Tonbac

Tonbac is indicated as an adjunct to diet and exercise to improve glycemic control in adults with type 2 diabetes  mellitus.

Limitations Of Use

Tonbac is not recommended for the treatment of type 1 diabetes mellitus or diabetic ketoacidosis.

Recommended Dosing

Tonbac should be administered orally with breakfast or the first main meal of the day.

The recommended starting dose of Tonbac is 5 mg once daily. Start patients at increased risk for hypoglycemia (e.g. the elderly or patients with hepatic insufficiency) at 2.5 mg.

Dosage adjustment can be made based on the patient's glycemic control. The maximum recommended dose is 20 mg once daily.

Patients receiving immediate release glipizide may be switched to Tonbac once daily at the nearest equivalent total daily dose.

Use With Other Glucose Lowering Agents

When adding Tonbac to other anti-diabetic drugs, initiate Tonbac at 5 mg once daily. Start patients at increased risk for hypoglycemia at a lower dose.

When colesevelam is coadministered with glipizide ER, maximum plasma concentration and total exposure to glipizide is reduced. Therefore, Tonbac should be administered at least 4 hours prior to colesevelam.

Glipizide is contraindicated in patients with:

• Known hypersensitivity to glipizide or any of the product's ingredients.
• Hypersensitivity to sulfonamide derivatives.

WARNINGS

Included as part of the PRECAUTIONS section.

PRECAUTIONS

Hypoglycemia

All sulfonylurea drugs, including Tonbac, are capable of producing severe hypoglycemia. Concomitant use of Tonbac with other anti-diabetic medication can increase the risk of hypoglycemia. A lower dose of Tonbac may be required to minimize the risk of hypoglycemia when combining it with other anti-diabetic medications.

Educate patients to recognize and manage hypoglycemia. When initiating and increasing Tonbac in patients who may be predisposed to hypoglycemia (e.g., the elderly, patients with renal impairment, patients on other anti-diabetic medications) start at 2.5 mg. Debilitated or malnourished patients, and those with adrenal, pituitary, or hepatic impairment are particularly susceptible to the hypoglycemic action of anti-diabetic medications. Hypoglycemia is also more likely to occur when caloric intake is deficient, after severe or prolonged exercise, or when alcohol is ingested.

The patient's ability to concentrate and react may be impaired as a result of hypoglycemia. Early warning symptoms of hypoglycemia may be different or less pronounced in patients with autonomic neuropathy, the elderly, and in patients who are taking beta-adrenergic blocking medications or other sympatholytic agents. These situations may result in severe hypoglycemia before the patient is aware of the hypoglycemia.

These impairments may present a risk in situations where these abilities are especially important, such as driving or operating other machinery. Severe hypoglycemia can lead to unconsciousness or convulsions and may result in temporary or permanent impairment of brain function or death.

Hemolytic Anemia

Treatment of patients with glucose 6-phosphate dehydrogenase (G6PD) deficiency with sulfonylurea agents, including GLUCOTROL XL, can lead to hemolytic anemia. Avoid use of Tonbac in patients with G6PD deficiency. In post marketing reports, hemolytic anemia has also been reported in patients who did not have known G6PD deficiency.

Increased Risk Of Cardiovascular Mortality With Sulfonylureas

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 type 2 diabetes mellitus. The study involved 823 patients who were randomly assigned to one of four treatment groups.

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 glipizide 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.

Macrovascular Outcomes

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

Gastrointestinal Obstruction

There have been reports of obstructive symptoms in patients with known strictures in association with the ingestion of another drug with this non-dissolvable extended release formulation. Avoid use of Tonbac in patients with preexisting severe gastrointestinal narrowing (pathologic or iatrogenic).

Patient Counseling Information

Advise the patient to read the FDA-approved patient labeling (PATIENT INFORMATION).

Inform patients of the potential adverse reactions of Tonbac including hypoglycemia. Explain the risks of hypoglycemia, its symptoms and treatment, and conditions that predispose to its development to patients and responsible family members. Also inform patients about the importance of adhering to dietary instructions, of a regular exercise program, and of regular testing of glycemic control.

Inform patients that GLUCOTROL XL should be swallowed whole. Inform patients that they should not chew, divide or crush tablets and they may occasionally notice in their stool something that looks like a tablet. In the Tonbac tablet, the medication is contained within a non-dissolvable shell that has been specially designed to slowly release the drug so the body can absorb it.

Advise patients with diabetes to inform their healthcare provider if they are pregnant, contemplating pregnancy, breastfeeding, or contemplating breastfeeding.

