Addington Hospital Diabetes Clinic, eThekwini/Durban, KwaZulu-Natal, South Africa. Male and female patients aged ≥18 years with type 2 diabetes mellitus (DM) and postprandial hyperglycemia (2-hour postprandial blood glucose [PPBG2 h] level, ≥11.1 mmol/L [≥200 mg/dL]) and receiving an oral hypoglycemic agent were eligible. After a 1-week washout period during which patients were asked to discontinue treatment with all oral hypoglycemic agents, baseline glycemic measurements were performed (fasting blood glucose, PPBG2 h, 6-hour postprandial blood glucose [PPBG6 h], mean blood glucose [MBG], plasma insulin, fasting serum fructosamine, and glycosylated hemoglobin). All patients subsequently received 2 weeks of oral treatment with each of 3 doses of gliclazide: 40, 80, and 160 mg/d. Glycemic parameters were measured at the end of each dosing interval. Adverse-effect monitoring included direct reporting of untoward effects to the resident medical practitioner, clinical examination, monitoring of home blood glucose records, hematology, and liver and kidney function tests. Compliance was assessed using pill counts, examination of diary entries, and patient interview.

RESULTS

Thirty-three patients were screened; 14 entered the dose-escalation phase. Thirteen patients completed the study (7 women, 6 men; mean [SD] age, 52.0 [11.1] years); 1 was withdrawn because of poor compliance. Dose escalation from 40 to 80 mg/d was associated with a significant change only in MBG (mean [SD], 11.3 [4.2] vs 10.0 [3.9] mmol/L [203.6 (75.7) vs 180.1 (70.3) mg/dL]; P<0.001). Dose escalation from 80 to 160 mg/d was associated with a significant change only in PPBG6 h (9.5 [4.2] vs 10.3 [4.1] mmol/L [171.1 (75.7) vs 185.6 (73.9) mg/dL]; P=0.018). No other significant changes in glycemic parameters between doses were found throughout the treatment period. No adverse effects were reported.

CONCLUSIONS

In this small study of gliclazide dose escalation in patients with type 2 DM and postprandial hyperglycemia, gliclazide 80 mg/d was associated with a reduction in postprandial hyperglycemia. Dose escalation from 80 to 160 mg/d was not found to be associated with additional clinical benefit. Based on these results, we recommend that gliclazide dose escalation to the maximum dose recommended by the manufacturer be guided by measures of glycemia. All doses were well tolerated.

Caring for uninsured patients with diabetes: designing and evaluating a novel chronic care model for diabetes care

BACKGROUND

Safety net urban hospitals are being overwhelmed by an increasing number of patients with diabetes, who frequently only access the health system through visits to emergency departments and urgent care clinics. It is uncertain whether the chronic care model advocated for diabetes care would be feasible and effective for managing diabetes in an acute care setting.

OBJECTIVE

Determine if redesigning the system of care for treating diabetic patients who do not have primary care doctors is feasible, acceptable to patients and effectively lowers patients' haemoglobin A1c, blood pressure and cholesterol levels.

DESIGN

Prospective single cohort study.

PATIENTS

A total of 1098 consecutive diabetic patients presenting to an urgent care clinic at an urban safety net public hospital in Chicago between October 2004 and April 2006 who had a haemoglobin A1c measured at baseline.

INTERVENTION

Adapt the chronic care model for managing diabetes to the acute care setting of an urgent care clinic to manage uninsured patients with diabetes who do not have primary care.

RESULTS

Among the 1098 patients, 833 (76%) had a repeat A1c during the 2- to 12-month follow-up period. On average, A1c values decreased by 1.5 percentage points; systolic blood pressure decreased by 9 mmHg; low-density lipoprotein cholesterol decreased 11 points; and weight decreased 2.3 pounds (all: P < 0.001). The percentage using angiotensin-converting enzyme inhibitor drugs increased from 45% to 83%; aspirin use increased from 38% to 83%; and statin use increased from 34% to 76%.

CONCLUSIONS

This novel chronic care model for diabetes care of uninsured patients without primary care doctors was feasible, acceptable and effective in increasing the quality of diabetes care and decreasing haemoglobin A1c, blood pressure, cholesterol and weight.

A small-molecule glucokinase activator lowers blood glucose in the sulfonylurea-desensitized rat

Glucokinase activators increase insulin release from pancreatic beta-cells and hepatic glucose utilization by modifying the activity of glucokinase, a key enzyme in glucose-sensing and glycemic regulation. Sulfonylureas are antihyperglycemic agents that stimulate insulin secretion via a glucose-independent mechanism that is vulnerable to secondary failure through beta-cell desensitization. The present study determined whether glucokinase activator treatment retains its glucose-lowering efficacy in male, adult, non-diabetic Sprague-Dawley rats desensitized to sulfonylurea treatment and whether glucose-lowering during chronic glucokinase activator treatment is subject to secondary failure. Animals were given food containing either glimepiride (a sulfonylurea), Compound B (3-[(1S)-2-hydroxy-1-methylethoxy]-5-[4-(methylsulfonyl)phenoxy]-N-1,3-thiazol-2-ylbenzamide, an experimental glucokinase activator), or no drug for up to 5 weeks. Food containing 0.04% of either drug produced acute (within 4-8 h) and significant (P<0.05) reductions in blood glucose to approximately 50% of control levels. Chronic treatment with either 0.01% or 0.04% glimepiride resulted in complete failure of glucose-lowering efficacy within 3 days whereas the efficacy of Compound B was sustained throughout the entire study. Glipizide, also a sulfonylurea, had no glucose-lowering effect when given by gavage (3mg/kg) to glimepiride-desensitized animals whereas Compound B retained full glucose-lowering efficacy in glimepiride-desensitized animals. Oral glucose tolerance was significantly impaired, compared with controls, in animals treated with glimepiride for two weeks but was enhanced to a small extent in animals treated with Compound B. Compound B also significantly increased pancreatic insulin content, compared with controls. These findings suggest that Compound B has sustained glucose-lowering effects in a rat model of sulfonylurea failure.

Exenatide elicits sustained glycaemic control and progressive reduction of body weight in patients with type 2 diabetes inadequately controlled by sulphonylureas with or without metformin

BACKGROUND

In two placebo-controlled 30-week trials, treatment with exenatide reduced HbA(1c) and body weight in patients with type 2 diabetes in the context of sulphonylurea (SU) or SU plus metformin (MET) as background treatment. This analysis examines the effects of 82 weeks of exenatide treatment for participants in these earlier 30-week trials.

METHODS

Data were pooled from the two pivotal trials of exenatide added to SU or SU plus MET. Both 30-week, placebo-controlled trials of 5 microg or 10 microg exenatide b.i.d. were followed by 52-week open-label, uncontrolled extension studies in which all participants received 10 microg exenatide b.i.d. and continued prior oral therapies. This interim analysis includes data for 222 patients who completed 82 weeks of exenatide treatment (61% M, age 57 +/- 10 y, weight 99 +/- 21 kg, BMI 34 +/- 6 kg/m(2), HbA(1c)8.4 +/- 1.0% [mean +/- SD]).

