Repaglinide And Metformin Hydrochloride

Repaglinide And Metformin Hydrochloride is indicated as an adjunct to diet and exercise to improve glycemic control in adults with type 2 diabetes mellitus who are already treated with a meglitinide and metformin HCl or who have inadequate glycemic control on a meglitinide alone or metformin HCl alone.

Important Limitations of Use

Repaglinide And Metformin Hydrochloride should not be used in patients with type 1 diabetes or for the treatment of diabetic ketoacidosis, as it would not be effective in these settings.

Recommended Dosing

The dosage of Repaglinide And Metformin Hydrochloride should be individualized on the basis of the patient's current regimen, effectiveness and tolerability. Repaglinide And Metformin Hydrochloride can be administered 2 to 3 times a day up to a maximum daily dose of 10 mg repaglinide/2500 mg metformin HCl. No more than 4 mg repaglinide/1000 mg metformin HCl should be taken per meal. Initiation and maintenance of combination therapy with Repaglinide And Metformin Hydrochloride should be individualized to the patient, and at the discretion of the health care provider. Blood glucose monitoring should be performed to determine the therapeutic response to Repaglinide And Metformin Hydrochloride.

Repaglinide And Metformin Hydrochloride doses should usually be taken within 15 minutes prior to the meal but the timing can vary from immediately preceding the meal up to 30 minutes before the meal. Patients who skip a meal should be instructed to skip the Repaglinide And Metformin Hydrochloride dose for that meal.

Patients Inadequately Controlled with Metformin HCl Monotherapy

If therapy with a combination tablet containing repaglinide and metformin HCl is considered appropriate for a patient with type 2 diabetes mellitus inadequately controlled with metformin HCl alone, the recommended starting dose of Repaglinide And Metformin Hydrochloride is 1 mg repaglinide/500 mg metformin HCl administered twice daily with meals, with gradual dose escalation (based on glycemic response) to reduce the risk of hypoglycemia with repaglinide.

Patients Inadequately Controlled with Meglitinide Monotherapy

If therapy with a combination tablet containing repaglinide and metformin HCl is considered appropriate for a patient with type 2 diabetes mellitus inadequately controlled with repaglinide alone, the recommended starting dose of the metformin HCl component of Repaglinide And Metformin Hydrochloride should be 500 mg metformin HCl twice a day, with gradual dose escalation (based on glycemic response) to reduce gastrointestinal side effects associated with metformin HCl.

Patients Currently Using Repaglinide and Metformin HCl Concomitantly

For patients switching from repaglinide co-administered with metformin HCl, Repaglinide And Metformin Hydrochloride can be initiated at the dose of repaglinide and metformin HCl similar to (but not exceeding) the patient's current doses, then may be titrated to the maximum daily dose as necessary to achieve targeted glycemic control.

No studies have been performed examining the safety and efficacy of Repaglinide And Metformin Hydrochloride in patients previously treated with other oral antihyperglycemic agents and switched to Repaglinide And Metformin Hydrochloride. Any change in therapy should be undertaken with care and with appropriate monitoring as changes in glycemic control can occur.

Repaglinide And Metformin Hydrochloride is contraindicated in:

• Renal impairment (e.g., serum creatinine levels ≥1.5 mg/dL [males], ≥1.4 mg/dL [females], or abnormal creatinine clearance).
• Acute or chronic metabolic acidosis, including diabetic ketoacidosis. Diabetic ketoacidosis should be treated with insulin.
• Patients receiving gemfibrozil.
• Patients with known hypersensitivity to repaglinide, metformin HCl or any inactive ingredients in Repaglinide And Metformin Hydrochloride.

WARNINGS

Included as part of the PRECAUTIONS section.

PRECAUTIONS

Lactic Acidosis

Metformin hydrochloride

Lactic acidosis is a rare, but serious, metabolic complication that can occur due to metformin accumulation during treatment with Repaglinide And Metformin Hydrochloride; 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 HCl is very low (approximately 0.03 cases/1,000 patient-years of exposure, with approximately 0.015 fatal cases/1,000 patient-years of exposure). In more than 20,000 patient-years exposure to metformin HCl in clinical trials, there were no reports of lactic acidosis. Reported cases have occurred primarily in diabetic patients with significant renal impairment, 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 impairment and the patient's age. The risk of lactic acidosis may, therefore, be significantly decreased by regular monitoring of renal function in patients taking Repaglinide And Metformin Hydrochloride and by use of the minimum effective dose of Repaglinide And Metformin Hydrochloride. In particular, treatment of the elderly should be accompanied by careful monitoring of renal function. Treatment with Repaglinide And Metformin Hydrochloride 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, Repaglinide And Metformin Hydrochloride 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, Repaglinide And Metformin Hydrochloride 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 Repaglinide And Metformin Hydrochloride, since alcohol potentiates the effects of metformin HCl on lactate metabolism. In addition, Repaglinide And Metformin Hydrochloride should be temporarily discontinued prior to any intravascular radiocontrast study and for any surgical procedure.