This product's label may have been updated. For full prescribing information, please visit www.pfizer.com.

Nonclinical Toxicology

Carcinogenesis, Mutagenesis, Impairment Of Fertility

A twenty month study in rats and an eighteen month study in mice at doses up to 75 times the maximum human dose revealed no evidence of drug-related carcinogenicity. Bacterial and in vivo mutagenicity tests were uniformly negative. Studies in rats of both sexes at doses up to 75 times the human dose showed no effects on fertility.

Use In Specific Populations

Pregnancy

Pregnancy Category C

Glipizide was found to be mildly fetotoxic in rat reproductive studies at all dose levels (5–50 mg/kg). This fetotoxicity has been similarly noted with other sulfonylureas, such as tolbutamide and tolazamide. The effect is perinatal and believed to be directly related to the pharmacologic (hypoglycemic) action of glipizide. There are no adequate and well controlled studies in pregnant women. Tonbac should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Nonteratogenic Effects

Prolonged severe hypoglycemia (4 to 10 days) has been reported in neonates born to mothers who were receiving a sulfonylurea drug at the time of delivery. This has been reported more frequently with the use of agents with prolonged half-lives. If glipizide is used during pregnancy, it should be discontinued at least one month before the expected delivery date.

Nursing Mothers

It is not known whether Tonbac is excreted in human milk. Because the potential for hypoglycemia in nursing infants may exist, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.

Pediatric Use

Safety and effectiveness in children have not been established.

Geriatric Use

There were no overall differences in effectiveness or safety between younger and older patients, but greater sensitivity of some individuals cannot be ruled out. Elderly patients are particularly susceptible to the hypoglycemic action of anti-diabetic agents. Hypoglycemia may be difficult to recognize in these patients. Therefore, dosing should be conservative to avoid hypoglycemia.

Hepatic Impairment

There is no information regarding the effects of hepatic impairment on the disposition of glipizide. However, since glipizide is highly protein bound and hepatic biotransformation is the predominant route of elimination, the pharmacokinetics and/or pharmacodynamics of glipizide may be altered in patients with hepatic impairment. If hypoglycemia occurs in such patients, it may be prolonged and appropriate management should be instituted.

The following serious adverse reactions are discussed in more detail below and elsewhere in the labeling:

• Hypoglycemia
• Hemolytic anemia

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

In clinical trials, 580 patients from 31 to 87 years of age received Tonbac in doses from 5 mg to 60 mg in both controlled and open trials. The dosages above 20 mg are not recommended dosages. In these trials, approximately 180 patients were treated with Tonbac for at least 6 months.

Table 1 summarizes the incidence of adverse reactions, other than hypoglycemia, that were reported in pooled double-blind, placebo-controlled trials in ≥3% of Tonbac-treated patients and more commonly than in patients who received placebo.

Table 1: Incidence (%) of Adverse Reactions Reported in ≥3% of Patients Treated in Placebo-Controlled Clinical Trials and More Commonly in Patients Treated with Tonbac (Excluding Hypoglycemia)

Hypoglycemia

Of the 580 patients that received Tonbac in clinical trials, 3.4% had hypoglycemia documented by a blood-glucose measurement <60 mg/dL and/or symptoms believed to be associated with hypoglycemia and 2.6% of patients discontinued for this reason. Hypoglycemia was not reported for any placebo patients.

Gastrointestinal Reactions

In clinical trials, the incidence of gastrointestinal (GI) side effects (nausea, vomiting, constipation, dyspepsia), occurred in less than 3% of Tonbac-treated patients and were more common in Tonbac-treated patients than those receiving placebo.

Dermatologic Reactions

In clinical trials, allergic skin reactions, i.e., urticaria occurred in less than 1.5% of treated patients and were more common in Tonbac treated patients than those receiving placebo. These may be transient and may disappear despite continued use of glipizide XL; if skin reactions persist, the drug should be discontinued.

Laboratory Tests

Mild to moderate elevations of ALT, LDH, alkaline phosphatase, BUN and creatinine have been noted. The relationship of these abnormalities to glipizide is uncertain.

Postmarketing Experience

The following adverse reactions have been identified during post approval use of Tonbac. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

• Abdominal pain
• Cholestatic and hepatocellular forms of liver injury accompanied by jaundice
• Leukopenia, agranulocytosis, thrombocytopenia, hemolytic anemia , aplastic anemia, pancytopenia
• Hepatic porphyria and disulfiram-like reactions
• Hyponatremia and the syndrome of inappropriate antidiuretic hormone (SIADH) secretion
• Rash
• There have been reports of gastrointestinal irritation and gastrointestinal bleeding with use of another drug with this non dissolvable extended release formulation.

