Influence of food intake on the absorption and effect of glipizide in diabetics and in healthy subjects

Erythrocyte-mimicking subcutaneous platform with a laser-controlled treatment against diabetes

Exogenous insulin (INS) is critical for managing diabetes. However, owing to its short in vivo half-life, frequent injection of INS is un-avoidable, which is both painful and inconvenient, compromising the quality of life. Herein, we developed a laser-regulated INS release system (INS-ICG@ER hydrogel) that allowed an on-demand release of INS from the subcutaneous INS reservoir by remote laser control without the frequent injection of INS. The amino acid hydrogel functions as a hydrogel 3D scaffold material, which offers increased subcutaneous stability of drug loaded erythrocytes (ER). This INS-ICG@ER hydrogel would release INS due to the elevated content of reactive oxygen species (ROS), generated by ICG under laser irritation. Conversely, the ROS would be scavenged without the laser irradiation and stopped the release of INS from INS-ICG@ER hydrogel. Furthermore, the release of INS from INS-ICG@ER hydrogel could be regulated by laser irradiation. The INS-ICG@ER hydrogels could control the hyperglycemia within 2 h in diabetic mice and maintained their normal blood glucose level (BGL) for up to 6 days with laser irradiation 30 min prior to meals avoiding the frequent injection of free INS. This delivery system is an effective method that offers a spatiotemporally controlled release of INS to control the glucose level in vivo.

The enhancing effect of ion-pairing on the skin permeation of glipizide

The purpose of the present study was to investigate the permeation of glipizide (GP) and observe the effect of an interaction with amines as counter ions, including diethylamine, triethylamine, ethanolamine, diethanolamine, triethanolamine, N-(2-hydroxylethyl) piperidine. Permeation experiments were performed in vitro, using rat abdominal skin as a barrier. The lipophilic donor system consisting of isopropyl myristate (IPM) and ethanol (EtOH; EI system, 8:2) produced a marked enhancement of GP flux through rat skin. All the amines investigated in this study had performed an enhancing effect on GP flux, and triethylamine had the most potent enhancing effect on GP in the vehicle IPM:EtOH = 8:2(w/w). In the presence of counter ions, the solubility of GP in the donor solution (IPM:EtOH = 8:2) was increased and the log K (o/w) of GP was decreased, which may due to higher solubility of the GP in the IPM:EtOH = 8:2(w/w). (13)C NMR spectroscopy was used to identify the ion-pairing formation between GP and the respective counter ion. It was surprising that all the four enhancers examined, such as isopropyl myristate, propylene glycol, N-methyl-2-pyrrolidone, azone, and oleic acid, had no enhancing effect on the percutaneous permeation of GP. This study showed that the formation of ion-pairs between GP and counter ions is a useful method to promote the skin permeation of GP.

Comparative single-dose kinetics and effects of four sulfonylureas in healthy volunteers

The single-dose kinetics and effects of tolbutamide (500 mg), chlorpropamide (250 mg), glibenclamide (5 mg) and glipizide (5 mg) were compared in 7 healthy male volunteers by measurements of serum concentrations of the drugs and of plasma insulin and blood glucose. The drugs were administered both on an empty stomach and together with a standardized breakfast. The concentrations of tolbutamide and chlorpropamide were measured by gas chromatography, those of glipizide with high-pressure liquid chromatography, those of glibenclamide and insulin by radioimmunoassay and those of glucose by the hexokinase method. Glipizide and glibenclamide were more potent inducers of insulin release and blood glucose reduction than tolbutamide and chlorpropamide. As the concentrations of the former two drugs were in the range of nmol/l and those of the latter two in the mumol/l range, the findings support the notion that the intrinsic activity of the two second-generation sulfonylureas is at least 1 000 times greater than that of the two first-generation drugs. Glipizide seemed to be a more potent and more rapid insulin releaser than glibenclamide, but this may be secondary to biopharmaceutic differences between the two preparations. The bioavailability of glipizide was apparently greater than that of glibenclamide. Both glibenclamide (t 1/2 = 1.8 h) and glipizide (t 1/2 = 4.3 h) showed much shorter elimination half-lives than tolbutamide (7 h) and chlorpropamide (34 h). It seems probable, however, that these half-lives are not fully informative as to the duration of action of the drugs.

