Oral hypoglycaemic agents. An update

Time-based investigation of urinary metabolic markers for Type 2 diabetes: Metabolomics approach for diabetes management

Diabetes is considered one of the most important health emergencies worldwide and Egypt has 8.2 million diabetic patients according to the International Diabetes Federation report in 2017. The objective of this study was to monitor the time-course variation in the metabolic profile of diabetic rats to detect urinary metabolic biomarkers using the metabolomics approach. Type 2 diabetes was induced in male Wistar albino rats using a single intraperitoneal injection of 40 mg/kg of streptozotocin following oral administration of 10% fructose in drinking water for 3 weeks. Then, urine was collected for 24 h from rats at three time points (0, 2, and 4 weeks after confirmation of diabetes), and were analyzed by nuclear magnetic resonance (H¹ -NMR), followed by multivariate data analysis. The results from H¹ -NMR pointed out that d-glucose, taurine, l-carnitine, l-fucose, 1,5-anhydrosorbitol, and d-galactose levels showed consistent significant variation (p < 0.05) between the positive (diabetic) and negative (normal) controls during the whole experimental period. Also, with the disease progression, myoinositol, and l-phenylalanine levels were significantly altered (p < 0.05) after 2 weeks and this alteration was maintained till the end of the 4-week experimental period in the positive control group. From the results of the present study, it could be concluded that we cannot depend only on glucose levels for prognostic purposes since there are other metabolic disturbances in diabetes which need to be tracked for better disease prognosis.

The beneficial effects of metformin on cancer prevention and therapy: a comprehensive review of recent advances

Metformin is a widely used drug in today’s prescriptions by physicians due to its specific effects in treating and curing type II diabetes. Diabetes is a common disease that may occur throughout human life, and can increase the likelihood of the occurrence of various types of cancer, such as colon, rectum, pancreas and liver cancers, compared to non-diabetic patients. Metformin inhibits mTOR activity by activating ATM (ataxia telangiectasia mutated) and LKB1 (liver kinase B1) and then adenosine monophosphate-activated kinase (AMPK), and thus prevents protein synthesis and cell growth. Metformin can activate p53 by activating AMPK and thereby ultimately stop the cell cycle. Given the potential of metformin in the treatment of cancer, it can be used in radiotherapy, chemotherapy and to improve the response to treatment in androgen derivatives (ADT), and also, according to available evidence, metformin can also be used to prevent various types of cancers. Generally, metformin can: 1) reduce the incidence of cancers, 2) reduce the mortality from cancers, 3) increase the response to treatment in cancer cells when using radiotherapy and chemotherapy, 4) optimize tumor movement and reduce the malignancy, 5) reduce the likelihood of relapse, and 6) reduce the damaging effects of ADT. Therefore, this drug can be used as a complementary therapeutic agent for cancer treatment and prevention. In this review, we have summarized the data from various experimental and clinical studies and highlight the possible potential effects of metformin on cancer therapeutic responses.

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Renal Denervation: A Potential Novel Treatment for Type 2 Diabetes Mellitus?

Type 2 diabetes mellitus (T2DM) is a group of metabolic diseases of multiple etiologies. Although great progress has been made, researchers are still working on the pathogenesis of T2DM and how to best use the treatments available. Aside from several novel pharmacological approaches, catheter-based sympathetic renal denervation (RDN) has gained a significant role in resistant hypertension, as well as improvements in glycemic control in T2DM.In this article, we will summarize herein the role sympathetic activation plays in the progression of T2DM and review the recent clinical RDN experience in glucose metabolism.We performed systematic review in online databases, including PubMed, EmBase, and Web of Science, from inception until 2015.Studies were included if a statistical relationship was investigated between RDN and T2DM.The quality of each included study was assessed by Newcastle-Ottawa scale score. To synthesize these studies, a random-effects model or a fixed-effects model was applied as appropriate. Then, we calculated heterogeneity, performed sensitivity analysis, tested publication bias, and did meta-regression analysis. Finally, we identified 4 eligible articles.In most studies, RDN achieved via novel catheter-based approach using radiofrequency energy has gained a significant role in resistant hypertension, as well as improvements in glycemic control in T2DM. But the DREAMS-Study showed that RDN did not change median insulin sensitivity nor systemic sympathetic activity.Firstly, the current published studies lacked a proper control group, along with the sample capacity was small. Also, data obtained in the subgroups of diabetic patients were not separately analyzed and the follow-up period was very short. In addition, a reduction in blood pressure accounts for the improvements in glucose metabolism and insulin resistance cannot be excluded.If the favorable result of better glucose metabolism is confirmed in large-scale, randomized studies, RDN may emerge as a novel therapeutic option for patients with T2DM.