RESULTS

Reduction in HbA(1c) from baseline to week 30 (-0.8 +/- 0.1% and -1.0 +/- 0.1% for 5 microg b.i.d. and 10 microg b.i.d., respectively [mean +/- SE]) was sustained up to week 82 (-1.0 +/- 0.1%). Of 207 patients with baseline HbA(1c) > 7%, 44% achieved HbA(1c) < or = 7% at week 82. Reduction of body weight from baseline to week 30 (-1.4 +/- 0.3 kg and -2.1 +/- 0.3 kg for 5 microg b.i.d. and 10 microg b.i.d., respectively) was progressive up to week 82 (-4.0 +/- 0.3 kg). The most frequent adverse events were nausea and hypoglycaemia, both generally mild to moderate in intensity.

CONCLUSIONS

Exenatide added to maximally effective doses of SU or SU plus MET resulted in a sustained reduction in HbA(1c) and a progressive reduction in weight over 1 1/2 years.

Effect of genetic polymorphisms in cytochrome p450 (CYP) 2C9 and CYP2C8 on the pharmacokinetics of oral antidiabetic drugs: clinical relevance

Type 2 diabetes mellitus affects up to 8% of the adult population in Western countries. Treatment of this disease with oral antidiabetic drugs is characterised by considerable interindividual variability in pharmacokinetics, clinical efficacy and adverse effects. Genetic factors are known to contribute to individual differences in bioavailability, drug transport, metabolism and drug action. Only scarce data exist on the clinical implications of this genetic variability on adverse drug effects or clinical outcomes in patients taking oral antidiabetics. The polymorphic enzyme cytochrome P450 (CYP) 2C9 is the main enzyme catalysing the biotransformation of sulphonylureas. Total oral clearance of all studied sulphonylureas (tolbutamide, glibenclamide [glyburide], glimepiride, glipizide) was only about 20% in persons with the CYP2C9*3/*3 genotype compared with carriers of the wild-type genotype CYP2C9*1/*1, and clearance in the heterozygous carriers was between 50% and 80% of that of the wild-type genotypes. For reasons not completely known, the resulting differences in drug effects were much less pronounced. Nevertheless, CYP2C9 genotype-based dose adjustments may reduce the incidence of adverse effects. The magnitude of how doses might be adjusted can be derived from pharmacokinetic studies. The meglitinide-class drug nateglinide is metabolised by CYP2C9. According to the pharmacokinetic data, moderate dose adjustments based on CYP2C9 genotypes may help in reducing interindividual variability in the antihyperglycaemic effects of nateglinide. Repaglinide is metabolised by CYP2C8 and, according to clinical studies, CYP2C8*3 carriers had higher clearance than carriers of the wild-type genotypes; however, this was not consistent with in vitro data and therefore further studies are needed. CYP2C8*3 is closely linked with CYP2C9*2. CYP2C8 and CYP3A4 are the main enzymes catalysing biotransformation of the thiazolidinediones troglitazone and pioglitazone, whereas rosiglitazone is metabolised by CYP2C9 and CYP2C8. The biguanide metformin is not significantly metabolised but polymorphisms in the organic cation transporter (OCT) 1 and OCT2 may determine its pharmacokinetic variability. In conclusion, pharmacogenetic variability plays an important role in the pharmacokinetics of oral antidiabetic drugs; however, to date, the impact of this variability on clinical outcomes in patients is mostly unknown and prospective studies on the medical benefit of CYP genotyping are required.

Interim analysis of the effects of exenatide treatment on A1C, weight and cardiovascular risk factors over 82 weeks in 314 overweight patients with type 2 diabetes

AIM

Exenatide, an incretin mimetic for the adjunct treatment of type 2 diabetes (DM2), reduced A1C and weight in 30-week placebo-controlled trials. This analysis examined the effects of exenatide on glycaemic control and weight over an 82-week period in patients with DM2 unable to achieve adequate glycaemic control with sulphonylurea (SU) and/or metformin (MET).

METHODS

This interim analysis is of 314 patients who received exenatide in the 30-week placebo-controlled trials and subsequently in 52 weeks of open-label uncontrolled extension studies for 82 weeks of exenatide in total. Patients continued their SU and/or MET regimens throughout.

RESULTS

Patients completed 82 weeks of exenatide treatment [n = 314, 63% M, age 56 +/- 10 years, weight 99 +/- 21 kg, body mass index 34 +/- 6 kg/m2, A1C 8.3 +/- 1.0% (mean +/- SD)]. Reduction in A1C from baseline to week 30 [-0.9 +/- 0.1% (mean +/- SE)] was sustained to week 82 (-1.1 +/- 0.1%), with 48% of patients achieving A1C < or = 7% at week 82. At week 30, exenatide reduced body weight (a secondary endpoint) from baseline (-2.1 +/- 0.2 kg), with progressive reduction at week 82 (-4.4 +/- 0.3 kg). Similar results were observed for the intent-to-treat population (n = 551), with reductions in A1C and weight at week 82 of -0.8 +/- 0.1% and -3.5 +/- 0.2 kg respectively. The 82-week completer cohort showed statistically significant improvement in some cardiovascular risk factors. The most frequent adverse events were generally mild-to-moderate nausea and hypoglycaemia.

CONCLUSION

In summary, 82 weeks of adjunctive exenatide treatment in patients with DM2 treated with SU and/or MET resulted in sustained reduction in A1C and progressive reduction in weight, as well as improvement in some cardiovascular risk factors.

Kinetics-effect relations of insulin-releasing drugs in patients with type 2 diabetes: brief overview

Sulfonylureas and glinides have similar mechanisms of action but differ in receptor affinity and binding sites and in absorption and elimination rates. This promotes differences in potency, rate of onset, and duration of action. While prominent in single-dose studies, these differences have less importance during long-term sulfonylurea treatment: at ordinary dosages, rapid- and short-acting (glipizide) and slow- and long-acting (glyburide) sulfonylureas maintained continuously effective plasma levels and similar 24-h glucose control. Moreover, there was no difference in patient outcome between the first-generation sulfonylurea chlorpropamide and the second-generation glyburide in the U.K. Prospective Diabetes Study. However, the risk of long-lasting and hence dangerous hypoglycemia is higher with these two long-acting sulfonylureas. Conversely, this risk should be low with the short-acting glinides, but seemingly at the expense of less effective glucose control. The most important kinetics-effect relations are that hyperglycemia delays sulfonylurea absorption and that the sulfonylurea dose-response curve is bell shaped; continuous sulfonylurea exposure over a certain level (e.g., 10 mg glipizide) impairs rather than improves insulin and glucose responses to sulfonylurea (downregulation). Accordingly, a vicious circle may be established: unrelenting hyperglycemia may promote sulfonylurea dose increase, which increases hyperglycemia, promoting further dose increase and eventually therapeutic failure.

Practical considerations and guidelines for dosing sulfonylureas as monotherapy or combination therapy

BACKGROUND

Oral antidiabetic agents are the initial and most commonly used therapy for type 2 diabetes mellitus. To effectively utilize the oral antidiabetic agents, familiarity with the efficacy and side effects of each agent is essential so that strategies for effective therapy with 1 or more agents can be developed when transitioning is needed either with monotherapy or to combination therapy with another antidiabetic agent.

OBJECTIVES

The purposes of this article were to review the efficacy and adverse-event profile of sulfonylureas, the most widely used class of oral antidiabetic agents in the United States, and to provide a simple set of guidelines for use in transitioning patients between sulfonylureas or to combination therapy.