Effect of Nigerian meals on the pharmacokinetics of chlorpropamide in type II diabetic patients

Food-drug interactions are best evaluated on an individual drug basis, in a group of subjects in a population at risk. This is due to their complex nature, which is a function of type and size of meal, the physical and chemical form of the drug and the time lapse between food intake and drug administration. This work was aimed at investigating the effect of three different Nigerian meals, which are regularly consumed by the three major tribes in Nigeria, on the pharmacokinetics of chlorpropamide, a drug commonly used to treat Type II diabetes in this country. Meal A (maize flour meal) was composed of 81% carbohydrate, 3% protein and 11% fat; meal B (cassava flour meal) was composed of 76% carbohydrate, 3% protein and 15% fat; while meal C (browned yam flour meal) was composed of 85% carbohydrate, 2% protein and 8% fat. The effects of the three meals were investigated by administering each of the meals alone, without the medicinal drug (Treatment I); in Treatment II each meal was administered 30 min following the administration of 250 mg chlorpropamide; in Treatment III the drug was administered together with each of the standard meals. Analysis of the plasma levels of chlorpropamide was performed by high performance liquid chromatography (HPLC). Ingestion of the meal alone (Treatment I) resulted in a significant difference in postprandial plasma glucose levels. The time to maximum plasma chlorpropamide concentration was significantly increased in Treatment III (P < 0.05), while all pharmacokinetic parameters and plasma glucose levels were not significantly altered in Treatment II. Analysis of the results demonstrated a better glycaemic response with meals A and C compared with meal B.

Effects of Chinese Herbal Medicines on Intestinal Drug Absorption

Sho-saiko-to (Xiao-Chai-Hu-Tang), one of the major traditional Chinese medicines, has been frequently prescribed with other synthetic or biotechnological drugs for the treatment of various acute or chronic diseases in Japan, and thus it is important to understand the interactions between Sho-saiko-to and coadministered drugs. This paper reviews the effects of Sho-saiko-to on the pharmacokinetics and pharmacodynamics of concomitant drugs in the gastrointestinal tract. Sho-saiko-to slightly hastens the gastrointestinal absorption of the sulfonylurea compound tolbutamide. Furthermore, it is considered that the increase in the gastrointestinal absorption rate by Sho-saiko-to may potentiate the hypoglycemic effects of tolbutamide in the early period after oral administration. Sho-saiko-to can facilitate the epithelial membrane permeability of tolbutamide at an early phase across the rat jejunum in situ and Caco-2 cell monolayers. It is also suggested that Sho-saiko-to enhances the energy-dependent transport of tolbutamide and has an inhibitory effect on the passive paracellular transport of tolbutamide in Caco-2 cells. This result might be related to the accelerated in vivo absorption rate of tolbutamide by concomitant dosing with Sho-saiko-to in rats. In addition, Sho-saiko-to has inhibitory effects on the efflux pump mediated by MDR1, and it appears that the crude constituents in Glycyrrhizae radix, glycyrrhizic acid and liquiritin, contribute to MDR1 suppression.

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.

Control of postprandial hyperglycemia: optimal use of short-acting insulin secretagogues

OBJECTIVE

This study was designed to compare the efficacy of acute premeal administration of glipizide versus nateglinide in controlling postprandial hyperglycemia in subjects with non-insulin-requiring type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 20 subjects (10 female, 10 male) with non-insulin-requiring type 2 diabetes were admitted overnight to the General Clinical Research Center on four occasions. In random order, 10 mg glipizide (30 min premeal), 120 mg nateglinide (15 min premeal), 10 mg glipizide plus nateglinide (30 and 15 min premeal, respectively), or placebo pills (30 and 15 min premeal) were administered in a double-blind fashion before a standardized breakfast. Blood was drawn for analysis of glucose, insulin, and C-peptide at -0.05, 0, 0.5, 1, 2, 3, and 4 h relative to the meal.