Pathophysiology and treatment of type 2 diabetes: perspectives on the past, present, and future

Glucose metabolism is normally regulated by a feedback loop including islet β cells and insulin-sensitive tissues, in which tissue sensitivity to insulin affects magnitude of β-cell response. If insulin resistance is present, β cells maintain normal glucose tolerance by increasing insulin output. Only when β cells cannot release sufficient insulin in the presence of insulin resistance do glucose concentrations rise. Although β-cell dysfunction has a clear genetic component, environmental changes play an essential part. Modern research approaches have helped to establish the important role that hexoses, aminoacids, and fatty acids have in insulin resistance and β-cell dysfunction, and the potential role of changes in the microbiome. Several new approaches for treatment have been developed, but more effective therapies to slow progressive loss of β-cell function are needed. Recent findings from clinical trials provide important information about methods to prevent and treat type 2 diabetes and some of the adverse effects of these interventions. However, additional long-term studies of drugs and bariatric surgery are needed to identify new ways to prevent and treat type 2 diabetes and thereby reduce the harmful effects of this disease.

Enhancement of glucose uptake in 3T3-L1 adipocytes by Toona sinensis leaf extract

The effects of substances extracted from Toona sinensis leaves, using 50% alcohol/water, on cellular [3H]-2-deoxyglucose uptake in differentiated cultured 3T3-L1 adipocytes were investigated. Following treatment of cells with 0.001, 0.01, or 0.1 mg/mL extracts for 60 minutes, [3H]-2-deoxyglucose uptake increased from a basal value of 0.23 nmol/min/mg protein to 0.30, 0.33, and 0.38 nmol/min/mg protein, respectively. In insulin-stimulated cells, cellular [3H]-2-deoxyglucose uptake was enhanced by Toona sinensis leaf extract from a basal value of 0.35 nmol/min/mg protein to 0.41, 0.46, and 0.52 nmol/min/mg protein, respectively. Cellular glucose uptake was also enhanced by Toona sinensis leaf extract after incubation of cells with 20 mM glucose for 48 hours. Cellular glucose uptake with a combination of Toona sinensis leaf extract and insulin was significantly inhibited by pretreatment of cells with the protein synthesis inhibitor cycloheximide and the protein kinase C inhibitor calphostin C in normal-, medium- and high-glucose media. However, the glucose uptake-enhancing effect of Toona sinensis leaf extract was not diminished by cycloheximide and calphostin C in the absence of insulin. These results indicate that enhancement of cellular glucose uptake by Toona sinensis leaf extract in basal and insulin-stimulated 3T3-L1 adipocytes may be mediated by distinct mechanisms.

Drug Poisoning and Overdose for the Health Professional: Review of Select Over-the-Counter (OTC) and Prescription Medications

Exposure to over-the-counter and prescription medications can pose significant therapeutic and health hazards to patients, and present health care professionals with scenarios that require proper assessment and treatment. Knowing when an exposure to or overdose of a drug requires emergency medical attention is equally as important as to knowing when such assistance is not necessary—that simple treatment measures performed at home will suffice. This current discussion is intended to highlight select principles and clinical information pertaining to common drug exposures and overdoses, but not replace the full spectrum of information that would be available to health care professionals (and the lay public) by contacting their nearest poison control center. Many of the basic principles and concerns that are encountered with exposures to chemicals (i.e., route of exposure, patient medical history, quantity of the substance involved, elapsed time since the initial exposure, etc.) apply equally well to drug exposures. Likewise, evaluating each of these variables will determine which type of treatment approaches are, and are not, considered in situations of drug (or chemical) exposure and overdose.

