Tai Bi

Tai Bi (Glyburide and Metformin HCl) Tablets is indicated as an adjunct to diet and exercise to improve glycemic control in adults with type 2 diabetes mellitus.

General Considerations

Dosage of Tai Bi must be individualized on the basis of both effectiveness and tolerance while not exceeding the maximum recommended daily dos e of 20 mg glyburide/2000 mg metformin. Tai Bi should be given with meals and should be initiated at a low dose, with gradual dose escalation as described below, in order to avoid hypoglycemia (largely due to glyburide), reduce GI side effects (largely due to metformin), and permit determination of the minimum effective dose for adequate control of blood glucose for the individual patient.

With initial treatment and during dose titration, appropriate blood glucose monitoring should be used to determine the therapeutic response to Tai Bi and to identify the minimum effective dose for the patient. Thereafter, HbA1c should be measured at intervals of approximately 3 months to assess the effectiveness of therapy. The therapeutic goal in all patients with type 2 diabetes is to decrease FPG, PPG, and HbA1c to normal or as near normal as possible. Ideally, the response to therapy should be evaluated using HbA (glycosylated hemoglobin), which is a better indicator of long-term glycemic control than FPG alone.

No studies have been performed specifically examining the safety and efficacy of switching to Tai Bi therapy in patients taking concomitant glyburide (or other sulfonylurea) plus metformin. Changes in glycemic control may occur in such patients, with either hyperglycemia or hypoglycemia possible. Any change in therapy of type 2 diabetes should be undertaken with care and appropriate monitoring.

Tai Bi in Patients with Inadequate Glycemic Control on Diet and Exercise

Recommended starting dose: 1.25 mg/250 mg once or twice daily with meals.

For patients with type 2 diabetes whose hyperglycemia cannot be satisfactorily managed with diet and exercise alone, the recommended starting dose of Tai Bi is 1.25 mg/250 mg once a day with a meal. As initial therapy in patients with baseline HbA1c > 9% or an FPG > 200 mg/dL, a starting dose of Tai Bi 1.25 mg/250 mg twice daily with the morning and evening meals may be used. Dosage increases should be made in increments of 1.25 mg/250 mg per day every 2 weeks up to the minimum effective dose necessary to achieve adequate control of blood glucose. In clinical trials of Tai Bi as initial therapy, there was no experience with total daily doses > 10 mg/2000 mg per day. Tai Bi 5 mg/500 mg should not be used as initial therapy due to an increased risk of hypoglycemia.

Tai Bi Use in Patients with Inadequate Glycemic Control on a Sulfonylurea and/or Metformin

Recommended starting dose: 2.5 mg/500 mg or 5 mg/500 mg twice daily with meals.

For patients not adequately controlled on either glyburide (or another sulfonylurea) or metformin alone, the recommended starting dose of Tai Bi is 2.5 mg/500 mg or 5 mg/500 mg twice daily with the morning and evening meals. In order to avoid hypoglycemia, the starting dose of Tai Bi should not exceed the daily doses of glyburide or metformin already being taken. The daily dose should be titrated in increments of no more than 5 mg/500 mg up to the minimum effective dose to achieve adequate control of blood glucose or to a maximum dose of 20 mg/2000 mg per day.

For patients previously treated with combination therapy of glyburide (or another sulfonylurea) plus metformin, if switched to Tai Bi, the starting dose should not exceed the daily dose of glyburide (or equivalent dose of another sulfonylurea) and metformin already being taken. Patients should be monitored closely for signs and symptoms of hypoglycemia following such a switch and the dose of Tai Bi should be titrated as described above to achieve adequate control of blood glucose.

Addition Of Thiazolidinediones To Tai Bi Therapy

For patients not adequately controlled on Tai Bi, a thiazolidinedione can be added to Tai Bi therapy. When a thiazolidinedione is added to Tai Bi therapy, the current dose of Tai Bi can be continued and the thiazolidinedione initiated at its recommended starting dose. For patients needing additional glycemic control, the dose of the thiazolidinedione can be increased based on its recommended titration schedule. The increased glycemic control attainable with Tai Bi plus a thiazolidinedione may increase the potential for hypoglycemia at any time of day. In patients who develop hypoglycemia when receiving Tai Bi and a thiazolidinedione, consideration should be given to reducing the dose of the glyburide component of Tai Bi. As clinically warranted, adjustment of the dosages of the other components of the antidiabetic regimen should also be considered.

Patients Receiving Colesevelam

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

Specific Patient Populations

Tai Bi is not recommended for use during pregnancy. The initial and maintenance dosing of Tai Bi should be conservative in patients with advanced age, due to the potential for decreased renal function in this population. Any dosage adjustment requires a careful assessment of renal function. Generally, elderly, debilitated, and malnourished patients should not be titrated to the maximum dose of Tai Bi to avoid the risk of hypoglycemia. Monitoring of renal function is necessary to aid in prevention of metformin-associated lactic acidosis, particularly in the elderly. (See WARNINGS.)

Tai Bi is contraindicated in patients with:

1. Renal disease or renal dysfunction (eg, as suggested by serum creatinine levels ≥ 1.5 mg/dL [males], ≥ 1.4 mg/dL [females], or abnormal creatinine clearance) which may also result from conditions such as cardiovascular collapse (shock), acute myocardial infarction, and septicemia (see WARNINGS and PRECAUTIONS).
2. Known hypersensitivity to metformin hydrochloride or glyburide.
3. Acute or chronic metabolic acidosis, including diabetic ketoacidosis, with or without coma. Diabetic ketoacidosis should be treated with insulin.
4. Concomitant administration of bosentan.