METHODS

A comprehensive search of the MEDLINE and PubMed databases for the years 1966 to present and a thorough review of abstracts of recently presented clinical trials were used to identify relevant literature on dosing conversion and equivalence between sulfonylureas. Search terms used were as follows: sulfonylureas, dosing conversion, equivalence, glyburide, glipizide, glimepiride, and combination therapy. Strategies are provided for switching patients between sulfonylureas so that switching within the sulfonylurea class or to a combination tablet can be accomplished efficaciously and safely. Recommendations for dosing conversion were based on the results of the literature and abstract search, manufacturer recommendations for each available agent, and the author's clinical experience.

RESULTS

When switching between agents or starting combination therapy, it is important to monitor for hypoglycemia. Fasting serum glucose levels and glycosylated hemoglobin should also be monitored to determine the optimal dose of sulfonylurea for each patient Patients not achieving adequate control on a single agent should be transferred to combination therapy.

CONCLUSION

When transferring a diabetic patient to a combination tablet, improved compliance, cost savings, and better glycemic control may be achieved.

Effects of exenatide (exendin-4) on glycemic control over 30 weeks in sulfonylurea-treated patients with type 2 diabetes

OBJECTIVE

This study evaluated the ability of the incretin mimetic exenatide (exendin-4) to improve glycemic control in patients with type 2 diabetes failing maximally effective doses of a sulfonylurea as monotherapy.

RESEARCH DESIGN AND METHODS

This was a triple-blind, placebo-controlled, 30-week study conducted at 101 sites in the U.S. After a 4-week, single-blind, placebo lead-in period, 377 subjects were randomized (60% men, age 55 +/- 11 years, BMI 33 +/- 6 kg/m(2), HbA(1c) 8.6 +/- 1.2% [+/-SD]) and began 4 weeks at 5 microg subcutaneous exenatide twice daily (before breakfast and dinner; arms A and B) or placebo. Subsequently, subjects in arm B were escalated to 10 microg b.i.d. exenatide. All subjects continued sulfonylurea therapy.

RESULTS

At week 30, HbA(1c) changes from baseline were -0.86 +/- 0.11, -0.46 +/- 0.12, and 0.12 +/- 0.09% (+/-SE) in the 10-microg, 5-microg, and placebo arms, respectively (adjusted P < 0.001). Of evaluable subjects with baseline HbA(1c) > 7% (n = 237), 41% (10 microg), 33% (5 microg), and 9% (placebo) achieved HbA(1c) <or= 7% (P < 0.001). Fasting plasma glucose concentrations decreased in the 10-microg arm compared with placebo (P < 0.05). Subjects in the exenatide arms had dose-dependent progressive weight loss, with an end-of-study loss in the 10-microg exenatide arm of -1.6 +/- 0.3 kg from baseline (P < 0.05 vs. placebo). The most frequent adverse events were generally mild or moderate and gastrointestinal in nature. No severe hypoglycemia was observed.

CONCLUSIONS

Exenatide significantly reduced HbA(1c) in patients with type 2 diabetes failing maximally effective doses of a sulfonylurea. Exenatide was generally well tolerated and was associated with weight loss.

Combination therapy with rosiglitazone and glibenclamide compared with upward titration of glibenclamide alone in patients with type 2 diabetes mellitus

AIM

To compare the efficacy of combination therapy using rosiglitazone (8 mg per day) and glibenclamide (7.5 mg per day) with upward titration of glibenclamide as monotherapy (maximum dose=15 mg per day) in reducing HbA(1c) levels over 26 weeks in patients with type 2 diabetes mellitus (T2DM).

METHODS

Three hundred and forty patients with T2DM inadequately controlled (FPG > or =7.0 and < or =15.0 mmol/l) on glibenclamide 7.5 mg per day were randomised to either additional treatment with rosiglitazone 8 mg per day or up-titration of the glibenclamide dose (maximum dose=15 mg per day).

RESULTS

After 26 weeks, treatment with rosiglitazone combination reduced HbA(1c) by 0.81% (P<0.0001) and FPG by 2.4 mmol/l (P<0.0001) compared with glibenclamide monotherapy. HOMA-S and HOMA-B increased by 12 and 28%, respectively (P<0.0001 for both) with combination compared with glibenclamide monotherapy. With rosiglitazone combination and glibenclamide monotherapy, total cholesterol: HDL ratio reduced by 5 and 13%, triglycerides reduced by 6 and 2%, and FFAs reduced by 15 and 8%, respectively. Both treatments were well tolerated and had predictable safety profiles.

CONCLUSION

For patients inadequately controlled on glibenclamide, addition of rosiglitazone provides significantly improved glycaemic control compared with uptitration of glibenclamide. This may be preferable to continued monotherapy with higher doses of glibenclamide.

Effects and serum levels of glibenclamide and its active metabolites in patients with type 2 diabetes

OBJECTIVE

To study the effects and serum levels of glibenclamide (Gb) and its active metabolites in patients on chronic Gb medication on different daily doses.

MATERIAL AND METHODS

Fifty patients with type 2 diabetes on regular Gb therapy (1.75-14.0 mg daily). Blood samples were taken immediately before and 90 min after regular Gb intake. A standardized breakfast was served 30 min after drug intake. Serum insulin and proinsulin levels were determined by ELISA methods without cross-reactivities. Serum drug levels were determined by HPLC. Fischer's R to Z-test (correlation coefficients) and paired Student t-tests were used when comparing values within the entire group and unpaired non-parametric Mann-Whitney tests were used when comparing high and low dose levels. A p-value < 0.05 was considered significant.

RESULTS

There were significant correlations between daily Gb dose, on the one hand, and, on the other, HbAlc (r = 0.55), Delta-insulin (r = - 0.59) and Delta-proinsulin (r = - 0.52) levels. Significant correlations between Gb therapy duration and insulin (r = - 0.40) and proinsulin (r = - 0.34) secretion and between Gb dose and ratio proinsulin/insulin (RPI) at both time points (r = 0.32 and 0.30) were also found. The RPI was lower after Gb intake. In patients on > or = 10.5 mg steady state serum metabolite levels (Ml and Ml + M2) were higher (29(0-120) and 33 (0-120) ng/ml) than those of Gb itself (18(0-64) ng/ml). A great inter-subject variability in Gb levels at both time points was seen.

CONCLUSIONS

Our results indicate that, in patients on chronic medication, Gb is capable of stimulating both insulin and proinsulin secretion; the effect on insulin release is relatively greater. The effect was more pronounced in patients on a low Gb dose, either because of less impaired beta-cells in those receiving low doses, or due to reduced sulphonylurea sensitivity in those on high dosage (down-regulation). In patients on a daily dose of 10.5 mg or more, serum metabolite levels of clinical relevance were demonstrated; the metabolites may contribute to hypoglycaemic events.

The NEPI antidiabetes study (NANSY). 1: short-term dose-effect relations of glimepiride in subjects with impaired fasting glucose

AIM

NANSY is a randomised, placebo-controlled Swedish-Norwegian study which aims to include 2 x 1112 male and female subjects with impaired fasting glucose (IFG), to assess whether conversion to type 2 diabetes can be delayed by addition of sulphonylurea to dietary regulation and increased exercise. This pilot study was conducted to find the optimum dose of glimepiride in NANSY.

METHODS

In a double blind trial in primary care 25 IFG subjects were in random order exposed to single doses and one-week treatments with 0 (placebo), 0.5, 1.0 and 2.0 mg glimepiride once daily. The optimum dose was assessed by measuring blood glucose during oral 75 g glucose tolerance test (OGTT), comparing fasting blood glucose, and the area under the blood glucose curve (AUC), and by monitoring hypoglycaemic events.