RESULTS

The subjects were aged 56 +/- 2 years and were moderately obese (BMI 31 +/- 1 kg/m(2)), with a mean HbA(1c) of 7.4 +/- 0.4%. The peak postprandial glucose excursion above baseline was higher with placebo (6.1 +/- 0.5 mmol/l) than glipizide (4.3 +/- 0.6 mmol/l, P = 0.002), nateglinide (4.2 +/- 0.4 mmol/l, P = 0.001), or glipizide plus nateglinide (4.1 +/- 0.5 mmol/l, P = 0.001). The area under the curve for the glucose excursion above baseline was also higher with placebo (14.1 +/- 1.8 mmol/h. l) compared with glipizide (6.9 +/- 2.4 mmol/h. l, P = 0.002), nateglinide (9.7 +/- 2 mmol/h. l, P = 0.004), or glipizide plus nateglinide (5.6 +/- 2.2 mmol/h. l, P < 0.001). Peak and integrated glucose excursions did not differ significantly between glipizide and nateglinide. However, by 4 h postmeal, plasma glucose levels were significantly higher with nateglinide (9 +/- 0.9 mmol/l) compared with the premeal baseline (7.8 +/- 0.6 mmol/l, P = 0.04) and compared with the 4-h postprandial glucose level after administration of glipizide (7.6 +/- 0.6 mmol/l, P = 0.02). Integrated postprandial insulin levels were higher with glipizide (1,556 +/- 349 pmol/h. l) than nateglinide (1,364 +/- 231 pmol/h. l; P = 0.03). Early insulin secretion, as measured by insulin levels at 30 min postmeal, did not differ between glipizide and nateglinide.

CONCLUSIONS

Acute premeal administration of nateglinide or glipizide has equal efficacy in controlling postbreakfast hyperglycemia in type 2 diabetes when each drug is administered at the optimum time before the meal. Glipizide causes a more pronounced and sustained postmeal insulin secretory response compared with nateglinide. Glipizide facilitates the return to near-fasting glucose levels at 4 h postmeal, but with the possible risk of increased frequency of postmeal hypoglycemia in drug-naive patients. The clinical decision to use glipizide versus nateglinide should be based on factors other than the control of postprandial hyperglycemia in type 2 diabetes.

Comparison of the effects of three insulinotropic drugs on plasma insulin levels after a standard meal

OBJECTIVE

To compare the effects of repaglinide, glipizide, and glibenclamide on insulin secretion and postprandial glucose after a single standard 500-kcal test meal.

RESEARCH DESIGN AND METHODS

A total of 12 type 2 diabetic patients with early diabetes (mean HbA(1c) of 6.1%) and 12 matched control subjects were enrolled in this randomized, double-blind, crossover trial. Subjects received placebo, 2 mg repaglinide, 5 mg glipizide, and 5 mg glibenclamide in a random fashion during the trial. Administration of each drug was followed by a single standard 500-kcal test meal. A washout period of 7-12 days existed between the four study visits.

RESULTS

All three drugs were equally effective on the total prandial insulin secretion (area under the curve [AUC] -15 to 240 min). However, clear differences were noted in the early insulin secretion (AUC -15 to 30 min); both repaglinide and glipizide increased secretion in nondiabetic subjects by approximately 61 and 34%, respectively, compared with placebo. In the diabetic patients, the difference versus placebo was 37 and 47%, respectively. The difference between glipizide and glibenclamide reached significance in both groups of subjects, whereas repaglinide was more effective than glibenclamide only in the healthy nondiabetic subject group. All three drugs were effective in decreasing total glucose AUC in the nondiabetic and diabetic population. In the nondiabetic subjects, however, repaglinide was significantly more effective than glibenclamide. The differences disappeared in the diabetic subjects, probably as a result of increased prevalence of insulin resistance in this group.

CONCLUSIONS

Repaglinide and glipizide but not glibenclamide significantly enhanced the early insulin secretion in both nondiabetic and diabetic subjects with preserved beta-cell function after a single standard meal.

Early insulin release effectively improves glucose tolerance: studies in two rodent models of type 2 diabetes mellitus

AIM

Islet dysfunction, characterized by the loss of an acute insulin secretory response (AIR) to glucose is a well-established pathology of type 2 diabetes mellitus. Using oral insulin secreting agents with very different pharmacodynamic profiles, the present study was undertaken to test the hypothesis that, within the setting of an underlying insulin resistance, changes in the insulin response profile can differentially affect glycaemic control.

METHOD

The mildly insulin resistant high-fat fed Sprague Dawley (HF) rat and the very insulin resistant Zucker fatty (fa/fa) rat, chronically fitted with indwelling jugular cannula were subjected to an oral glucose load. Compounds were administered 5 min before the oral glucose load. Nateglinide (Nateg) was administered to elicit only an early insulin secretory response and glipizide (Glip) to elicit a later but greater insulin secretory response. Acetaminophen was used as a marker to assess for potential effects of these compounds on gastric emptying rates.