Tai Bi should be temporarily discontinued in patients undergoing radiologic studies involving intravascular administration of iodinated contrast materials, because use of such products may result in acute alteration of renal function. (See also PRECAUTIONS.)

WARNINGS

Metformin Hydrochloride

Lactic Acidosis

Lactic acidosis is a rare, but serious, metabolic complication that can occur due to metformin accumulation during treatment with Tai Bi (Glyburide and Metformin HCl) Tablets; when it occurs, it is fatal in approximately 50% of cases. Lactic acidosis may also occur in association with a number of pathophysiologic conditions, including diabetes mellitus, and whenever there is significant tissue hypoperfusion and hypoxemia. Lactic acidosis is characterized by elevated blood lactate levels ( > 5 mmol/L), decreased blood pH, electrolyte disturbances with an increased anion gap, and an increased lactate/pyruvate ratio. When metformin is implicated as the cause of lactic acidosis, metformin plasma levels > 5 μg/mL are generally found.

The reported incidence of lactic acidosis in patients receiving metformin hydrochloride is very low (approximately 0.03 cases /1000 patient-years, with approximately 0.015 fatal cases /1000 patient-years ). In more than 20,000 patient-years exposure to metformin in clinical trials, there were no reports of lactic acidosis. Reported cases have occurred primarily in diabetic patients with significant renal insufficiency, including both intrinsic renal disease and renal hypoperfusion, often in the setting of multiple concomitant medical/surgical problems and multiple concomitant medications. Patients with congestive heart failure requiring pharmacologic management, in particular those with unstable or acute congestive heart failure who are at risk of hypoperfusion and hypoxemia, are at increased risk of lactic acidosis. The risk of lactic acidosis increases with the degree of renal dysfunction and the patient's age. The risk of lactic acidosis may, therefore, be significantly decreased by regular monitoring of renal function in patients taking metformin and by use of the minimum effective dose of metformin. In particular, treatment of the elderly should be accompanied by careful monitoring of renal function. Tai Bi treatment should not be initiated in patients ≥ 80 years of age unless measurement of creatinine clearance demonstrates that renal function is not reduced, as these patients are more susceptible to developing lactic acidosis. In addition, Tai Bi should be promptly withheld in the presence of any condition associated with hypoxemia, dehydration, or sepsis. Because impaired hepatic function may significantly limit the ability to clear lactate, Tai Bi should generally be avoided in patients with clinical or laboratory evidence of hepatic disease. Patients should be cautioned against excessive alcohol intake, either acute or chronic, when taking Tai Bi, since alcohol potentiates the effects of metformin hydrochloride on lactate metabolism. In addition, Tai Bi should be temporarily discontinued prior to any intravascular radiocontrast study and for any surgical procedure (see also PRECAUTIONS).

The onset of lactic acidosis often is subtle, and accompanied only by nonspecific symptoms such as malaise, myalgias, respiratory distress, increasing somnolence, and nonspecific abdominal distress. There may be associated hypothermia, hypotension, and resistant bradyarrhythmias with more marked acidosis. The patient and the patient's physician must be aware of the possible importance of such symptoms and the patient should be instructed to notify the physician immediately if they occur (see also PRECAUTIONS). Tai Bi should be withdrawn until the situation is clarified. Serum electrolytes, ketones, blood glucose, and if indicated, blood pH, lactate levels , and even blood metformin levels may be useful. Once a patient is stabilized on any dos e level of Tai Bi, gastrointestinal symptoms , which are common during initiation of therapy with metformin, are unlikely to be drug related. Later occurrence of gastrointestinal symptoms could be due to lactic acidosis or other serious disease.

Levels of fasting venous plasma lactate above the upper limit of normal but less than 5 mmol/L in patients taking Tai Bi do not necessarily indicate impending lactic acidosis and may be explainable by other mechanisms, such as poorly controlled diabetes or obesity, vigorous physical activity, or technical problems in s ample handling. (See also PRECAUTIONS.)

Lactic acidosis should be suspected in any diabetic patient with metabolic acidosis lacking evidence of ketoacidosis (ketonuria and ketonemia).

Lactic acidosis is a medical emergency that must be treated in a hospital setting. In a patient with lactic acidosis who is taking Tai Bi, the drug should be discontinued immediately and general supportive measures promptly instituted. Because metformin hydrochloride is dialyzable (with a clearance of up to 170 mL/min under good hemodynamic conditions ), prompt hemodialysis is recommended to correct the acidosis and remove the accumulated metformin. Such management often results in prompt reversal of symptoms and recovery. (See also CONTRAINDICATIONS and PRECAUTIONS.)

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 glucoselowering drugs in preventing or delaying vascular complications in patients with non-insulindependent diabetes. The study involved 823 patients who were randomly assigned to 1 of 4 treatment groups (Diabetes 19 (Suppl. 2):747-830, 1970).

UGDP reported that patients treated for 5 to 8 years with diet plus a fixed dose of tolbutamide (1.5g 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 bas is for this warning. The patient should be informed of the potential risks and benefits of glyburide and of alternative modes of therapy.