RESULTS

With single doses, there was a clear dose-response relationship for the reduction in AUC, with a statistically significant difference only between placebo (mean 1981, 95% confidence intervals (CI) 1883-2078) and 2 mg glimepiride (mean 1763, 95% CI 1665-1861). However, following 1-week treatments, the only significant difference was between placebo (mean 1934, 95% CI 1856-2012) and 1 mg glimepiride (mean 1714, 95% CI 1637-1792). Correspondingly, the only statistically significant difference in fasting blood glucose day 7 was between placebo (5.87 mmol/l, 95% CI 5.68-6.05 mmol/l) and 1 mg glimepiride (5.42 mmol/l, 95% CI 5.21-5.62 mmol/l). Chemical hypoglycaemia was common but hypoglycaemic symptoms were rare and similar between the active doses, and easily countered by the subjects.

CONCLUSIONS

The sulphonylurea dose-effect curve may be bell-shaped, perhaps due to down regulation of sulphonylurea receptors during chronic exposure. Alternatively, the finding could be a rebound phenomenon, secondary to preceding hypoglycaemia. The optimum dose for NANSY was found to be 1 mg glimepiride.

Differences in pharmacotherapy and in glucose control of type 2 diabetes patients in two neighbouring towns: a longitudinal population-based study

AIM

To compare prescribing, dosage and blood glucose levels in patients with type 2 diabetes in two communities with differences in anti-hyperglycaemic drug utilization.

METHODS

A retrospective longitudinal (1984-1994) population-based study in two neighbour towns in southern Sweden. The mean prescribed daily dose was expressed as a fraction of the Defined Daily Dose (DDD) for each drug.

RESULTS

In town A, prescribing of oral agents and insulin was predominantly made by one specialized diabetes clinician, while in town B it was spread among several different general practitioners and one specialist. Altogether 44 636 medical visits by 2348 patients were identified. In each town, about 40% of the patients were treated without anti-hyperglycaemic drugs, about 40% with oral agents and about 20% with insulin. However, there were pronounced between-town differences in dosage and glucose control. The mean prescribed daily dose of sulphonylurea monotherapy decreased gradually from approximately 0.7 to approximately 0.5 DDD in town B but remained approximately 0.8 DDD in town A. The proportion of patients on both sulphonylurea and metformin increased substantially in town A but not in town B. In these patients, the mean prescribed daily dose of sulphonylurea exceeded 1.0 DDD in both towns, although it decreased with time in town B. The mean prescribed daily dose of insulin increased from 1.05 to 1.2 DDD in town A but remained virtually unchanged at 0.95 DDD in town B. The mean fasting blood glucose was lower in town A than in town B both overall (7.7 vs. 8.8 mmol/l), in those treated without any anti-hyperglycaemic drugs (7.2 vs. 8.1 mmol/l), in those on sulphonylurea monotherapy (8.3 vs. 9.7 mmol/l) and in those treated with insulin (8.1 vs. 10.2 mmol/l).

CONCLUSIONS

Glucose control in routine care was better when most patients were treated by a diabetes specialist and were exposed to more intense pharmacotherapy.

[Present status in the treatment of type 2 diabetes mellitus. Insulin-secreting agents]

The functional defect of the pancreatic beta cell represents one of the main therapeutic targets in type 2 diabetes mellitus. Among the currently available oral antidiabetic drugs, only hypoglycaemic sulfonylureas exhibit beta cell stimulating properties. However, their use has some limits, particularly those related to the risk of hypoglycaemia and the frequent secondary therapeutic failure. These drugs have largely contributed to the knowledge of the mechanisms of insulin secretion. Besides some galenic modifications of existing sulfonylureas and the development of new drugs of this family with original properties, like glimepiride, the research is essentially focused on drugs derived from the non sulfonylurea moiety of some sulfonylureas, particularly the meglitinide family, which will probably be available for the clinician in the near future. These drugs act however grossly by the same mechanism than sulfonylureas, even if their binding site on a protein coupled with the ATP sensitive K channel appears different. Among the other possible approaches suggested by the theoretical data concerning the mechanisms of insulin secretion, GLP-1 derivatives probably represent good candidates, if stable analogues are developed.

Diabetic neuropathy in elderly Type 2 diabetic patients: effects of insulin treatment

OBJECTIVES

To study the occurrence of diabetic neuropathy and the effect of insulin treatment in elderly Type 2 diabetic patients.

MATERIAL AND METHODS

In 38 patients and 20 controls symptoms and neurophysiological examinations including electroneurography, vibration perception and temperature discrimination thresholds were investigated. Patients were randomized to insulin (n = 18) or sulfonylurea (n = 16) treatment and were re-investigated after 1 year.

RESULTS

Neuropathy was present in 21/38 patients (56%). It was asymptomatic in 17/38 (45%) and symptomatic in 4/38 (11%). The occurrence of neuropathy was less common in healthy controls, 3/20 (15%) (P < 0.01). Temperature discrimination thresholds was the test that most often revealed pathology. The metabolic control after 1 year was significantly improved in the insulin treated group and unchanged in the sulfonylurea treated group. There were no changes as regards occurrence of neuropathy between or within the two treatment groups after 1 year.

CONCLUSION

Diabetic neuropathy is common among elderly Type 2 diabetic patients. It is mostly asymptomatic. Improvement was not seen after 1 year of insulin treatment.

Issues surrounding tight glycemic control in people with type 2 diabetes mellitus

OBJECTIVE

To review the prospective evidence surrounding the issue of tight glycemic control in people with type 2 diabetes mellitus and resultant long-term complications.

DATA SOURCE

Conference proceedings and a MEDLINE search (1966-February 1998) identified pertinent English-language publications on type 2 diabetes in humans. Key search terms included insulin resistance, diabetes mellitus, non-insulin-dependent, macrovascular complications, microvascular complications, and intensive glycemic control.

STUDY SELECTION

Selection of prospective epidemiologic and clinical studies were limited to those focusing on the management of type 2 diabetes. All articles with pertinent information relevant to the scope of this article were reviewed.

DATA SYNTHESIS

The pathophysiology of type 1 and type 2 diabetes differ; however, both share chronic complications that significantly affect morbidity and mortality. People with type 1 diabetes have an absolute deficiency of insulin, whereas people with type 2 diabetes have varying degrees of insulin resistance and an inadequate compensatory insulin secretory response. The Diabetes Control and Complications Trial (DCCT) has clearly indicated that intense control of blood glucose in type 1 diabetes prevents and slows the progression of microvascular (i.e., retinopathy, nephropathy) and neuropathic complications. The Kumamoto study showed similar results in nonobese patients with type 2 diabetes. Intense insulin therapy in both populations has proven advantageous, thus supporting a common pathophysiologic process for the microvascular and neuropathic complications. Trends were seen toward fewer macrovascular (atherosclerotic disease) complications in the intensive insulin arm of the DCCT. Conversely, trends were seen toward an increase in macrovascular complications in the VA Cooperative study in people with type 2 diabetes using intensive insulin therapy. This may suggest a discordance in the pathophysiology of macrovascular disease between type 1 and type 2 diabetes. Additionally, it remains uncertain whether tight glycemic control prevents the onset or slows the progression of macrovascular disease. Two studies (the University Group Diabetes Program and the Veterans Affairs Cooperative Study on Glycemic Control and Complications in Type 2 Diabetes) to date have examined pharmacotherapy options for patients with type 2 diabetes and resultant macrovascular complications. It has yet to be determined whether any therapeutic intervention will decrease the morbidity and mortality of macrovascular disease in this population.