Rates of hypoglycemia in users of sulfonylureas

OBJECTIVE

To identify the demographic and clinical characteristics of sulfonylurea users. To assess the risk of hypoglycemia in patients treated with sulfonylureas in clinical practice, and to characterize the risk in relation to the different drugs used.

RESEARCH DESIGN AND METHODS

A cohort of 33,243 sulfonylurea users chosen from 719 clinical practices in the United Kingdom were identified through the VAMP-Research database. Information on demographic characteristics, medical diagnoses and use of medical services was obtained through the computerized records. For a stratified sample of 500 patients, general practioners completed a structured questionnaire on the duration, treatment, and complications of diabetes mellitus, obesity, alcohol use, and smoking history. Patients with a diagnosis of hypoglycemia, as recorded in the database within a time-window of a sulfonylurea prescription, were identified. Incidence rates per person-year of sulfonylurea therapy were estimated.

RESULTS

Other than a longer duration of diabetes in users of chlorpropamide, no differences were observed among users of different sulfonylurea agents with respect to diabetic complications, adequacy of diabetic control, obesity, smoking, and excessive alcohol consumption. A diagnosis of hypoglycemia during sulfonylurea therapy was recorded in 605 people over 34,052 person-years of sulfonylurea therapy, which converted into an annual risk of 1.8%. The risk in glibenclamide users was higher than in users of other types of sulfonylureas uses. Duration of therapy, concomitant use of insulin, sulfonylurea-potentiating or antagonizing and concomitant use of beta-blockers were predictive of the risk of developing hypoglycemia.

DISCUSSION

Drug use patterns showed comparability among users of different sulfonylurea agents. Our findings suggest that the rate of diagnosis of hypoglycemia made by physicians is higher for glibenclamide than for other sulfonylureas. An epidemiological study with objectively diagnosed hypoglycemia should be undertaken to confirm these results.

Oral antidiabetic drug use in the elderly

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

NIDDM in the cat: treatment with the oral hypoglycemic medication, glipizide

The oral hypoglycemic medication, glipizide, provides a viable therapeutic alternative to conventional insulin therapy with a positive therapeutic response in approximately 50% of diabetic cats with non-insulin-dependent disease. Response to glipizide therapy or lack thereof usually is evident within the first 4 to 6 weeks of treatment. Adverse side effects occurred in less than 10% of patients. The existence of residual beta cell function is necessary for response to glipizide therapy. Predictors of response to glipizide therapy were not found. Identification and correction or control of existing insulin antagonistic disease processes, as well as, discontinuation of diabetogenic medications that may be contributing to insulin resistance is also important.

Effect of the hypoglycaemic drug (-)-AZ-DF-265 on ATP-sensitive potassium channels in rat pancreatic beta-cells

1. It has previously been shown that the hypoglycaemic drug (-)-AZ-DF-265 stimulates insulin release from mouse islets; in the presence of 3 mM glucose it also inhibits 86Rb-efflux from 86Rb-loaded islets. Based on these data we tested the hypothesis that (-)-AZ-DF-265 inhibits ATP-sensitive potassium channels. 2. We voltage-clamped the plasma membrane of single rat pancreatic beta-cells in the whole-cell configuration and measured the current flowing through ATP-sensitive potassium channels. (-)-AZ-DF-265 was applied to the outside of the cell; it inhibited the current half-maximally at a concentration of 1.2 +/- 0.2 nM with a Hill coefficient of 0.7 +/- 0.1. The inhibition was reversible on washing. 3. In intact RINm5F cells, the sulphonylurea [3H]-glibenclamide bound with an affinity of 0.24 +/- 0.01 nM and a Hill coefficient of 2.1 +/- 0.4. Treatment with (-)-AZ-DF-265 led to the displacement of [3H]-glibenclamide; this effect was half-maximal at 8.6 +/- 1.7 nM and displayed a Hill coefficient of 0.53 +/- 0.01. Meglitinide and tolbutamide, which represent, respectively, the benzamido and sulphonylurea moieties of glibenclamide, showed Hill coefficients of 0.8 +/- 0.1 and 0.9 +/- 0.1, respectively. 4. At pH 7.4 and with phosphate/borate buffer, (-)-AZ-DF-265 had an apparent octanol/water partition coefficient of about 53, which is intermediate between the partition coefficients of glibenclamide and glipizide. Nevertheless, (-)-AZ-DF-265 bound only to a minor degree to glass and plastic.5. In conclusion, (-)-AZ-DF-265 inhibits ATP-sensitive potassium channels and displaces [3H]-glibenclamide from the sulphonylurea receptor.