RESULTS

Nateg rapidly increased early insulin release (from -5 to 0) while the effects on total insulin release were similar to those in the controls and glucose excursions were eliminated in both diabetic models with no evidence of sustained hypoglycaemia. Conversely, Glip did not affect early insulin release but increased total insulin release (- 15 to 120 min), but only after the oral glucose load. Glip partially curbed glucose excursions in the mildly insulin resistant HF rodent and was totally ineffective in the very insulin resistant Zucker rat. The differential effects could not be attributed to effects on gastric emptying rates.

CONCLUSION

These data support the importance of early insulin release in type 2 diabetes mellitus and indicate that, independent of the level of insulin resistance, stimulating insulin release early and briefly provides for more effective and tighter glycaemic control than increasing insulin exposure to a greater magnitude later.

Differential effects of short and long duration insulinotropic agents on meal-related glucose excursions

AIM

Abnormal beta-cell function, characterized as the inability of the beta-cell to mount a rapid secretory response to glucose, is a well-established pathology of type 2 diabetes mellitus. These studies were designed to demonstrate the importance of early insulin release on the control of meal-induced glucose excursions by capitalizing on the significant pharmacodynamic differences between several oral insulin secreting agents.

METHODS

Male Sprague Dawley fitted with indwelling jugular cannulas were used to compare the pharmacodynamic profiles of nateglinide (Nateg), glipizide (Glip) and repaglinide (Repag) through frequent blood samples following the administration of these compounds via oral gavage. In similar animals which were pretrained to consume their daily food intake in two discrete 45-min meals, the effects of compound induced changes in pre-meal, meal and post-meal insulin profiles on glycaemic control were assessed through frequent blood sampling following the administration of these compounds 10 min prior to a 30-min meal.

RESULTS

There were significant pharmacodynamics differences between the three oral agents tested and the time to elicit peak insulin secretory responses increased from Nateg (4 min) to Repag (10 min) to Glip (45 min). During the meal tolerance test, glibenclamide did not increase pre-meal insulin levels and glucose excursions paralleled those in the control. Conversely, the other three agents, at doses that produced hypoglycaemic responses of similar magnitude, all increased early insulin release (Delta AUC(-15 to 3 min) = 0.5 +/- 0.01, 1.6 +/- 0.4, 3.6 +/- 0.0, 1.2 +/- 0.1 and 1.73 +/- 0.4 nmol/min, for control, Nateg at 60 and 120 mg/kg, Glip and Repag, respectively) and curbed glucose excursions during the meal at varying rates and degrees (Delta AUC(0--30 min) = 39 +/- 6, 8 +/- 7, 5 +/- 7, - 1 +/- 8 and - 3 +/- 8 mmol/min for control, Nateg at 60 and 120 mg/kg, Glip and Repag, respectively). However, unlike Nateg, the longer duration of action of Repag and Glip elicited sustained post-meal relative hypoglycaemia.

CONCLUSION

These data support the impact of early and rapid insulin release in the control of prandial and post-meal glycaemia and demonstrate that a short anticipatory burst of insulin, restricted to the beginning of a meal, provides a clear metabolic advantage and prevents post-meal hypoglycaemic episodes when compared to a greater but reactive insulin exposure that follows a meal-induced increase in glucose excursion.

Changes in the dissolution of tolbutamide by a traditional Chinese medicine, Sho-saiko-to (Xiao Chaihu Tang)