Overdosage of sulfonylureas including Tonbac can produce severe hypoglycemia. Mild hypoglycemic symptoms without loss of consciousness or neurologic findings should be treated with oral glucose. Severe hypoglycemic reactions with coma, seizure, or other neurological impairment are medical emergencies requiring immediate treatment. The patient should be treated with glucagon or intravenous glucose. Patients should be closely monitored for a minimum of 24 to 48 hours since hypoglycemia may recur after apparent clinical recovery. Clearance of glipizide from plasma may be prolonged in persons with liver disease. Because of the extensive protein binding of glipizide, dialysis is unlikely to be of benefit.

The insulinotropic response to a meal is enhanced with Tonbac administration in diabetic patients. The postprandial insulin and C-peptide responses continue to be enhanced after at least 6 months of treatment. In two randomized, double-blind, dose-response studies comprising a total of 347 patients, there was no significant increase in fasting insulin in all Tonbac-treated patients combined compared to placebo, although minor elevations were observed at some doses.

In studies of Tonbac in subjects with type 2 diabete mellitus, once daily administration produced reductions in hemoglobin A1c, fasting plasma glucose and postprandial glucose. The relationship between dose and reduction in hemoglobin A1c was not established, however subjects treated with 20 mg had a greater reduction in fasting plasma glucose compared to subjects treated with 5 mg.

Absorption

The absolute bioavailability of glipizide was 100% after single oral doses in patients with type 2 diabetes mellitus. Beginning 2 to 3 hours after administration of Tonbac, plasma drug concentrations gradually rise reaching maximum concentrations within 6 to 12 hours after dosing. With subsequent once daily dosing of Tonbac, plasma glipizide concentrations are maintained throughout the 24 hour dosing interval with less peak to trough fluctuation than that observed with twice daily dosing of immediate release glipizide.

The mean relative bioavailability of glipizide in 21 males with type 2 diabetes mellitus after administration of 20 mg Tonbac, compared to immediate release Glucotrol (10 mg given twice daily), was 90% at steady-state. Steady-state plasma concentrations were achieved by at least the fifth day of dosing with Tonbac in 21 males with type 2 diabetes mellitus and patients younger than 65 years. No accumulation of drug was observed in patients with type 2 diabetes mellitus during chronic dosing with Tonbac.

Administration of Tonbac with food has no effect on the 2 to 3 hour lag time in drug absorption. In a single dose, food effect study in 21 healthy male subjects, the administration of Tonbac immediately before a high fat breakfast resulted in a 40% increase in the glipizide mean Cmax value, which was significant, but the effect on the AUC was not significant. There was no change in glucose response between the fed and fasting state. Markedly reduced GI retention times of the Tonbac tablets over prolonged periods (e.g., short bowel syndrome) may influence the pharmacokinetic profile of the drug and potentially result in lower plasma concentrations.

In a multiple dose study in 26 males with type 2 diabetes mellitus, the pharmacokinetics of glipizide were linear with Tonbac in that the plasma drug concentrations increased proportionately with dose. In a single dose study in 24 healthy subjects, four 5-mg, two 10-mg, and one 20-mg Tonbac tablets were bioequivalent. In a separate single dose study in 36 healthy subjects, four 2.5-mg Tonbac tablets were bioequivalent to one 10-mg Tonbac tablet.

Distribution

The mean volume of distribution was approximately 10 liters after single intravenous doses in patients with type 2 diabetes mellitus. Glipizide is 98–99% bound to serum proteins, primarily to albumin.

Metabolism

The major metabolites of glipizide are products of aromatic hydroxylation and have no hypoglycemic activity. A minor metabolite, an acetylamino-ethyl benzene derivative, which accounts for less than 2% of a dose, is reported to have 1/10 to 1/3 as much hypoglycemic activity as the parent compound.

Elimination

Glipizide is eliminated primarily by hepatic biotransformation: less than 10% of a dose is excreted as unchanged drug in urine and feces; approximately 90% of a dose is excreted as biotransformation products in urine (80%) and feces (10%). The mean total body clearance of glipizide was approximately 3 liters per hour after single intravenous doses in patients with type 2 diabetes mellitus. The mean terminal elimination half-life of glipizide ranged from 2 to 5 hours after single or multiple doses in patients with type 2 diabetes mellitus.