CONCLUSIONS

In type 2 diabetes, limited prospective evidence does support tight glycemic control to help prevent or slow the progression of microvascular and neuropathic complications. It is uncertain whether tight glycemic control decreases macrovascular complications and which pharmacotherapeutic agent(s) is/are the best options. However, therapy that improves glucose control in combination with aggressive risk factor management should be initiated and enforced in patients with type 2 diabetes in an effort to reduce long-term complications.

Is there a concentration-effect relationship for sulphonylureas?

Sulphonylureas have remained the mainstay of oral therapy for type 2 (non-insulin-dependent) diabetes mellitus (NIDDM). They stimulate insulin release from pancreatic beta cells. Pharmacokinetic differences between the various sulphonylureas are of clinical importance in terms of the time to onset of action, timing of drug administration in relation to food intake, magnitude and duration of the glucose-lowering effect and the risk of serious hypoglycaemia. Recent studies with improved analytical sensitivity have shown that the elimination half-life of glibenclamide is longer than previously thought and that 2 metabolites of glibenclamide have significant hypoglycaemic activity. Furthermore, single dose studies in healthy volunteers using an integrated pharmacokinetic-pharmacodynamic model have identified clear concentration-effect relationships for both glibenclamide and its metabolites after oral and intravenous administration. Under multiple dose conditions, kinetic-dynamic relations have been identified with shorter-acting drugs in dosages that give discontinuous sulphonylurea exposure. However, at continuous exposure, i.e. sustained 24-hour therapeutic concentrations in plasma, there is evidence indicating the development of tolerance, which may be caused by downregulation of beta cell sensitivity. As more sophisticated concentration-effect studies appear, it has become evident that currently recommended maximum daily doses of many sulphonylureas are too high.

Sulfonylureas

Sulfonylureas have been available for the treatment of non-insulin-dependent diabetes mellitus (NIDDM) since the 1950s. With the introduction of new oral agents, there is a tendency to discount the value of sulfonylurea therapy. Sulfonylureas have the advantage of multiple formulations, low costs, minimal side effects, and demonstrated efficacy in controlling hyperglycemia. The major disadvantage of sulfonylureas is secondary failure, which may occur with all oral agents as part of the progression of NIDDM. Sulfonylureas should continue to play an important role in the treatment of NIDDM.

Starting insulin therapy in elderly non-insulin-dependent diabetic patients at a health care centre. Methodological and economic aspects

OBJECTIVE

To try to start insulin therapy in elderly non-insulin-dependent diabetes mellitus (NIDDM) patients with secondary failure in primary health care, and compare costs for starting treatment in a health care centre and in a day-care clinic in a hospital.

DESIGN

Time and costs for start of insulin were calculated.

SETTING

A health care centre in Stockholm, Sweden.

SUBJECTS

Fourteen consecutive patients in the health care centre and a control group of 14 patients in the day-care clinic.

RESULTS

Metabolic control in both groups improved significantly. Total time spent with the district nurse to start insulin treatment was 3 hours during about 7 weeks with a total cost of SEK 1100 in the health care centre. In the day-care clinic patients were admitted 5.6 days with a total cost of SEK 6100-10900.

CONCLUSIONS

Elderly patients can learn the injection technique and manage insulin therapy, which results in good metabolic control. Insulin treatment can be started in primary health care. With elderly patients it takes time, but it is far more cost-effective in primary health care than at the hospital.

Antihyperglycaemic efficacy, response prediction and dose-response relations of treatment with metformin and sulphonylurea, alone and in primary combination

The short-term (2-12 weeks) antihyperglycaemic efficacy of metformin (M), glibenclamide (G), and their primary combination (MG) was assessed in a double-blind study including 165 unselected patients with Type 2 diabetes. Patients with diet failure were randomized to M, G or MG. The dose was titrated with a fasting blood glucose concentration (FBG) of < 6.7 mmol l-1 as the target, using at most six dose levels, the first three comprising increasing monotherapy (M or G) or low-dose primary combination (MGL), and the second three add-on therapies (M/G and G/M) and primary combination therapy escalated to high dose (MGH). Success rates were higher on MGL than on monotherapy. The difference in achieving acceptable control (FBG < or = 7.8 mmol 1(-1)) was 70% versus 51% (95% confidence interval 3-36%, p = 0.032). When the drugs were combined, a slightly greater FBG reduction (p = 0.026) was observed, at lower dosage (p = 0.013). The response could not be predicted from body weight, but depended upon initial FBG (p = 0.019) and meal-stimulated C-peptide (p = 0.007). FBG declined progressively with increasing doses of metformin, whereas glibenclamide exerted most of its effect at low dose. Primary combination therapy with metformin and sulphonylurea may be clinically useful.

Supramaximal decrease of sulphonylurea-induced accumulation of sodium in pancreatic islets

Sodium was measured in beta-cell-rich pancreatic islets of mice under steady state conditions or after 6 min of exposure to 1 mM ouabain. The islet content of sodium increased when 100 microM tolbutamide or 1 microM glipizide were added to an albumin-containing (1 mg ml-1) medium, but remained unaffected at 10-fold higher concentrations. Both sulphonylurea compounds promoted the uptake of Na+ in the presence of ouabain. Whereas tolbutamide was stimulatory at 10 microM or above in a medium containing 10 mg ml-1 albumin, only 0.1 microM was required in the absence of albumin. In the latter situation there was a reduction of the stimulatory action with increase of the tolbutamide concentration from 100 to 1000 microM. The inhibitory component in the sulphonylurea action on the Na+ uptake was particularly impressive with glipizide, maximal stimulation being reached at 10 microM in the presence of 1 mg ml-1 albumin. Diazoxide (400 microM) modified the glipizide action on Na+ uptake, making 1000 microM stimulatory instead of 1 microM. The latter concentration of glipizide became inhibitory after removal of K+. Glipizide stimulated the Na+ uptake both at low and high concentrations in a medium deficient in Ca2+ or when the cotransport of Na+, K+ and Cl- was blocked by 20 microM bumetanide. The observation that the sulphonylurea-induced islet accumulation of sodium is diminished at supramaximal concentrations reinforces existing arguments for additional effects of high concentrations of hypoglycemic sulphonylureas.

A long-term, randomized, comparative study of insulin versus sulfonylurea therapy in type 2 diabetes

OBJECTIVES

To study the effect of insulin and sulfonylurea (SU) therapy on glycaemic control, insulin resistance and cardiovascular risk factors in type 2 diabetic subjects.

DESIGN

A prospective, parallel, randomized, controlled, long-term study.

SETTING

Outpatient clinic in tertiary referral centre.

SUBJECTS

Thirty-six type 2 diabetic subjects treated with diet and SU, aged 44-69 years and a duration of diabetes of between 2 and 14 years.

INTERVENTIONS

Individually adjusted doses of insulin and glibenclamide.

MAIN OUTCOME MEASURES

Glycosylated haemoglobin (HbA1c), insulin resistance (euglycaemic glucose clamp), levels of lipids, lipoproteins and blood pressure.