Dissolution rate is considered an important factor affecting absorption and efficacy after the oral administration of tolbutamide. Since in many cases traditional Chinese medicines, including Sho-saiko-to (TJ-9, Xiao Chaihu Tang), are taken with other drugs, it is likely that the dissolution and absorption of concomitant drugs in the gastrointestinal tract are influenced by the presence of traditional Chinese medicines. In this study, the effects of TJ-9 on the in vitro dissolution of tolbutamide were examined. We carried out the dissolution test of tolbutamide in the absence or presence of traditional Chinese medicines (Kakkon-to, TJ-1; Hachimi-jio-gan, TJ-7; Chorei-to, TJ-40; Shakuyaku-kanzo-to, TJ-68; TJ-9; Glycyrrhizae Radix, GR; glycyrrhizin, GL) by using a pH 1.2 dissolution medium. Tolbutamide was determined by HPLC assay. The moment parameters, ie., mean dissolution time (MDT), and the dissolution rate constant up to 20 min (kd) were estimated from the dissolution profiles on the basis of the first-order kinetics. Preparations containing GR, namely TJ-1, TJ-9 and TJ-68, significantly reduced the kd and increased the MDT of tolbutamide, while TJ-7 and TJ-40 had no effect on the early dissolution profile of tolbutamide. The extent of decrease in the kd in the presence of TJ-1, TJ-9 and TJ-68 was dependent on their GR contents. Similar inhibitory effects on the dissolution rate of tolbutamide were observed when GR alone was added to the test medium. In addition, GL, a major constituent of GR, induced a 50% increase in MDT and a 30% decrease in kd. The above results indicate that Chinese traditional preparations containing GR have an inhibitory effect on the in vitro dissolution of tolbutamide, which is derived from GL in the preparations.

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.

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.

The relationships between dose and concentration of tolbutamide and insulin and glucose responses in patients with non-insulin-dependent diabetes

It is uncertain how the hypoglycaemic effect of sulphonylureas varies with drug concentration in patients with non-insulin-dependent diabetes mellitus. The inter-relationship of tolbutamide dosage and concentration, and glucose and insulin concentrations were therefore examined in 54 out-patients (the observational group) and in 20 patients studied under controlled conditions (the experimental group). In the observational group, tolbutamide concentration depended significantly on the daily dose, time from dose to sampling, body weight, and age. Blood glucose and insulin concentration were related, but were independent of tolbutamide concentration. In the experimental group, peak, but not pre-dose, tolbutamide concentration, depended on dose and on body mass index. Fasting and maximum post-prandial blood glucose concentration were positively correlated with maximum tolbutamide concentration, probably because tolbutamide dosage was highest in those with the poorest response. In the subset with a fasting blood glucose concentration of less than 8 mmol.l-1, neither glucose nor insulin concentrations depended significantly on tolbutamide concentrations. Tolbutamide concentration does not directly determine hypoglycaemic response in outpatients, and therapeutic monitoring of drug concentrations would not improve the management of such patients.

The effects of ingestion time of gliclazide in relationship to meals on plasma glucose, insulin and C-peptide levels

The effect of altering the timing of gliclazide administration in relation to a meal was studied in ten type 2 (non-insulin dependent) chronically treated diabetics. Gliclazide was given 30 min before, at the start of and 30 min after breakfast or omitted altogether. Plasma gliclazide was present at greater than 2 mg/l throughout the study periods. Administration at 30 min after the meal significantly delayed the time to peak for plasma gliclazide. No significant difference was noted in plasma glucose, insulin or c-peptide patterns with any protocol. It is concluded that, in clinical practice, with chronically treated diabetics the timing of gliclazide ingestion in relation to meals is not critical.

Glipizide pharmacokinetics: effects of age, diabetes, and multiple dosing

Aging and disease may contribute to alterations in drug pharmacokinetics. The purpose of this study was to determine the effects of aging, the presence of NIDDM, and multiple dosing on the pharmacokinetics of glipizide, an oral hypoglycemic drug. Ten healthy young men (under age 25), ten healthy older men (over age 65) and 15 older diabetic men ingested a single 5 mg tablet of glipizide after an overnight fast. Blood samples for measurement of serum glipizide were obtained over the next 24 hours. The study was repeated in the diabetics after 2 weeks of daily therapy. The mean values for Tmax (range 2.0-2.5 hours), Cmax (385-465 micrograms/l), and t1/2 (4.0-4.2 hours) were not significantly different in the three populations after single doses of glipizide. Several subjects in each population had slow absorption, with peak concentrations delayed for up to 12 hours. Only one elderly diabetic subject had evidence of drug accumulation at steady state. AUC, Cl, Vss and V area were not significantly different in the three populations or at steady state, but there was a trend for AUC to be smaller and each of the other parameters to be increased in the older diabetics. The young subjects had a significantly higher fp (0.83%) than either of the two elderly groups (0.55-0.64%), but Cl int did not differ between groups. Age, diabetes, and multiple dosing appear to have little effect on the pharmacokinetics of glipizide and should have little influence on the clinical response to this drug.

