Prescription Drug Information: Glyburide

GLYBURIDE- glyburide tablet
NuCare Pharmceuticals,Inc.

DESCRIPTION

Glyburide Tablets, USP are an oral blood-glucose-lowering drug of the sulfonylurea class. It is a white, crystalline compound, formulated as tablets of 1.25 mg, 2.5 mg, and 5 mg strengths for oral administration. Glyburide Tablets, USP contain the active ingredient glyburide and the following inactive ingredients: dibasic calcium phosphate anhydrous USP, dibasic calcium phosphate dihydrate USP, magnesium stearate NF, microcrystalline cellulose NF, sodium alginate NF, talc USP. Glyburide Tablets USP, 1.25 mg also contain FD&C Yellow #6 Aluminum Lake. Glyburide Tablets USP, 2.5 mg also contain D&C Red #27 Aluminum Lake. Glyburide Tablets USP, 5 mg also contain FD&C Blue #1 Aluminum Lake. Chemically, glyburide is identified as 1-[[p-[2-(5-Chloro-o-anisamido)ethyl]phenyl]sulfonyl]-3-cyclohexylurea.

The CAS Registry Number is 10238-21-8.

The structural formula is:

Structural Formula
(click image for full-size original)

The molecular weight is 493.99. The aqueous solubility of glyburide increases with pH as a result of salt formation.

CLINICAL PHARMACOLOGY

Glyburide appears to lower the blood glucose acutely by stimulating the release of insulin from the pancreas, an effect dependent upon functioning beta cells in the pancreatic islets. The mechanism by which glyburide lowers blood glucose during long-term administration has not been clearly established.

With chronic administration in Type II diabetic patients, the blood glucose lowering effect persists despite a gradual decline in the insulin secretory response to the drug. Extrapancreatic effects may play a part in the mechanism of action of oral sulfonylurea hypoglycemic drugs.

In addition to its blood glucose lowering actions, glyburide produces a mild diuresis by enhancement of renal free water clearance. Clinical experience to date indicates an extremely low incidence of disulfiram-like reactions in patients while taking glyburide tablets.

Pharmacokinetics

Single-dose studies with glyburide tablets in normal subjects demonstrate significant absorption within one hour, peak drug levels at about four hours, and low but detectable levels at twenty-four hours. Mean serum levels of glyburide, as reflected by areas under the serum concentration-time curve, increase in proportion to corresponding increases in dose. Multiple-dose studies with glyburide tablets in diabetic patients demonstrate drug level concentration-time curves similar to single-dose studies, indicating no build-up of drug in tissue depots. The decrease of glyburide in the serum of normal healthy individuals is biphasic, the terminal half-life being about 10 hours. In single-dose studies in fasting normal subjects, the degree and duration of blood glucose lowering is proportional to the dose administered and to the area under the drug level concentration-time curve. The blood glucose lowering effect persists for 24 hours following single morning doses in non-fasting diabetic patients. Under conditions of repeated administration in diabetic patients, however, there is no reliable correlation between blood drug levels and fasting blood glucose levels. A one-year study of diabetic patients treated with glyburide showed no reliable correlation between administered dose and serum drug level.

The major metabolite of glyburide is the 4-trans-hydroxy derivative. A second metabolite, the 3-cis-hydroxy derivative, also occurs. These metabolites contribute no significant hypoglycemic action since they are only weakly active (1/400th and 1/40th, respectively, as glyburide) in rabbits.

Glyburide is excreted as metabolites in the bile and urine, approximately 50% by each route. This dual excretory pathway is qualitatively different from that of other sulfonylureas, which are excreted primarily in the urine.