Although only 1 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 hypoglycemic drugs in this class, in view of their close similarities in mode of action and chemical structure.

PRECAUTIONS

General

Macrovascular Outcomes

There have been no clinical studies establishing conclusive evidence of macrovascular risk reduction with Tai Bi or any other antidiabetic drug.

Tai Bi

Hypoglycemia

Tai Bi is capable of producing hypoglycemia or hypoglycemic symptoms, therefore, proper patient selection, dosing, and instructions are important to avoid potential hypoglycemic episodes. The risk of hypoglycemia is increased when caloric intake is deficient, when strenuous exercise is not compensated by caloric supplementation, or during concomitant use with other glucose-lowering agents or ethanol. Renal or hepatic insufficiency may cause elevated drug levels of both glyburide and metformin hydrochloride, and the hepatic insufficiency may also diminish gluconeogenic capacity, both of which increase the risk of hypoglycemic reactions. Elderly, debilitated, or malnourished patients and those with adrenal or pituitary insufficiency or alcohol intoxication are particularly susceptible to hypoglycemic effects. Hypoglycemia may be difficult to recognize in the elderly and people who are taking beta-adrenergic blocking drugs.

Glyburide

Hemolytic Anemia

Treatment of patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency with sulfonylurea agents can lead to hemolytic anemia. Because Tai Bi 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.

Metformin Hydrochloride

Monitoring of Renal Function

Metformin is known to be substantially excreted by the kidney, and the risk of metformin accumulation and lactic acidosis increases with the degree of impairment of renal function. Thus, patients with serum creatinine levels above the upper limit of normal for their age should not receive Tai Bi. In patients with advanced age, Tai Bi should be carefully titrated to establish the minimum dose for adequate glycemic effect, because aging is associated with reduced renal function. In elderly patients, particularly those ≥ 80 years of age, renal function should be monitored regularly and, generally, Tai Bi should not be titrated to the maximum dose (see WARNINGS and DOSAGE AND ADMINISTRATION). Before initiation of Tai Bi therapy and at least annually thereafter, renal function should be assessed and verified as normal. In patients in whom development of renal dysfunction is anticipated, renal function should be assessed more frequently and Tai Bi discontinued if evidence of renal impairment is present.

Use Of Concomitant Medications That May Affect Renal Function Or Metformin Disposition

Concomitant medication(s) that may affect renal function or result in significant hemodynamic change or may interfere with the disposition of metformin, such as cationic drugs that are eliminated by renal tubular secretion (see DRUG INTERACTIONS), should be used with caution.

Radiologic studies involving the use of intravascular iodinated contrast materials (for example, intravenous urogram, intravenous cholangiography, angiography, and computed tomography (CT) scans with intravascular contrast materials)

Intravascular contrast studies with iodinated materials can lead to acute alteration of renal function and have been associated with lactic acidosis in patients receiving metformin (see CONTRAINDICATIONS). Therefore, in patients in whom any such study is planned, Tai Bi should be temporarily discontinued at the time of or prior to the procedure, and withheld for 48 hours subsequent to the procedure and reinstituted only after renal function has been reevaluated and found to be normal.

Hypoxic States

Cardiovascular collapse (shock) from whatever cause, acute congestive heart failure, acute myocardial infarction, and other conditions characterized by hypoxemia have been associated with lactic acidosis and may also cause prerenal azotemia. When such events occur in patients on Tai Bi therapy, the drug should be promptly discontinued.

Surgical Procedures

Tai Bi therapy should be temporarily suspended for any surgical procedure (except minor procedures not associated with restricted intake of food and fluids) and should not be restarted until the patient's oral intake has resumed and renal function has been evaluated as normal.

Alcohol Intake

Alcohol is known to potentiate the effect of metformin on lactate metabolism. Patients, therefore, should be warned against excessive alcohol intake, acute or chronic, while receiving Tai Bi. Due to its effect on the gluconeogenic capacity of the liver, alcohol may also increase the risk of hypoglycemia.

Impaired Hepatic Function

Since impaired hepatic function has been associated with some cases of lactic acidosis, Tai Bi should generally be avoided in patients with clinical or laboratory evidence of hepatic disease.

Vitamin B12 Levels

In controlled clinical trials with metformin of 29 weeks duration, a decrease to subnormal levels of previously normal serum vitamin B12, without clinical manifestations, was observed in approximately 7% of patients. Such decrease, possibly due to interference with B12 absorption from the B12-intrinsic factor complex is, however, very rarely associated with anemia and appears to be rapidly reversible with discontinuation of metformin or vitamin B supplementation. Measurement of hematologic parameters on an annual basis is advised in patients on metformin and any apparent abnormalities should be appropriately investigated and managed (see PRECAUTIONS: Laboratory Tests ).

Certain individuals (those with inadequate vitamin B12 or calcium intake or absorption) appear to be predisposed to developing subnormal vitamin B12 levels. In these patients, routine serum vitamin B12 measurements at 2- to 3-year intervals may be useful.

Change In Clinical Status Of Patients With Previously Controlled Type 2 Diabetes

A patient with type 2 diabetes previously well controlled on metformin who develops laboratory abnormalities or clinical illness (especially vague and poorly defined illness) should be evaluated promptly for evidence of ketoacidosis or lactic acidosis. Evaluation should include serum electrolytes and ketones, blood glucose and, if indicated, blood pH, lactate, pyruvate, and metformin levels. If acidosis of either form occurs, Tai Bi must be stopped immediately and other appropriate corrective measures initiated (see also WARNINGS).