Effect of glipizide on serum insulin and glucose concentrations in healthy cats

With the recent identification of non-insulin-dependent diabetes mellitus (NIDDM) in cats, new possibilities arise for the use of oral hypoglycaemic agents in the treatment of feline NIDDM, similar to their use in humans. To identify the future applicability of the oral hypoglycaemic agent, glipizide, in the treatment of feline NIDDM, its effects on serum insulin and glucose concentrations in healthy cats was examined. In addition, adverse effects seen clinically or on bloodwork following short-term use of the drug were looked for. Serum insulin and glucose concentrations were evaluated after the oral administration of 2.5, 5.0 and 10.0 mg glipizide and placebo in 10 healthy cats. For each drug trial, blood was obtained five minutes before, immediately before, and 7.5, 15, 30, 45, 60, 90 and 120 minutes after glipizide or placebo administration. Mean serum insulin concentration increased after glipizide administration, with peak mean serum insulin concentration occurring 15 minutes after administration and declining to baseline by 60 minutes. There was no significant difference in peak mean serum insulin concentration, mean serum insulin concentration at 60 minutes after glipizide administration, or mean total insulin secretion between the three glipizide dosages. Mean serum glucose concentration decreased within 15 minutes of glipizide administration, with the glucose nadir occurring 60 minutes after glipizide administration. Placebo trials showed no significant change in mean serum insulin or glucose concentrations from baseline concentrations.

The influence of hypoglycaemic agents on the growth and metabolism of human endothelial cells

Using human umbilical vein endothelial cells, and human microvascular endothelial cells from omental and subcutaneous fat obtained at laparotomy, we studied the effects of sulphonylureas and the biguanide metformin on endothelial cell proliferation, prostacyclin production, ecto-5'-nucleotidase activity, and von Willebrand factor release. Each drug produced a concentration-dependent proliferation of umbilical vein but not of microvascular endothelial cells. The stimulation of umbilical vein endothelial cell proliferation by sulphonylureas, but not by metformin, was serum- and insulin-dependent. Sulphonylureas and metformin had no effect on the proliferation of human dermal fibroblasts, smooth muscle cells derived from the umbilical artery, or 3T3 cells, until concentrations greater than 100 fold those found in vivo were reached, when there was inhibition of proliferation. These agents had no effect on prostacyclin or von Willebrand factor production, or on ecto-5'-nucleotidase activity, until high concentrations were used, at levels which also inhibited proliferation. The results suggest that the sulphonylureas and metformin, may, at concentrations found in vivo, induce changes in the turnover of endothelial cells from large vessels, but not of microvascular endothelial cells.

Lack of effect of tenoxicam on dynamic responses to concurrent oral doses of glucose and glibenclamide

1. In a single-blind, placebo controlled study the influence of tenoxicam on responses of glucose, insulin and C-peptide to oral doses of glucose and glibenclamide was examined in 16 healthy male volunteers. 2. The subjects received once daily doses of 2.5 mg glibenclamide for 12 days. From day 5 through 12 eight subjects received concomitantly 20 mg tenoxicam once daily and the remaining eight subjects received placebo. 3. On days 1, 4, 5 and 12 glibenclamide was taken with 75 g glucose and blood glucose, serum insulin and C-peptide were measured over 5 h. Plasma levels of glibenclamide and tenoxicam (where appropriate) were followed over 10 h. 4. Characteristic parameters of blood glucose and insulin and C-peptide responses did not change significantly with time (day) and there was no difference between both treatment groups. 5. Baseline insulin increased from 11.7 mu l-1 on day 1 to 15.6 mu l-1 on day 4 (P = 0.009), likewise baseline C-peptide increased from 478 pmol l-1 to 530 pmol l-1 (P = 0.05), but there was no further change in the subsequent treatment period. 6. The AUC of the glibenclamide plasma concentration-time curve did not show changes with time or differences between treatment groups. The mean (s.d.) oral clearance of tenoxicam was 2.5 (1.5) ml min-1 and appeared slightly higher than in previous studies. 7. It was concluded that tenoxicam did not affect overall glycoregulation in healthy subjects under glibenclamide steady state conditions.