Sulfonylurea drugs are extensively bound to serum proteins. Displacement from protein binding sites by other drugs may lead to enhanced hypoglycemic action. In vitro , the protein binding exhibited by glyburide is predominantly non-ionic, whereas that of other sulfonylureas (chlorpropamide, tolbutamide, tolazamide) is predominantly ionic. Acidic drugs such as phenylbutazone, warfarin, and salicylates displace the ionic-binding sulfonylureas from serum proteins to a far greater extent than the non-ionic binding glyburide. It has not been shown that this difference in protein binding will result in fewer drug-drug interactions with glyburide in clinical use.

INDICATIONS AND USAGE

Glyburide Tablets, USP are indicated as an adjunct to diet and exercise to improve glycemic control in adults with type 2 diabetes mellitus.

CONTRAINDICATIONS

Glyburide tablets are contraindicated in patients:

1. With known hypersensitivity to the drug or any of its excipients.
2. With type 1 diabetes mellitus or diabetic ketoacidosis, with or without coma.
These conditions should be treated with insulin.
3. Treated with bosentan.

WARNINGS

SPECIAL WARNING ON INCREASED RISK OF CARDIOVASCULAR MORTALITY

The administration of oral hypoglycemic drugs has been reported to be associated with increased cardiovascular mortality as compared to treatment with diet alone or diet plus insulin. This warning is based on the study conducted by the University Group Diabetes Program (UGDP), a long-term prospective clinical trial designed to evaluate the effectiveness of glucose-lowering drugs in preventing or delaying vascular complications in patients with non-insulin-dependent diabetes. The study involved 823 patients who were randomly assigned to one of four treatment groups ( Diabetes 19 (supp. 2): 747–830, 1970).

UGDP reported that patients treated for 5 to 8 years with diet plus a fixed dose of tolbutamide (1.5 grams per day) had a rate of cardiovascular mortality approximately 2½ times that of patients treated with diet alone. A significant increase in total mortality was not observed, but the use of tolbutamide was discontinued based on the increase in cardiovascular mortality, thus limiting the opportunity for the study to show an increase in overall mortality. Despite controversy regarding the interpretation of these results, the findings of the UGDP study provide an adequate basis for this warning. The patient should be informed of the potential risks and advantages of glyburide and of alternative modes of therapy.

Although only one drug in the sulfonylurea class (tolbutamide) was included in this study, it is prudent from a safety standpoint to consider that this warning may also apply to other oral hypoglycemic drugs in this class, in view of their close similarities in mode of action and chemical structure.

Persons allergic to other sulfonamide derivatives may develop an allergic reaction to glyburide as well.

PRECAUTIONS

General

Macrovascular Outcomes: There have been no clinical studies establishing conclusive evidence of macrovascular risk reduction with glyburide or any other anti-diabetic drug.

Hypoglycemia: All sulfonylurea drugs are capable of producing severe hypoglycemia. Proper patient selection, dosage, and instructions are important to avoid hypoglycemic episodes. Severe renal or hepatic insufficiency may cause elevated blood levels of glyburide and the latter may also diminish gluconeogenic capacity, both of which increase the risk of serious, prolonged hypoglycemic reactions. Elderly, debilitated or malnourished patients, and those with adrenal or pituitary insufficiency are particularly susceptible to the hypoglycemic action of glucose-lowering drugs. Hypoglycemia may be difficult to recognize in patients with autonomic neuropathy, the elderly, and in people who are taking beta-adrenergic blocking drugs or other sympatholytic agents.

Hypoglycemia is more likely to occur when caloric intake is deficient, after severe or prolonged exercise, when alcohol is ingested, or when more than one glucose-lowering drug is used. Loss of control of blood glucose: When a patient stabilized on any diabetic regimen is exposed to stress such as fever, trauma, infection, or surgery, a loss of control may occur. At such times, it may be necessary to discontinue glyburide and administer insulin.

The effectiveness of any oral hypoglycemic drug, including glyburide, in lowering blood glucose to a desired level decreases in many patients over a period of time, which may be due to progression of the severity of the diabetes or to diminished responsiveness to the drug. This phenomenon is known as secondary failure, to distinguish it from primary failure in which the drug is ineffective in an individual patient when first given.