RESULTS

Glycaemic control improved during insulin treatment, but deteriorated on SU; HbA1c levels differed significantly between groups after 12 months of therapy (mean +/- SEM 7.9 +/- 0.3 vs. 9.5 +/- 0.4%, P = 0.004). Body mass index increased significantly during insulin treatment (26.4 +/- 0.7 to 27.8 +/- 0.7 kg/m2, P = 0.0001) and 30% of this increase was a result of an increase in lean body mass. The total glucose disposal rate showed a small increase in the insulin group. Levels of triglycerides and apolipoprotein B were significantly reduced during insulin treatment (1.8 +/- 0.2 to 1.5 +/- 0.2 mmol L-1, P = 0.03 and 1.58 +/- 0.1 to 1.40 +/- 0.08 g L-1, P = 0.003), and insulin prevented a reduction in the levels of high-density lipoprotein (HDL) cholesterol and apolipoprotein A-1 and an increase in Lp(a) lipoprotein observed in the SU group. Blood pressure levels did not change during therapy.

CONCLUSIONS

Insulin therapy was superior to SU treatment in achieving good metabolic control. Despite a modest improvement in cardiovascular risk factors in the insulin-treated group, no significant differences were observed between the groups after 1 year's treatment.

Treatment of non-insulin-dependent diabetes mellitus and its complications. A state of the art review

Non-insulin-dependent diabetes mellitus (NIDDM) is a major health problem which occurs predominantly in the older population; 16.8% of persons over age 65 years have NIDDM. The total health costs of NIDDM are in excess of $US20 billion annually. The primary objective in the treatment of NIDDM is to achieve normoglycaemia, without aggravating coexisting abnormalities. Common abnormalities include obesity, hypertension, retinopathy, nephropathy and neuropathies. Diet, and consequent bodyweight reduction, is the cornerstone of therapy for NIDDM. Total calorie intake should be limited, while the percentage of calories from carbohydrates should be increased and that from fats and cholesterol should be decreased. Exercise may also help to reduce bodyweight. Sulphonylurea drugs stimulate insulin secretion from beta-cells, and may be a useful adjunct to nonpharmacological therapy. Failure to respond to sulphonylurea drugs may be primary (25 to 30% of initially treated patients) or secondary (5 to 10% per year). It is not clear which is the most effective pharmacological intervention in such cases. Options include switching to or combining therapy with insulin, a biguanide, or other insulin-sparing antihyperglycaemic agents, e.g. alpha-glucosidase inhibitors, thiazolidinediones, chloroquine or hydroxychloroquine, or fibric acid derivatives such as clofibrate. Other experimental agents include the fatty acid oxidation inhibitors and dichloroacetate. Specific agents, such as antihypertensives, lipid lowering agents and sorbitol inhibitors, may be needed to prevent the complications arising from the spectrum of clinical and metabolic abnormalities which arise from insulin resistance.

Problems and pitfalls of sulphonylurea therapy in older patients

The prevalence of non-insulin-dependent diabetes mellitus (type II) increases with age, so that approximately half of all known patients in English-speaking countries are over 65 years of age. There is no reason to believe that the criteria for blood glucose control should be any less stringent for elderly patients unless they have a limited life expectancy. Sulphonylurea drugs remain an effective means of achieving blood glucose control after failure of dietary therapy alone in older patients. However, changes in normal metabolism of drugs with age and the development of other pathologies in elderly patients make it important that these drugs are prescribed with care. Severe symptomatic hypoglycaemia is the most serious adverse effect of sulphonylurea drugs and this becomes progressively more likely with increasing age, depending primarily on the substantial reduction of renal function with normal aging. Other adverse effects are much less commonly of clinical importance. To minimise the risk of hypoglycaemia, it is important that patients receive closely supervised dietary management with education about their disease for at least 3 months before sulphonylurea drugs are prescribed. In elderly patients a short-acting agent with no active metabolites should be used. As patients become older, those receiving long-acting agents can be changed to short-acting agents before problems arise. If blood glucose control appears satisfactory on treatment, then symptoms of hypoglycaemia should be sought. If control is poor, then the criteria for introduction of insulin, with appropriate education, do not differ from those in younger patients.

Inappropriate use of high-dose glyburide to treat uncontrolled type 2 diabetes mellitus

OBJECTIVE

To report a case of chronic glyburide overdose.

CASE SUMMARY

A patient with noninsulin-dependent diabetes mellitus (NIDDM) who had previously developed secondary failure while taking a maximal dosage of glipizide was switched to glyburide 5 mg/d. The patient initially experienced adequate glycemic control while taking glyburide, but subsequently experienced deterioration in glycemic control. This necessitated gradual increases in the dosage of glyburide until the maximum dosage of 20 mg/d was reached. Because the patient's diabetic control did not improve with this dosage of glyburide, she decided independently to increase the dosage further. She ingested an average daily dose of 37.7 mg of glyburide over the 18 days that preceded her clinic visit without experiencing any glyburide-related adverse effects.

DISCUSSION

Progression of NIDDM may be responsible for the development of secondary sulfonylurea failure in NIDDM patients treated with oral sulfonylurea drugs. Consequently, these patients should be treated as patients dependent on insulin.

CONCLUSIONS

NIDDM patients treated with oral sulfonylurea drugs require long-term blood glucose monitoring to detect the development of secondary sulfonylurea failure. Patients who experience secondary failure to a particular sulfonylurea drug do not appear to develop long-term blood glucose control when switched to a different oral sulfonylurea drug. These patients should be treated with insulin therapy.

Long-term effects of glipizide on insulin secretion and blood glucose control in patients with non-insulin-dependent diabetes mellitus

Of 23 patients with non-insulin-dependent diabetes mellitus (NIDDM), whose fasting blood glucose had not reached less than or equal to 6.0 mmol.l-1 after 10 weeks of dietary regulation, 15, who had had a weight reduction of -2.8 kg by dietary control, did achieve a fasting blood glucose less than or equal to 6.0 mmol.l-1 after addition of less than or equal to 20 mg glipizide daily. They had a sustained (greater than or equal to 2 years) increase in meal-induced insulin secretion (32% increase in postprandial C-peptide AUC), and a sustained reduction in postprandial hyperglycaemia (34% reduction in AUC). Ten of the patients took a mean daily dose less than 5 mg (4.8 mg) and had a sustained increase in insulin secretion rate (increased C-peptide slope). The 15 patients had no elevation of basal insulin secretion and no impairment of weight reduction. The remaining 8 subjects, who showed little or no weight reduction on dietary control, had little or no reduction in fasting blood glucose despite long-term treatment with 20 mg glipizide daily, a less sustained increase in meal-induced insulin secretion, a smaller reduction of postprandial hyperglycaemia, and an increase in body weight. On diagnosis the 8 subjects did not differ from the other 15 subjects in age, body weight, blood glucose, HbA1c, C-peptide or insulin, nor in their glucose and insulin responses to a test dose of glipizide; the main reason for the apparent drug failure appeared to be deficient compliance with dietary regulation rather than a primary inability to respond to sulphonylurea treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetic and pharmacodynamic studies of glibenclamide in non-insulin dependent diabetes mellitus

1. The pharmacokinetic and pharmacodynamic properties of oral glibenclamide have been studied in 31 hospitalised in-patients and 79 ambulant out-patients with diabetes mellitus. 2. Breakfast was found to have no significant influence on the kinetic behaviour of glibenclamide or on the effect of this drug on blood glucose utilisation. 3. The time course of glibenclamide kinetics after 20 mg dosing was adequately described by a two-compartment open model, yielding mean half-lives of 3.3 +/- 1.5 h (t1/2, lambda 1) and 9.7 +/- 1.2 (t1/2, z) for the initial and terminal elimination phases respectively. 4. No significant accumulation or change in kinetic profile occurred in patients who had normal renal and hepatic function, were treated continuously with glibenclamide, and then rechallenged after 8-12 weeks. 5. Despite inter-individual variations in drug absorption, peak plasma concentrations (Cmax) and the area under the plasma concentration-time curve (AUC(0-24] were dose-dependent over the dose range 5-20 mg. No significant dose-response behaviour was observed in respect of glucose utilisation, suggesting that there is little clinical benefit in using doses of glibenclamide above 5 mg day-1. 6. Comparison of plasma glibenclamide concentrations at different time-bands following doses of 5 and 10 mg showed a wider range in ambulant out-patients than in age-, sex-matched in-patients treated with the same dosages of drug. Mean plasma drug concentrations attained at all time bands up to 8 h after dosing were higher in out-patients than in in-patients, suggesting a tendency to 'over-compliance' by patients in anticipation of attendance at clinic.