Addition of Thiazolidinediones to Tai Bi Therapy

Hypoglycemia

Patients receiving Tai Bi in combination with a thiazolidinedione may be at risk for hypoglycemia.

Weight Gain

Weight gain was seen with the addition of rosiglitazone to Tai Bi, similar to that reported for thiazolidinedione therapy alone.

Hepatic Effects

When a thiazolidinedione is used in combination with Tai Bi, periodic monitoring of liver function tests should be performed in compliance with the labeled recommendations for the thiazolidinedione.

Information For Patients

Tai Bi

Patients should be informed of the potential risks and benefits of Tai Bi and alternative modes of therapy. They should also be informed about the importance of adherence to dietary instructions; a regular exercise program; and regular testing of blood glucose, glycosylated hemoglobin, renal function, and hematologic parameters.

The risks of lactic acidosis associated with metformin therapy, its symptoms, and conditions that predispose to its development, as noted in the WARNINGS and PRECAUTIONS sections, should be explained to patients. Patients should be advised to discontinue Tai Bi immediately and promptly notify their health practitioner if unexplained hyperventilation, myalgia, malaise, unusual somnolence, or other nonspecific symptoms occur. Once a patient is stabilized on any dose level of Tai Bi, gastrointestinal symptoms, which are common during initiation of metformin therapy, are unlikely to be drug related. Later occurrence of gastrointestinal symptoms could be due to lactic acidosis or other serious disease.

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

Patients should be counseled against excessive alcohol intake, either acute or chronic, while receiving Tai Bi. (See PATIENT INFORMATION printed below.)

Laboratory Tests

Periodic fasting blood glucose (FBG) and HbA1c measurements should be performed to monitor therapeutic response.

Initial and periodic monitoring of hematologic parameters (eg, hemoglobin/hematocrit and red blood cell indices) and renal function (serum creatinine) should be performed, at least on an annual basis. While megaloblastic anemia has rarely been seen with metformin therapy, if this is suspected, vitamin B12 deficiency should be excluded.

Carcinogenesis, Mutagenesis, Impairment Of Fertility

No animal studies have been conducted with the combined products in Tai Bi. The following data are based on findings in studies performed with the individual products.

Glyburide

Studies in rats with glyburide alone at doses up to 300 mg/kg/day (approximately 145 times the maximum recommended human daily [MRHD] dose of 20 mg for the glyburide component of Tai Bi based on body surface area comparisons) for 18 months revealed no carcinogenic effects. In a 2-year oncogenicity study of glyburide in mice, there was no evidence of treatment-related tumors.

There was no evidence of mutagenic potential of glyburide alone in the following in vitro tests: Salmonella microsome test (Ames test) and in the DNA damage/alkaline elution assay.

Metformin Hydrochloride

Long-term carcinogenicity studies were performed with metformin alone in rats (dosing duration of 104 weeks) and mice (dosing duration of 91 weeks) at doses up to and including 900 mg/kg/day and 1500 mg/kg/day, respectively. These doses are both approximately 4 times the MRHD dose of 2000 mg of the metformin component of Tai Bi based on body surface area comparisons. No evidence of carcinogenicity with metformin alone was found in either male or female mice. Similarly, there was no tumorigenic potential observed with metformin alone in male rats. There was, however, an increased incidence of benign stromal uterine polyps in female rats treated with 900 mg/kg/day of metformin alone.

There was no evidence of a mutagenic potential of metformin alone in the following in vitro tests: Ames test (S. typhimurium), gene mutation test (mouse lymphoma cells), or chromosomal aberrations test (human lymphocytes). Results in the in vivo mouse micronucleus test were also negative.

Fertility of male or female rats was unaffected by metformin alone when administered at doses as high as 600 mg/kg/day, which is approximately 3 times the MRHD dose of the metformin component of Tai Bi based on body surface area comparisons.

Pregnancy

Teratogenic Effects

Pregnancy Category B

Recent information strongly suggests that abnormal blood glucose levels during pregnancy are associated with a higher incidence of congenital abnormalities. Most experts recommend that insulin be used during pregnancy to maintain blood glucose as close to normal as possible. Because animal reproduction studies are not always predictive of human response, Tai Bi should not be used during pregnancy unless clearly needed. (See below.)

There are no adequate and well-controlled studies in pregnant women with Tai Bi or its individual components. No animal studies have been conducted with the combined products in Tai Bi. The following data are based on findings in studies performed with the individual products.

Glyburide

Reproduction studies were performed in rats and rabbits at doses up to 500 times the MRHD dose of 20 mg of the glyburide component of Tai Bi based on body surface area comparisons and revealed no evidence of impaired fertility or harm to the fetus due to glyburide.

Metformin Hydrochloride

Metformin alone was not teratogenic in rats or rabbits at doses up to 600 mg/kg/day. This represents an exposure of about 2 and 6 times the MRHD dose of 2000 mg of the metformin component of Tai Bi based on body surface area comparisons for rats and rabbits, respectively. Determination of fetal concentrations demonstrated a partial placental barrier to metformin.