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 influence of glipizide on early insulin release and glucose disposal before and after dietary regulation in diabetic patients with different degrees of hyperglycaemia

An early defect in subjects with non-insulin-dependent diabetes mellitus (NIDDM) and the preceding phase of impaired glucose tolerance (IGT) is a reduction in early insulin release and hence a prolonged elevation of postprandial blood glucose. We therefore assessed whether a rapidly acting sulphonylurea (glipizide 5 mg 0.5 h before a test meal) could correct these disturbances in 38 IGT/NIDDM subjects, whose early insulin release and postprandial blood glucose elevations remained unimproved after 10 weeks of dietary regulation. We also assessed whether the efficacy of glipizide was dependent upon the ambient blood glucose concentration, and if early systemic availability of the drug was important for the blood glucose lowering effect. A single dose of glipizide normalized early insulin release and hence reduced the postprandial blood glucose increase that was not lowered by dietary regulation. The efficacy of glipizide was dependent upon the early systemic availability of the drug, but early systemic availability and efficacy were independent of the extent of blood glucose elevation, at least within a range of 6-12 mmol.l-1 of fasting blood glucose.

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.

Non-insulin-dependent diabetes mellitus. Current status of oral hypoglycemic therapy

Proper treatment of non-insulin-dependent (type II) diabetes presents the physician with a number of choices. Diet and exercise should be tried first in many patients; if this regimen is unsuccessful, treatment with either insulin or a first- or second-generation sulfonylurea must be considered. Theoretically, second-generation agents are more advantageous than first-generation agents because they do not interact with other drugs. I do not believe that they are more efficacious, however, and they probably do not have fewer side effects if chlorpropamide (Diabinese) is eliminated from consideration. Future well-designed crossover studies may help to clarify this issue. Combined insulin and sulfonylurea therapy can be tried in obese patients resistant to large doses of insulin, although results are not dramatic. In all patients the goal is to reach acceptable fasting glucose levels and near-normal glycosylated hemoglobin values.

Clinical pharmacology of sulfonylureas

Sulfonylureas seem to have similar mechanisms of action, including an acceleration and increase of insulin secretion, an increase of the systemic availability of insulin, and probably indirectly, an increase of insulin action. Sulfonylureas may postpone the development of impaired glucose tolerance (IGT) to manifest non-insulin-dependent diabetes mellitus (NIDDM), and all NIDDM subjects should benefit from sulfonylurea treatment except those in whom insulin secretion has been attenuated. The most effective use is the combination of diet restriction and sulfonylurea introduced in NIDDM subjects soon after transition from IGT to NIDDM. A simple screening procedure has been devised to find the subjects at this early stage. Newer sulfonylureas, such as glipizide and glyburide, are more potent than the older ones, such as tolbutamide and chlorpropamide. During chronic treatment, glipizide and glyburide seem to be equally effective in reducing blood glucose levels, and they do so without causing a chronic elevation of insulin secretion, signifying that they do not increase the risk of pancreatic B cell exhaustion. Glipizide has rapid and complete absorption, as well as a rapid distribution and elimination. This may explain why it is less liable than other sulfonylureas to provoke long-lasting hypoglycemia, which is the major danger when using sulfonylureas. Despite its rapid elimination, 7.5 to 15 mg glipizide can be administered once daily without loss of therapeutic efficacy. This may be due in part to enterohepatic recirculation of the drug in response to meals. The therapeutic efficacy is increased if glipizide is received half an hour before breakfast.

Serum gliclazide concentration in diabetic patients. Relationship between gliclazide dose and serum concentration

Serum levels of gliclazide were determined by radioimmunoassay in seven healthy controls and in 18 diabetic in-patients receiving single oral dosing and consecutive dosing over 5 days. Following a single oral dose of 40 mg in the seven controls and eight diabetic patients, and 120 mg in ten diabetic patients, the serum levels of gliclazide peaked on average at 2 h, followed by a slow decline, the t1/2 being 16.5 h in the volunteers, 12.3 h in the diabetic patients receiving 40 mg, and 10.5 h in those receiving 120 mg. During consecutive administration, the serum levels both at fasting and at the peak reached a plateau in 2 days and no further accumulations were observed. The steady-state peak levels of gliclazide in the diabetic patients revealed a strongly positive correlation with the dose per m2 body surface area (r = 0.78, P less than 0.001), and their steady-state fasting levels correlated positively but weakly with the dose per m2 body surface area (r = 0.48, P less than 0.05). Thus, measuring either the fasting or the peak concentration of gliclazide will be useful for monitoring drug concentration in the serum. Pharmacokinetics of gliclazide will contribute to the elucidation of the relationship of serum level and clinical effectiveness in diabetic subjects.