Hemolytic Anemia: Treatment of patients with glucose 6-phosphate dehydrogenase (G6PD) deficiency with sulfonylurea agents can lead to hemolytic anemia. Because glyburide belongs to the class of sulfonylurea agents, caution should be used in patients with G6PD deficiency and a non-sulfonylurea alternative should be considered. In postmarketing reports, hemolytic anemia has also been reported in patients who did not have known G6PD deficiency.

Information for Patients

Patients should be informed of the potential risks and advantages of glyburide tablets and of alternative modes of therapy. They should also be informed about the importance of adherence to dietary instructions, of a regular exercise program, and of regular testing of blood glucose.

The risks of hypoglycemia, its symptoms and treatment, and conditions that predispose to its development should be explained to patients and responsible family members. Primary and secondary failure should also be explained.

Laboratory Tests

Periodic fasting blood glucose measurements should be performed to monitor therapeutic response. A glycosylated hemoglobin determination should also be performed periodically.

Drug Interactions

The hypoglycemic action of sulfonylureas may be potentiated by certain drugs including nonsteroidal anti-inflammatory agents, ACE inhibitors, disopyramide, fluoxetine, clarithromycin, and other drugs that are highly protein bound, salicylates, sulfonamides, chloramphenicol, probenecid, monoamine oxidase inhibitors, and beta adrenergic blocking agents. When such drugs are administered to a patient receiving glyburide tablets, the patient should be observed closely for hypoglycemia. When such drugs are withdrawn from a patient receiving glyburide tablets, the patient should be observed closely for loss of control.

An increased incidence of elevated liver enzymes was observed in patients receiving glyburide concomitantly with bosentan. Therefore concomitant administration of glyburide and bosentan is contraindicated (see CONTRAINDICATIONS).

A potential interaction between oral miconazole and oral hypoglycemic agents leading to severe hypoglycemia has been reported. Whether this interaction also occurs with the intravenous, topical or vaginal preparations of miconazole is not known.

A possible interaction between glyburide and fluoroquinolone antibiotics has been reported resulting in a potentiation of the hypoglycemic action of glyburide. The mechanism for this interaction is not known.

Possible interactions between glyburide and coumarin derivatives have been reported that may either potentiate or weaken the effects of coumarin derivatives. The mechanism of these interactions is not known.

Rifampin may worsen glucose control of glyburide because rifampin can significantly induce metabolic isozymes of glyburide such as CYP2C9 and 3A4.

Certain drugs tend to produce hyperglycemia and may lead to loss of control. These drugs include the thiazides and other diuretics, corticosteroids, phenothiazines, thyroid products, estrogens, oral contraceptives, phenytoin, nicotinic acid, sympathomimetics, calcium channel blocking drugs, and isoniazid. When such drugs are administered to a patient receiving glyburide tablets, the patient should be closely observed for loss of control. When such drugs are withdrawn from a patient receiving glyburide tablets, the patient should be observed closely for hypoglycemia.

Glyburide may increase cyclosporine plasma concentration and potentially lead to its increased toxicity. Monitoring and dosage adjustment of cyclosporine are therefore recommended when both drugs are coadministered.

Colesevelam: Concomitant administration of colesevelam and glyburide resulted in reductions in glyburide AUC and C max of 32% and 47%, respectively. When glyburide was administered 1 hour before colesevelam, the reductions in glyburide AUC and C max were 20% and 15%, respectively, and not significantly changed (-7% and 4%, respectively) when administered 4 hours before colesevelam. Therefore, glyburide should be administered at least 4 hours prior to colesevelam.

Glyburide is mainly metabolized by CYP 2C9 and to a lesser extent by CYP 3A4. There is a potential for drug-drug interaction when glyburide is coadministered with inducers or inhibitors of CYP 2C9, which should be taken into account when considering concomitant therapy.

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