Nonteratogenic Effects

Prolonged severe hypoglycemia (4-10 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. It is not recommended that Tai Bi be used during pregnancy. However, if it is used, Tai Bi should be discontinued at least 2 weeks before the expected delivery date. (See Pregnancy: Teratogenic Effects : Pregnancy Category B.)

Nursing Mothers

Although it is not known whether glyburide is excreted in human milk, some sulfonylurea drugs are known to be excreted in human milk. Studies in lactating rats show that metformin is excreted into milk and reaches levels comparable to those in plasma. Similar studies have not been conducted in nursing mothers. Because the potential for hypoglycemia in nursing infants may exist, a decision should be made whether to discontinue nursing or to discontinue Tai Bi, taking into account the importance of the drug to the mother. If Tai Bi is discontinued, and if diet alone is inadequate for controlling blood glucose, insulin therapy should be considered.

Pediatric Use

The safety and efficacy of Tai Bi were evaluated in an active-controlled, double-blind, 26- week randomized trial involving a total of 167 pediatric patients (ranging from 9-16 years of age) with type 2 diabetes. Tai Bi was not shown statistically to be superior to either metformin or glyburide with respect to reducing HbA1c from baseline (see Table 5). No unexpected safety findings were associated with Tai Bi in this trial.

Table 5: HbA1c (Percent) Change From Baseline at 26 Weeks : Pediatric Study

Geriatric Use

Of the 642 patients who received Tai Bi in double-blind clinical studies, 23.8% were 65 and older while 2.8% were 75 and older. Of the 1302 patients who received Tai Bi in open-label clinical studies, 20.7% were 65 and older while 2.5% were 75 and older. No overall differences in effectiveness or safety were observed between these patients and younger patients, and other reported clinical experience has not identified differences in response between the elderly and younger patients, but greater sensitivity of some older individuals cannot be ruled out.

Metformin hydrochloride is known to be substantially excreted by the kidney and because the risk of serious adverse reactions to the drug is greater in patients with impaired renal function, Tai Bi should only be used in patients with normal renal function (see CONTRAINDICATIONS, WARNINGS, and CLINICAL PHARMACOLOGY: Pharmacokinetics ). Because aging is associated with reduced renal function, Tai Bi should be used with caution as age increases. Care should be taken in dose selection and should be based on careful and regular monitoring of renal function. Generally, elderly patients should not be titrated to the maximum dose of Tai Bi (see also WARNINGS and DOSAGE AND ADMINISTRATION).

Tai Bi

In double-blind clinical trials involving Tai Bi as initial therapy or as second-line therapy, a total of 642 patients received Tai Bi, 312 received metformin therapy, 324 received glyburide therapy, and 161 received placebo. The percent of patients reporting events and types of adverse events reported in clinical trials of Tai Bi (all strengths) as initial therapy and second-line therapy are listed in Table 6.

Table 6: Most Common Clinical Adverse Events ( > 5%) in Double-Blind Clinical Studies of Tai Bi Used as Initial or Second-Line Therapy

In a controlled clinical trial of rosiglitazone versus placebo in patients treated with Tai Bi (n=365), 181 patients received Tai Bi with rosiglitazone and 184 received Tai Bi with placebo.

Edema was reported in 7.7% (14/181) of patients treated with rosiglitazone compared to 2.2% (4/184) of patients treated with placebo. A mean weight gain of 3 kg was observed in rosiglitazone-treated patients.

Disulfiram-like reactions have very rarely been reported in patients treated with glyburide tablets.

Hypoglycemia

In controlled clinical trials of Tai Bi there were no hypoglycemic episodes requiring medical intervention and/or pharmacologic therapy; all events were managed by the patients. The incidence of reported symptoms of hypoglycemia (such as dizziness, shakiness, sweating, and hunger), in the initial therapy trial of Tai Bi are summarized in Table 7. The frequency of hypoglycemic symptoms in patients treated with Tai Bi 1.25 mg/250 mg was highest in patients with a baseline HbA1c < 7%, lower in those with a baseline HbA1c of between 7% and 8%, and was comparable to placebo and metformin in those with a baseline HbA1c > 8%. For patients with a baseline HbA1c between 8% and 11% treated with Tai Bi 2.5 mg/500 mg as initial therapy, the frequency of hypoglycemic symptoms was 30% to 35%. As second-line therapy in patients inadequately controlled on sulfonylurea alone, approximately 6.8% of all patients treated with Tai Bi experienced hypoglycemic symptoms. When rosiglitazone was added to Tai Bi therapy, 22% of patients reported 1 or more fingerstick glucose measurements ≤ 50 mg/dL compared to 3.3% of placebo-treated patients. All hypoglycemic events were managed by the patients and only 1 patient discontinued for hypoglycemia. (See PRECAUTIONS: General: Addition of Thiazolidinediones to Tai Bi Therapy.)

Gastrointestinal Reactions

The incidence of gastrointestinal (GI) side effects (diarrhea, nausea/vomiting, and abdominal pain) in the initial therapy trial are summarized in Table 7. Across all Tai Bi trials, GI symptoms were the most common adverse events with Tai Bi and were more frequent at higher dose levels.

In controlled trials, < 2% of patients discontinued Tai Bi therapy due to GI adverse events.