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)

Review of glyburide after one year on the market

After one year on the American market, glyburide, a second-generation sulfonylurea, seems well accepted by physicians. If the hyperglycemia of patients with type II diabetes mellitus is not corrected by diet and exercise, glyburide can be used as adjunctive therapy. The drug is comparable in efficacy to the first-generation sulfonylurea chlorpropamide, but it has fewer reported side effects. Additionally, glyburide does not appear to interact with other medications and is well absorbed from the gastrointestinal tract. Although the drug had been reported to produce hypoglycemia, increased clinical experience--along with use of judicious dosages in appropriate patients--has decreased the incidence of hypoglycemia. Although still in the investigational stage, combination insulin/glyburide therapy may also benefit subgroups of type II diabetic patients. Glyburide is a useful and rational addition to therapy in properly selected patients with type II diabetes mellitus.

The second generation sulfonylureas: glipizide and glyburide

Glyburide and glipizide are approved by the FDA for treatment of symptomatic and asymp tomatic NIDDM patients in whom hyperglycemia cannot be satisfactorily controlled by diet and exercise. Pharmacology studies suggest that glyburide and glipizide sensitize the beta cells of the pancreas to release insulin only in the presence of elevated serum glucose levels. Long-term efficacy appears to depend on extrapancreatic effects, suppressing hepatic glucose production, and improved postreceptor insulin activity.

Effect of food and tablet age on relative bioavailability and pharmacodynamics of two tolbutamide products

Relative bioavailability and pharmacodynamics of tolbutamide from two different commercially available tablet products have been evaluated in healthy subjects in a single-dose crossover study. "Fresh" tablets and tablets aged by exposure to 98% relative humidity for 3 d at ambient temperature were studied. Aging was found to differentially affect both the rate and extent of absorption for the two products. Differences were reflected by log AUC (generic product AUC 10% lower than the product of the innovator, p = 0.047), peak concentration (generic product 27% lower than the product of the innovator, p = 0.0001), mean absorption time (generic product 119% longer than the product of the innovator, p = 0.0008), and mean residence time (generic product 17% longer than the product of the innovator, p = 0.011). Aged product from the innovator produced statistically significantly higher serum tolbutamide concentrations for the first 8 h postdose and a greater glucose depression than aged generic product. Administration of unaged tablets with food produced differences in the rate of absorption, manifested in time-to-peak (generic product 69% later than the product of the innovator, p = 0.006), peak concentration (generic product 18% lower than the product of the innovator, p = 0.001), and mean absorption time (generic product 104% greater than the product of the innovator, p = 0.007), which resulted in statistically significantly higher tolbutamide concentrations for the product of the innovator than for the generic product for the first 3 h postdose.(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.

Effect of guar gum on glipizide absorption in man

The effect of 4.75 g guar gum, a fibre preparation, on the absorption of 2.5 mg glipizide has been studied in 10 healthy volunteers given a standard breakfast. Three different experimental protocols were used: glipizide without guar gum (Treatment 1), glipizide with guar gum (Treatment 2) and guar gum 30 min after the drug together with breakfast (Treatment 3). The serum glipizide at 30 minutes was higher during Treatment 2 than Treatment 3 (p less than 0.01), but neither differed from the control treatment. The AUCs for glipizide were calculated up to 8 hours. They did not differ significantly between the treatment, although there was a non-significant trend to lower values during Treatment 3. Serum insulin and blood glucose levels were determined up to 3 h. Corresponding to differences in the glipizide concentration, serum insulin was highest and blood glucose lowest at 30 minutes during Treatment 2. According to this single dose study, guar gum does not have any substantial deleterious effect on the absorption of glipizide. The lack of effect may be due to the complete gastrointestinal absorption of glipizide.

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.