Pharmacokinetic-pharmacodynamic relationships of oral hypoglycaemic agents. An update

Oral hypoglycaemic drugs, sulphonylureas and biguanides, occupy an important place in the treatment of Type II (non-insulin-dependent) diabetic patients who fail to respond satisfactorily to diet therapy and physical exercise. Although the precise mechanisms of action of these compounds are still poorly understood, there is sufficient agreement that sulphonylureas have both pancreatic and extrapancreatic effects, whereas biguanides have predominantly extrapancreatic actions. By using labelled compounds or measuring the circulating concentrations, the main pharmacokinetic properties of oral hypoglycaemic agents have been assessed and, in some cases, their pharmacokinetic-pharmacodynamic relationships have been evaluated. A correlation between diabetes control and plasma sulphonylurea or biguanide concentrations is generally lacking at the steady-state, with the possible exception of long-acting agents; after either oral or intravenous dosing, the reduction of plasma glucose is usually related to the increased circulating drug concentrations. The toxic effects of oral hypoglycaemic drugs are more frequent in the elderly and in the presence of conditions that may lead to drug accumulation or potentiation (increased dosage, use of long-acting compounds, hepatic and renal disease, interaction with other drugs); however, a relationship between toxic effects and drug plasma levels has been reported only for biguanides.

Sulphonylurea antidiabetic drugs. An update of their clinical pharmacology and rational therapeutic use

Apart from the amelioration of symptoms, a major aim of the treatment of non-insulin-dependent diabetes mellitus (NIDDM, type 2 diabetes) should be the prevention of cardiovascular complications. These are associated with the chronic hyperglycaemia that is characteristic of NIDDM, and the risk of complications is already increased in subjects with impaired glucose tolerance (IGT). For these reasons, and because hyperglycaemia appears to be a self-perpetuating condition, treatment should be introduced as early as possible and should be aimed at normalisation of blood glucose. To enable early detection and intervention, screening is necessary. As diet regulation alone rarely suffices to normalise blood glucose, addition of sulphonylurea drugs is indicated in many cases. If introduced in the IGT phase, sulphonylureas drugs combined with diet regulation may postpone the development of IGT to manifest NIDDM, and may reduce the increased risk of cardiovascular morbidity and mortality. Sulphonylureas stimulate insulin release, possibly via interaction with receptors in the pancreatic B cells. In addition, such treatment enhances the reduced insulin action. This might be a primary effect but is also a consequence of the increased access to insulin and the subsequent reduction of hyperglycaemia. Sulphonylureas may enhance insulin availability by reducing insulin clearance. Effects on blood lipids are probably secondary phenomena. Fast and short acting sulphonylureas may improve the impaired meal-induced acute insulin release. If combined with weight-reducing diet regulation and introduced early, such treatment can maintain (near) normal blood glucose levels and an improved insulin action for several years without increasing basal insulin secretion, without chronic hyperinsulinaemia, and without weight increase. If not combined with diet regulation, sulphonylurea therapy is likely to fail. If introduced when NIDDM is advanced, the efficacy of these drugs is limited, with secondary failures developing at a rate of 5 to 10% per year. Continuous (24-hour-a-day) exposure to drug treatment could possibly desensitise the B cell to sulphonylurea stimulation. 'Second-generation' sulphonylurea drugs have a higher potency than 'first-generation' drugs, but this need not signify a greater clinical efficacy. The effect of several of these drugs may be increased if they are ingested half an hour before meal(s). Short acting sulphonylureas may be safer than long acting ones, which seem more likely to cause long lasting and fatal hypoglycaemia, at least in elderly patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Oral hypoglycemic agents

The sulfonylureas remain the most important oral agents, although their chronic hypoglycemic actions are still unexplained and the evidence on their relative efficacy is inconclusive. Data on relative safety suggest that chlorpropamide is the most toxic sulfonylurea but glyburide causes dangerous hypoglycemia as often as chlorpropamide. For many patients, good blood glucose control will be achieved by taking tolbutamide or another sulfonylurea 30 minutes before breakfast and the main evening meal. The biguanide metformin, which is as safe as glyburide, is of use in treating overweight diabetic patients who do not have cardiovascular, hepatic, or renal dysfunction.

The relationship between the pharmacokinetics and pharmacodynamic effects of oral hypoglycaemic drugs

Oral hypoglycaemic drugs have widely differing pharmacokinetic properties. Possible pharmacodynamic benefits include greater efficacy and fewer adverse effects. In general, it has not been possible to demonstrate unequivocal differences in clinical efficacy between the sulphonylureas during long term use, although there are clear differences in potency. These differences have been emphasised to the extent that the term 'second-generation' has been used for the most potent sulphonylureas, but there is little to suggest that potency is of any therapeutic significance. Trials to study differences in efficacy have rarely been of acceptable design. They have often used fixed doses of drugs, begging the question of whether true potency ratios have been established for chronic treatment. They have rarely involved substantial numbers of patients in double-blind crossover studies with a suitable washout period. Trials which show that there is a clear relationship between drug concentrations in blood and drug effects (whether therapeutic effects or adverse effects such as severe hypoglycaemia) are generally lacking. Qualitative and semiquantitative analysis of adverse effects supports the concept that drugs with a long half-life (e.g. chlorpropamide), renally excreted active metabolites (e.g. acetohexamide) or unusual properties (e.g. glibenclamide, which accumulates progressively in islet tissue) are more likely to cause prolonged hypoglycaemia, which may be fatal. The major adverse effect of treatment with biguanides is lactic acidosis, and this probably occurs more commonly in patients treated with phenformin than those treated with metformin because of pharmacogenetic variation in phenformin metabolism. The available evidence therefore favours the use of drugs with a short elimination half-life which are extensively metabolised and which have no active metabolites.