Table 7: Treatment Emergent Symptoms of Hypoglycemia or Gastrointestinal Adverse Events in a Placebo- and Active-Controlled Trial of Tai Bi as Initial Therapy

In postmarketing reports cholestatic jaundice and hepatitis may occur rarely which may progress to liver failure; Tai Bi should be discontinued if this occurs.

Glyburide

Overdosage of sulfonylureas, including glyburide tablets, can produce hypoglycemia. Mild hypoglycemic symptoms, without loss of consciousness or neurological findings, should be treated aggressively with oral glucose and adjustments in drug dosage and/or meal patterns. Close monitoring should continue until the physician is assured that the patient is out of danger. Severe hypoglycemic reactions with coma, seizure, or other neurological impairment occur infrequently, but constitute medical emergencies requiring immediate hospitalization. If hypoglycemic coma is diagnosed or suspected, the patient should be given a rapid intravenous injection of concentrated (50%) glucose solution. This should be followed by a continuous infusion of a more dilute (10%) glucose solution at a rate that will maintain the blood glucose at a level above 100 mg/dL. Patients should be closely monitored for a minimum of 24 to 48 hours, since hypoglycemia may recur after apparent clinical recovery.

Metformin Hydrochloride

Overdose of metformin hydrochloride has occurred, including ingestion of amounts > 50 g. Hypoglycemia was reported in approximately 10% of cases, but no causal association with metformin hydrochloride has been established. Lactic acidosis has been reported in approximately 32% of metformin overdose cases (see WARNINGS). Metformin is dialyzable with a clearance of up to 170 mL/min under good hemodynamic conditions. Therefore, hemodialysis may be useful for removal of accumulated drug from patients in whom metformin overdosage is suspected.

OVERDOSE

Glyburide

Overdosage of sulfonylureas, including glyburide tablets, can produce hypoglycemia. Mild hypoglycemic symptoms, without loss of consciousness or neurological findings, should be treated aggressively with oral glucose and adjustments in drug dosage and/or meal patterns. Close monitoring should continue until the physician is assured that the patient is out of danger. Severe hypoglycemic reactions with coma, seizure, or other neurological impairment occur infrequently, but constitute medical emergencies requiring immediate hospitalization. If hypoglycemic coma is diagnosed or suspected, the patient should be given a rapid intravenous injection of concentrated (50%) glucose solution. This should be followed by a continuous infusion of a more dilute (10%) glucose solution at a rate that will maintain the blood glucose at a level above 100 mg/dL. Patients should be closely monitored for a minimum of 24 to 48 hours, since hypoglycemia may recur after apparent clinical recovery.

Metformin Hydrochloride

Overdose of metformin hydrochloride has occurred, including ingestion of amounts > 50 g. Hypoglycemia was reported in approximately 10% of cases, but no causal association with metformin hydrochloride has been established. Lactic acidosis has been reported in approximately 32% of metformin overdose cases (see WARNINGS). Metformin is dialyzable with a clearance of up to 170 mL/min under good hemodynamic conditions. Therefore, hemodialysis may be useful for removal of accumulated drug from patients in whom metformin overdosage is suspected.

CONTRAINDICATIONS

Tai Bi is contraindicated in patients with:

1. Renal disease or renal dysfunction (eg, as suggested by serum creatinine levels ≥ 1.5 mg/dL [males], ≥ 1.4 mg/dL [females], or abnormal creatinine clearance) which may also result from conditions such as cardiovascular collapse (shock), acute myocardial infarction, and septicemia (see WARNINGS and PRECAUTIONS).
2. Known hypersensitivity to metformin hydrochloride or glyburide.
3. Acute or chronic metabolic acidosis, including diabetic ketoacidosis, with or without coma. Diabetic ketoacidosis should be treated with insulin.
4. Concomitant administration of bosentan.

Tai Bi should be temporarily discontinued in patients undergoing radiologic studies involving intravascular administration of iodinated contrast materials, because use of such products may result in acute alteration of renal function. (See also PRECAUTIONS.)

CLINICAL PHARMACOLOGY

Mechanism Of Action

Tai Bi combines glyburide and metformin hydrochloride, 2 antihyperglycemic agents with complementary mechanisms of action, to improve glycemic control in patients with type 2 diabetes.

Glyburide appears to lower 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 patients with type 2 diabetes, the blood glucose-lowering effect persists despite a gradual decline in the insulin secretory response to the drug. Extrapancreatic effects may be involved in the mechanism of action of oral sulfonylurea hypoglycemic drugs.

Metformin hydrochloride is an antihyperglycemic agent that improves glucose tolerance in patients with type 2 diabetes, lowering both basal and postprandial plasma glucose. Metformin hydrochloride decreases hepatic glucose production, decreases intestinal absorption of glucose, and improves insulin sensitivity by increasing peripheral glucose uptake and utilization.

Pharmacokinetics

Absorption And Bioavailability

Tai Bi

In bioavailability studies of Tai Bi 2.5 mg/500 mg and 5 mg/500 mg, the mean area under the plasma concentration versus time curve (AUC) for the glyburide component was 18% and 7%, respectively, greater than that of the Micronase® brand of glyburide coadministered with metformin. The glyburide component of Tai Bi, therefore, is not bioequivalent to Micronase®. The metformin component of Tai Bi is bioequivalent to metformin coadministered with glyburide.