The hypoglycaemic and insulinotropic activity of Tinospora crispa: studies with human and rat islets and HIT-T15 B cells

In Malaysia, Tinospora crispa extract is taken orally by Type 2 (non-insulin-dependent) diabetic patients to treat hyperglycaemia. We have evaluated the claimed hypoglycaemic property by adding aqueous extract to the drinking water of normal and alloxan-diabetic rats. After one week, fasting blood glucose levels were significantly (p less than 0.01) lower and serum insulin levels were significantly (p less than 0.01) higher in treated diabetic animals (10.4 +/- 1.0 mmol/l and 12.8 +/- 1.1 muU/ml respectively) compared to untreated diabetic controls (17.4 +/- 1.7 mmol/l and 8.0 +/- 0.7 muU/ml respectively). The insulinotropic action of T. crispa was further investigated in vitro using isolated human or rat islets of Langerhans and HIT-T15 cells. In static incubations with rat islets and HIT-T15 B cells, the extract induced a dosage dependent stimulation and potentiation of basal and glucose-stimulated insulin secretion respectively. This insulinotropic effect was also evident in perifused human and rat islets and HIT-T5 B-cells. The observations that (i) in all three models insulin secretory rates rapidly returned to basal levels on removal of the extract and (ii) in rat islets, a second challenge with T. crispa induced an additional, stimulated response, are all consistent with physiological release of insulin by B cells. Moreover, the rate of HIT-T15 glucose utilisation was not affected by incubation with T. crispa, suggesting that the cells were viable throughout. These are the first studies to provide biochemical evidence which substantiates the traditional claims for an oral hypoglycaemic effect of Tinospora crispa, and which also show that the hypoglycaemic effect is associated with increased insulin secretion.

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.

The effect of glipizide on extraction of insulin by the human cirrhotic and noncirrhotic liver

The effect of glipizide on hepatic uptake of insulin was studied in five patients with liver cirrhosis and five patients with varying diseases in the biliary system and pancreas. All patients had portal catheters for diagnostic purposes. The hepatic uptake of insulin was estimated from the clearance rate for insulin obtained after a constant rate infusion into a peripheral vein and the portal vein. Each patient was examined on two consecutive mornings, the second investigation carried out one hour after oral glipizide administration. The fractional hepatic uptake was significantly lower in cirrhotic patients (17% +/- 6%) than in the other patients (52% +/- 7%; P less than .01). After glipizide, an increase in the estimated uptake of insulin occurred in cirrhotic patients (from 17% +/- 6% to 39% +/- 6%; P less than .01), whereas an insignificant decrease was observed in the other patients (from 52% +/- 7% to 43% +/- 11%).

A comparison of cellular actions between gliclazide and a hypoglycaemic peptide fragment of human growth hormone (hGH 6-13)

The mechanisms of hypoglycaemic action of a 'second-generation' sulphonylurea, gliclazide, and a synthetic human growth hormone fragment, hGH 6-13 (Leu-Ser-Arg-Leu-Phe-Asp-Asn-Ala), were compared at the cellular level in rats. Both compounds were shown to be hypoglycaemic in vivo although their molecular structures were totally different. Gliclazide was markedly insulinotropic, as are all hypoglycaemic sulphonylureas, whereas hGH 6-13 had no visible effect on basal levels of plasma insulin. However, in vitro studies with isolated pancreatic islets revealed that hGH 6-13 significantly augmented insulin secretion in the presence of exogenous glucose. One other major difference was that gliclazide had no direct effect on insulin receptor function while the synthetic hGH 6-13 increased the binding of insulin to specific receptors on isolated cells. Results suggested that the human growth hormone fragment hGH 6-13 could be a potential anti-diabetes drug with the ability to potentiate circulating insulin action and to achieve blood glucose normalisation.