Interactions affecting drug absorption

The influence of drug-drug and drug-food interactions affecting the absorption of orally administered medication is reviewed. Drug-drug interactions can be classified in terms of indirect effects by one drug on gastrointestinal tract physiology influencing the absorption of other drugs, or direct interactions involving altered pH, adsorption, absorption, or chelation. Most, but not all, drug-drug interactions result in reduced or delayed systemic drug availability. Drug-food interactions may result in reduced, delayed, or increased systemic drug availability. The absorption of only a small number of drugs is unaffected by concomitant food intake. The degree of interaction and whether it positively or negatively affects drug absorption depends on a number of factors including the physical and chemical nature of the drug, the formulation, the type of meal, and the time interval between eating and dosing. Mechanisms of drug-food interactions are not well characterised. They clearly involve both direct and indirect factors in a similar fashion to drug-drug interactions, but indirect factors probably predominate. Reduced or delayed drug absorption is generally attributed, at least in part, to delayed stomach-emptying due to food. Increased absorption may also result from delayed stomach-emptying facilitating greater drug dissolution before it passes from the stomach into the small intestine. Increased bioavailability of some drugs, e.g. propranolol, metoprolol and labetalol, may be related to reduced presystemic clearance. The potential clinical implications of drug-drug and drug-food interactions must be taken into account with oral medications in order to minimise variations in systemic drug availability and hence in clinical efficacy.

Glipizide increases plasma insulin but not C-peptide level after a standardized breakfast in type 2 diabetic patients

Peripheral blood glucose, plasma insulin and C-peptide levels were investigated after giving a standardized breakfast (500 kcal, 60 g carbohydrates) to 10 nonobese Type 2 diabetic patients previously treated by diet alone. Each patient received at random, at 1 week intervals, either 5 mg glipizide (meal + glipizide) or a placebo (meal alone) 30 min before breakfast. Basal values of blood glucose, plasma insulin and C-peptide were similar on both occasions. After meal + glipizide, the blood glucose increase was sharply limited whereas the rise in plasma insulin was steeper and reached twice as high a level. In contrast, the rise in plasma C-peptide was similar in both conditions. Consequently, the areas under the curves (0-300 min) showed a marked reduction in blood glucose after meal + glipizide (2289 +/- 149 versus 3101 +/- 169 mmol X min/1; 2p less than 0.001), associated with a significant increase in plasma insulin (14219 +/- 3261 versus 7591 +/- 1173 microU X min/ml; 2p less than 0.025) but no significant change in plasma C-peptide (342 +/- 45 versus 326 +/- 34 pmol X min/ml; N.S.). The insulin/C-peptide molar ratio was thus significantly increased after meal + glipizide (0.41 +/- 0.06 versus 0.23 +/- 0.04 at the 60th min; 2p less than 0.02). The dissociation between the responses of insulin and C-peptide suggests that a single dose of 5 mg glipizide in Type 2 diabetic subjects may enhance availability of peripheral insulin by extrapancreatic mechanism(s). This phenomenon may result in a higher circulating level of the hormone and therefore represent a further mode of action of sulphonylureas.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

The effect of food on the bioavailability and pharmacodynamics of tolbutamide in diabetic patients

The effect of food on the rate and extent of absorption of tolbutamide in diabetic patients was studied by varying the time of drug administration in relation to the ingestion of a standard meal. Serum levels of tolbutamide, insulin and glucose and related bioavailability parameters were compared following the administration of a single dose of tolbutamide 0.5 g to diabetic patients 30 min prior to and immediately before a standardized meal. A placebo dosage form was also administered to determine baseline glucose and insulin response to the meal. The 700 calorie standard meal was composed of 41% carbohydrate, 18% protein, and 41% fat. Administration of the drug with the meal resulted in a 6% (statistically significant) decrease in the extent of absorption, as determined by measurement of the area under the tolbutamide serum level-time curve from zero to infinity. Serum levels of tolbutamide were also significantly higher 0.5 h after drug administration when the drug was taken with the meal. Except for these two minor effects, no other differences between the drug treatments were observed in any other parameters of tolbutamide absorption or in the postprandial glucose and insulin serum levels. Therefore, the small differences found were judged to be clinically meaningless. These findings demonstrate that administration of tolbutamide 0.5 g tablets 30 min prior to or with a standard meal results in equivalent therapeutic actions.