Following administration of a single Tai Bi 5 mg/500 mg tablet with either a 20% glucose solution or a 20% glucose solution with food, there was no effect of food on the Cmax and a relatively small effect of food on the AUC of the glyburide component. The Tmax for the glyburide component was shortened from 7.5 hours to 2.75 hours with food compared to the same tablet strength administered fasting with a 20% glucose solution. The clinical significance of an earlier Tmax for glyburide after food is not known. The effect of food on the pharmacokinetics of the metformin component was indeterminate.

Glyburide

Single-dose studies with Micronase® tablets in normal subjects demonstrate significant absorption of glyburide within 1 hour, peak drug levels at about 4 hours, and low but detectable levels at 24 hours. Mean serum levels of glyburide, as reflected by areas under the serum concentration-time curve, increase in proportion to corresponding increases in dose. Bioequivalence has not been established between Tai Bi and single-ingredient glyburide products.

Metformin Hydrochloride

The absolute bioavailability of a 500 mg metformin hydrochloride tablet given under fasting conditions is approximately 50% to 60%. Studies using single oral doses of metformin tablets of 500 mg and 1500 mg, and 850 mg to 2550 mg, indicate that there is a lack of dose proportionality with increasing doses, which is due to decreased absorption rather than an alteration in elimination. Food decreases the extent of and slightly delays the absorption of metformin, as shown by approximately a 40% lower peak concentration and a 25% lower AUC in plasma and a 35-minute prolongation of time to peak plasma concentration following administration of a single 850 mg tablet of metformin with food, compared to the same tablet strength administered fasting. The clinical relevance of these decreases is unknown.

Distribution

Glyburide

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 results in fewer drug-drug interactions with glyburide tablets in clinical use.

Metformin Hydrochloride

The apparent volume of distribution (V/F) of metformin following single oral doses of 850 mg averaged 654±358 L. Metformin is negligibly bound to plasma proteins. Metformin partitions into erythrocytes, most likely as a function of time. At usual clinical doses and dosing schedules of metformin, steady state plasma concentrations of metformin are reached within 24 to 48 hours and are generally < 1 μg/mL. During controlled clinical trials, maximum metformin plasma levels did not exceed 5 μg/mL, even at maximum doses.

Metabolism And Elimination

Glyburide

The decrease of glyburide in the serum of normal healthy individuals is biphasic; the terminal half-life is about 10 hours. The major metabolite of glyburide is the 4-trans-hydroxy derivative. A second metabolite, the 3-cis-hydroxy derivative, also occurs. These metabolites probably contribute no significant hypoglycemic action in humans since they are only weakly active (1/400 and 1/40 as active, 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.

Metformin Hydrochloride

Intravenous single-dose studies in normal subjects demonstrate that metformin is excreted unchanged in the urine and does not undergo hepatic metabolism (no metabolites have been identified in humans) nor biliary excretion. Renal clearance (see Table 1) is approximately 3.5 times greater than creatinine clearance, which indicates that tubular secretion is the major route of metformin elimination. Following oral administration, approximately 90% of the absorbed drug is eliminated via the renal route within the first 24 hours, with a plasma elimination half-life of approximately 6.2 hours. In blood, the elimination half-life is approximately 17.6 hours, suggesting that the erythrocyte mass may be a compartment of distribution.

Special Populations

Patients With Type 2 Diabetes

Multiple-dose studies with glyburide in patients with type 2 diabetes demonstrate drug level concentration-time curves similar to single-dose studies, indicating no buildup of drug in tissue depots.

In the presence of normal renal function, there are no differences between single- or multiple-dose pharmacokinetics of metformin between patients with type 2 diabetes and normal subjects (see Table 1), nor is there any accumulation of metformin in either group at usual clinical doses.

Hepatic Insufficiency

No pharmacokinetic studies have been conducted in patients with hepatic insufficiency for either glyburide or metformin.

Renal Insufficiency

No information is available on the pharmacokinetics of glyburide in patients with renal insufficiency.

In patients with decreased renal function (based on creatinine clearance), the plasma and blood half-life of metformin is prolonged and the renal clearance is decreased in proportion to the decrease in creatinine clearance (see Table 1; also, see WARNINGS).

Geriatrics

There is no information on the pharmacokinetics of glyburide in elderly patients.

Limited data from controlled pharmacokinetic studies of metformin in healthy elderly subjects suggest that total plasma clearance is decreased, the half-life is prolonged, and Cmax is increased, when compared to healthy young subjects. From these data, it appears that the change in metformin pharmacokinetics with aging is primarily accounted for by a change in renal function (see Table 1). Metformin treatment should not be initiated in patients ≥ 80 years of age unless measurement of creatinine clearance demonstrates that renal function is not reduced.

Table 1: Select Mean (±SD) Metformin Pharmacokinetic Parameters Following Single or Multiple Oral Doses of Metformin

Pediatrics

After administration of a single oral GLUCOPHAGE® (metformin hydrochloride) 500 mg tablet with food, geometric mean metformin Cmax and AUC differed < 5% between pediatric type 2 diabetic patients (12-16 years of age) and gender- and weight-matched healthy adults (20-45 years of age), all with normal renal function.

After administration of a single oral Tai Bi tablet with food, dose-normalized geometric mean glyburide C and AUC in pediatric patients with type 2 diabetes (11-16 years of age, n=28, mean body weight of 97 kg) differed < 6% from historical values in healthy adults.