Therapeutic equivalence of once- and thrice-daily glipizide

Two cross-over studies were carried out in 23 patients with Type 2 diabetes, to examine whether glipizide, a potent sulphonylurea with fast and complete absorption and rapid elimination (t1/2 less than 5 h), can be given once-daily without loss of therapeutic effect. In both studies, patients were randomly assigned to an initial dose of 7.5 mg once daily or 2.5 mg three-times daily, which was increased to 15 mg o.d. or 5 mg t.i.d. if the fasting plasma glucose remained over 10 mmol/l on the lower dosage. In Study 1 (n = 11), administration once a day before breakfast was compared with intake before breakfast, lunch and early dinner (5 p.m.) and in Study 2 (n = 12) the comparison was between intake once-daily before breakfast and dosing before breakfast, lunch, and at bedtime (10 p.m.). Neither the 24-hour urinary glucose excretion nor HbA1, fasting plasma glucose, insulin or C-peptide levels differed between the once and three times daily administration with the third dose given before early dinner. The nadir plasma levels of glipizide were not significantly different and were often too low to be detected. Postponing the third dose until 10 p.m. did not produce any improvement in HbA1 or in fasting plasma glucose, insulin or C-peptide. The mean nadir glipizide levels following this schedule were twice as high as those after once-daily administration. As expected, the plasma glipizide after breakfast was higher when the whole dose was taken before breakfast than when it was divided. The corresponding plasma level of insulin was higher and that of plasma glucose was lower.(ABSTRACT TRUNCATED AT 250 WORDS)

Glipizide: a second-generation sulfonylurea hypoglycemic agent. Pharmacology, pharmacokinetics and clinical use

Glipizide is a second-generation sulfonylurea in which the substitutions on the arylsulfonylurea nucleus are large, relatively nonpolar groups. This chemical change increases the intrinsic hypoglycemic activity of the molecule 100-fold on a weight basis compared to first-generation agents. In addition, the pharmacokinetic properties, spectrum and severity of side effects and metabolism of this agent are somewhat different from those of first-generation sulfonylureas. The most important component of the antidiabetic action of glipizide is its effect in potentiating insulin action. Glipizide-mediated increases in nutrient-stimulated insulin secretion may contribute to its antidiabetic action. The drug is effective in controlling the blood glucose in patients with noninsulin-dependent diabetes mellitus. It is at least as effective as and probably more effective than first-generation sulfonylureas in controlling hyperglycemia in diabetes. Glipizide is relatively free of serious side effects and is contraindicated principally in patients with significant liver or kidney disease.

Glyburide: a second-generation sulfonylurea hypoglycemic agent. History, chemistry, metabolism, pharmacokinetics, clinical use and adverse effects

Glyburide, a second-generation hypoglycemic sulfonylurea, is 200 times as potent as tolbutamide. This increase is due to greater intrinsic hypoglycemic potency of the molecule rather than to a prolonged biologic half-life. Glyburide is inactivated by the liver to 4-trans-hydroxyglyburide and 3-cis-hydroxyglyburide; 50% of these compounds is excreted in the urine and 50% in the bile. Although the serum concentration of glyburide can be measured by radioimmunoassay and high-performance liquid chromatography, the importance of its serum concentration in the reduction of hyperglycemia is not yet established. Glyburide has a therapeutic effectiveness comparable to that of the first-generation sulfonylurea chlorpropamide; however, it has a lower frequency of adverse effects. To date it has a low frequency of clinically significant interactions with other drugs. Glyburide should not be prescribed for patients with liver disease or significant renal disease. Because glyburide is a potent hypoglycemic agent, it should be prescribed in small initial doses, particularly for elderly patients with diabetes. At the present time there is no definite evidence that it modifies the increased risk of cardiovascular disease of diabetic patients. Although glyburide is a potent stimulator of pancreatic insulin secretion after short-term administration, an additional mechanism of action during long-term administration is to decrease the resistance of muscle and liver to the action of insulin. It is a useful medication for patients with type II diabetes whose hyperglycemia is not adequately reduced by dietary management and exercise. It can be used as the initial drug in these patients or as the replacement drug for those with primary or secondary failure during therapy with first-generation sulfonylureas.

Pharmacokinetics and metabolic effects of glibenclamide and glipizide in type 2 diabetics

Fifteen Type 2 diabetics were treated for 4-week periods with once daily (10 mg) glibenclamide, glipizide and placebo according to a double-blind cross-over protocol. Post-dose glipizide concentrations were three times higher than those of glibenclamide, due to the incomplete bioavailability of the latter. On the other hand, pre-dose drug levels were similar, as an expression of the slower absorption and/or elimination of glibenclamide. Both active treatments reduced postprandial blood glucose concentrations and 24-hour urinary glucose excretion to a similar degree, but fasting blood glucose concentrations were slightly lower during glibenclamide treatment. Both active treatments enhanced fasting and postprandial insulin and C-peptide concentrations, the C-peptide response being greater after glipizide than after glibenclamide. Plasma glucagon and GIP concentrations were not significantly affected. Insulin sensitivity was increased by glibenclamide but not by glipizide. Neither therapy affected insulin binding to erythrocytes. It appears that both glibenclamide and glipizide improved glucose metabolism by sustained stimulation of insulin secretion, which was most pronounced with glipizide. Only glibenclamide improved insulin sensitivity and was slightly more active than glipizide on fasting blood glucose levels. The differences may be consequences of the pharmacokinetics, but differences in pharmacodynamics cannot be excluded.

Clinical pharmacology of glipizide

The clinical pharmacology of glipizide and other sulfonylureas is briefly reviewed. Reevaluation of the University Group Diabetes Program data suggests that sulfonylureas do not increase cardiovascular mortality. Instead, a long-term study of subjects with impaired glucose tolerance indicates that sulfonylureas reduce the frequency of cardiovascular morbidity and can postpone or even prevent the development of impaired glucose tolerance to manifest diabetes. It is likely that all sulfonylureas have the same principal mechanism(s) of action but that they differ in potency and pharmacokinetics, resulting in considerable clinical differences. Thus, glipizide and glibenclamide (glyburide) are much more potent than tolbutamide and chlorpropamide. Glipizide has the most rapid absorption and onset of action, as well as the shortest half-life and effect-duration; hence the risk of long-lasting hypoglycemia is minute. Glipizide has complete bioavailability, and its blood glucose-lowering effect is improved when it is given before breakfast. Glipizide may be administered once daily without loss of therapeutic efficacy.

Influence of sulfonylureas on the secretion, disposal and effect of insulin

The influence of sulfonylurea on the secretion, disposal and effect of insulin was studied in 9 Type 2 diabetics during 3 one-month courses of treatment with a) chlorpropamide (t1/2 greater than 24 h) once daily, b) glipizide (t1/2 = 2-4 h) once daily, and c) glipizide in divided doses. Food intake by each patient was identical during each period. Blood concentrations of immunoreactive insulin (IRI) and C-peptide (radioimmunoassays), and of glucose (enzymatic assay), chlorpropamide (gas chromatography) and glipizide (high-pressure liquid chromatography) were determined before and after breakfast and lunch on the 4th day of each examination period. All comparisons were intraindividual. Despite the lunch-time dose of glipizide given during the divided dose treatment, once-daily administration of this drug led to higher drug concentrations not only after breakfast but also for the first few hours after lunch. Divided dosage, on the other hand, led to higher concentrations later. In contrast to once-daily dosage, continuous exposure to glipizide was found in most patients. Chlorpropamide gave the most continuous sulfonylurea exposure. The blood glucose levels were inversely related to the concurrent sulfonylurea concentrations; glucose levels after breakfast and lunch were lowest during once-daily glipizide, whereas the fasting level was lowest during chlorpropamide treatment. The IRI response to breakfast was 60%-70% higher during once-daily glipizide than during the other two treatments but the C-peptide responses to breakfast were almost identical. Thus, the greater after-breakfast availability of peripheral insulin appeared to be due to an effect of glipizide on the extrapancreatic disposal of the hormone.