Effects of sulfonylureas on the synthesis and secretion of plasminogen activator from bovine aortic endothelial cells

The effects of sulfonylureas on the production of plasminogen activator (PA) and antiactivator (PAI) were investigated using bovine aortic endothelial cells. All compounds studied stimulated PA release (1.3- to 5.2-fold), with glipizide being the most potent, followed by tolazamide, chlorpropamide, and tolbutamide, in that order, while glyburide was the least effective. Both tissue-type and urokinase-type PA production was enhanced. Studies using metabolic inhibitors indicated that both RNA and protein syntheses are required for the sulfonylurea-mediated stimulation of PA release. In addition to continuous release of the two PAs, there was also a continuous release of a single PAI, which did not show an increase after the sulfonylureas. These results suggest that, in addition to their beneficial effects in the treatment of diabetes mellitus, some sulfonylurea compounds may also have significant thrombolytic effects. These results also suggest that pharmacological enhancement of PA production by vascular endothelial cells may be a promising antithrombotic mechanism.

Protocols for the treatment of essential hypertension and type II diabetes mellitus by pharmacists in ambulatory care clinics

During the last several years, the pharmacist has acted as a primary-care provider for patients with selected chronic illnesses at an urban county health department. The pharmacist's responsibilities include examining patients, ordering laboratory tests and X-rays, and adjusting or prescribing medication. In order to comply with health department regulations requiring the use of protocols by non-physician practitioners, and to better define the pharmacist's role, pharmacy protocols for the treatment of essential hypertension and type II diabetes mellitus have been developed. The protocols provide specific guidelines for the pharmacist involved in primary patient care. In addition, they describe a procedure for the selection and referral of patients. These protocols can serve as a sound foundation by which other pharmacists involved with primary patient care treat essential hypertension and type II diabetes mellitus. They can easily be modified to suit a pharmacist's particular needs and situation.

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.

Genetic variation in the human hepatic cytochrome P-450 system

Studies in rodents indicate that the cytochrome P-450 system consists of a superfamily of heme proteins, produced by clusters of structural genes on different chromosomes. Equivalent P-450s of different species show more homologies than members of different P-450 families within a species. The Ah receptor serves the induction of members of one of the cytochrome families. The human structural gene for the methylcholanthrene-inducible P1-450 is located on Chromosome 15. This gene has been completely sequenced. The human Ah receptor is also measurable. New methods to measure inducibility in man involve new lymphocyte bioassays and mRNA determinations, while in vivo biotransformation studies of caffeine allow estimates of the state of induction. Structural genes for phenobarbital-inducible cytochromes have been localized to Chromosome 19. The deficiency of biotransformation of debrisoquine and sparteine continues to be explored intensely. Linkage studies indicate the gene for the variable cytochrome P-450 to be located on Chromosome 22. The deficiency is more likely due to structural variation than absence of the cytochrome. Inhibiting drugs can mimic the genetic defect. Many pharmacological and toxicological consequences of the deficiency have been defined. The main characteristics of the genetic deficiencies affecting the metabolisms of mephenytoin, phenytoin, tolbutamide, nifedipine and of methyl cysteine were outlined briefly.

Pharmacokinetics of glyburide

The pharmacokinetics of glyburide can be described by a two-compartment open model. Terminal-phase descriptions are formulation-dependent and are complicated by apparent food-associated mobilization of drug from the stomach. Some researchers indicate a possible third (or deep) compartment, but this appears to be an artifact of a nonspecific drug assay. Although no accumulation has been observed in short-term studies, further investigation of the possibility of drug accumulation with long-term therapy is needed. Distribution of glyburide is affected by high affinity for serum albumin (99 percent bound), and elimination of the drug appears to be evenly divided between biliary and renal routes. The biologic half-life of glyburide is not significantly correlated with renal function in subjects with creatinine clearances of 30 ml/minute/1.7 m2 or more. Gradations in disease state, multiple sites of sulfonylurea action, and inter-patient variability have made it difficult to relate biologic response to glyburide serum levels.

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.