Gender

There is no information on the effect of gender on the pharmacokinetics of glyburide.

Metformin pharmacokinetic parameters did not differ significantly in subjects with or without type 2 diabetes when analyzed according to gender (males=19, females=16). Similarly, in controlled clinical studies in patients with type 2 diabetes, the antihyperglycemic effect of metformin was comparable in males and females.

Race

No information is available on race differences in the pharmacokinetics of glyburide.

No studies of metformin pharmacokinetic parameters according to race have been performed. In controlled clinical studies of metformin in patients with type 2 diabetes, the antihyperglycemic effect was comparable in whites (n=249), blacks (n=51), and Hispanics (n=24).

Clinical Studies

Patients with Inadequate Glycemic Control on Diet and Exercise Alone

In a 20-week, double-blind, multicenter U.S. clinical trial, a total of 806 drug-naive patients with type 2 diabetes, whose hyperglycemia was not adequately controlled with diet and exercise alone (baseline fasting plasma glucose [FPG] < 240 mg/dL, baseline hemoglobin A1c [HbA1c] between 7% and 11%), were randomized to receive initial therapy with placebo, 2.5 mg glyburide, 500 mg metformin, Tai Bi 1.25 mg/250 mg, or Tai Bi 2.5 mg/500 mg. After 4 weeks, the dose was progressively increased (up to the 8-week visit) to a maximum of 4 tablets daily as needed to reach a target FPG of 126 mg/dL. Trial data at 20 weeks are summarized in Table 2.

Table 2: Placebo- and Active-Controlled Trial of Tai Bi in Patients with Inadequate Glycemic Control on Diet and Exercis e Alone: Summary of Trial Data at 20 Weeks

Treatment with Tai Bi resulted in significantly greater reduction in HbA and postprandial plasma glucose (PPG) compared to glyburide, metformin, or placebo. Also, Tai Bi therapy resulted in greater reduction in FPG compared to glyburide, metformin, or placebo, but the differences from glyburide and metformin did not reach statistical significance.

Changes in the lipid profile associated with Tai Bi treatment were similar to those seen with glyburide, metformin, and placebo.

The double-blind, placebo-controlled trial described above restricted enrollment to patients with HbA1c < 11% or FPG < 240 mg/dL. Screened patients ineligible for the first trial because of HbA1c and/or FPG exceeding these limits were treated directly with Tai Bi 2.5 mg/500 mg in an open-label, uncontrolled protocol. In this study, 3 out of 173 patients (1.7%) discontinued because of inadequate therapeutic response. Across the group of 144 patients who completed 26 weeks of treatment, mean HbA1c was reduced from a baseline of 10.6% to 7.1%. The mean baseline FPG was 283 mg/dL and reduced to 164 and 161 mg/dL after 2 and 26 weeks, respectively. The mean final titrated dose of Tai Bi was 7.85 mg/1569 mg (equivalent to approximately 3 Tai Bi 2.5 mg/500 mg tablets per day).

Patients with Inadequate Glycemic Control on Sulfonylurea Alone

In a 16-week, double-blind, active-controlled U.S. clinical trial, a total of 639 patients with type 2 diabetes not adequately controlled (mean baseline HbA1c 9.5%, mean baseline FPG 213 mg/dL) while being treated with at least one-half the maximum dose of a sulfonylurea (eg, glyburide 10 mg, glipizide 20 mg) were randomized to receive glyburide (fixed dose, 20 mg), metformin (500 mg), Tai Bi 2.5 mg/500 mg, or Tai Bi 5 mg/500 mg. The doses of metformin and Tai Bi were titrated to a maximum of 4 tablets daily as needed to achieve FPG < 140 mg/dL. Trial data at 16 weeks are summarized in Table 3.

Table 3: Tai Bi in Patients with Inadequate Glycemic Control on Sulfonylurea Alone: Summary of Trial Data at 16 Weeks

After 16 weeks, there was no significant change in the mean HbA in patients randomized to glyburide or metformin therapy. Treatment with Tai Bi at doses up to 20 mg/2000 mg per day resulted in significant lowering of HbA , FPG, and PPG from baseline compared to glyburide or metformin alone.

Addition of Thiazolidinediones to Tai Bi Therapy

In a 24-week, double-blind, multicenter U.S. clinical trial, patients with type 2 diabetes not adequately controlled on current oral antihyperglycemic therapy (either monotherapy or combination therapy) were first switched to open label Tai Bi 2.5 mg/500 mg tablets and titrated to a maximum daily dose of 10 mg/2000 mg. A total of 365 patients inadequately controlled (HbA1c > 7.0% and ≤ 10%) after 10 to 12 weeks of a daily Tai Bi dose of at least 7.5 mg/1500 mg were randomized to receive addon therapy with rosiglitazone 4 mg or placebo once daily. After 8 weeks, the rosiglitazone dose was increased to a maximum of 8 mg daily as needed to reach a target mean daily glucose of 126 mg/dL or HbA1c < 7%. Trial data at 24 weeks or the last prior visit are summarized in Table 4.

Table 4: Effects of Adding Rosiglitazone or Placebo in Patients Treated with Tai Bi in a 24-Week Trial

For patients who did not achieve adequate glycemic control on Tai Bi, the addition of rosiglitazone, compared to placebo, resulted in significant lowering of HbA and FPG.