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. Repaglinide And Metformin Hydrochloride 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 dose level of Repaglinide And Metformin Hydrochloride, gastrointestinal symptoms, which are common during initiation of therapy, 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 Repaglinide And Metformin Hydrochloride 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 sample handling.

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 Repaglinide And Metformin Hydrochloride, the drug should be discontinued immediately and general supportive measures promptly instituted. Because metformin HCl 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.

Impaired Renal Function

Patients with renal impairment should not receive Repaglinide And Metformin Hydrochloride.

As metformin is substantially excreted by the kidney, before initiation of therapy with Repaglinide And Metformin Hydrochloride and at least  annually thereafter, renal function should be assessed and verified as normal. In patients in whom development of  renal impairment is anticipated, renal function should be assessed more frequently and Repaglinide And Metformin Hydrochloride discontinued if  evidence of renal impairment is present.

Radiologic Studies with Intravascular Iodinated 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 HCl. Therefore, in patients in whom any such study is planned, Repaglinide And Metformin Hydrochloride 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 re-evaluated and found to be normal.

Impaired Hepatic Function

Hepatic impairment has been associated with some cases of lactic acidosis. Therefore, Repaglinide And Metformin Hydrochloride should generally be avoided in patients with hepatic impairment.

Alcohol Intake

Alcohol potentiates the effect of metformin on lactate metabolism. Patients should be warned against excessive alcohol intake while receiving Repaglinide And Metformin Hydrochloride.

Combination with NPH-insulin

Repaglinide

Repaglinide is not indicated for use in combination with NPH-insulin.

Across seven controlled clinical trials, there were six serious adverse events (1.4%) of myocardial ischemia with repaglinide in combination with NPH-insulin compared to one event (0.3%) in patients using insulin alone.

Drug Interactions

Repaglinide is partly metabolized by CYP2C8 and CYP3A4 and appears to be a substrate for active hepatic uptake transporter (organic anion transporting protein OATP1B1). Drugs that inhibit CYP2C8, CYP3A4, or OATP1B1 (e.g., cyclosporine) may increase plasma concentrations of repaglinide. Dose reduction of repaglinide may be needed.

Gemfibrozil significantly increased repaglinide exposure. Therefore, patients should not take Repaglinide And Metformin Hydrochloride with gemfibrozil.

Hypoglycemia

Most blood glucose-lowering drugs, including repaglinide, can cause hypoglycemia. Patients who have not previously been treated with a meglitinide should be started on the lowest available repaglinide component of Repaglinide And Metformin Hydrochloride to reduce the risk of hypoglycemia. Elderly, debilitated or malnourished patients and those with adrenal or pituitary insufficiency or alcohol intoxication are particularly susceptible to hypoglycemia. Hypoglycemia may be difficult to recognize in the elderly and in people who are taking β-adrenergic blocking drugs.

Vitamin B12 Levels

In controlled clinical trials of metformin HCl of 29 weeks' duration, a decrease to subnormal levels of previously normal serum vitamin B12 levels, without clinical manifestations, was observed in approximately 7% of patients. This finding, possibly due to interference with B12 absorption from the B12-intrinsic factor complex, is rarely associated with anemia and appears to be rapidly reversible with discontinuation of metformin HCl or vitamin B12 supplementation. Measurement of hematologic parameters on an annual basis is advised in patients on Repaglinide And Metformin Hydrochloride and any apparent abnormalities should be appropriately investigated and managed.

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.

Surgical Procedures

Use of Repaglinide And Metformin Hydrochloride 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.

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 temporary loss of glycemic control may occur. At such times, it may be necessary to withhold Repaglinide And Metformin Hydrochloride and temporarily administer insulin. Repaglinide And Metformin Hydrochloride may be reinstituted after the acute episode is resolved.

Use of Concomitant Medications Affecting 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 should be used with caution.

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 receiving Repaglinide And Metformin Hydrochloride, the drug should be promptly discontinued.

Change in Clinical Status of Patients with Previously Controlled Type 2 Diabetes

A patient with type 2 diabetes previously well-controlled on Repaglinide And Metformin Hydrochloride 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, Repaglinide And Metformin Hydrochloride must be stopped immediately and other appropriate corrective measures initiated.

Macrovascular Outcomes

There have been no clinical studies establishing conclusive evidence of macrovascular risk reduction with Repaglinide And Metformin Hydrochloride or any other oral anti-diabetic drug.

Nonclinical Toxicology

Carcinogenesis, Mutagenesis, Impairment of Fertility

Repaglinide And Metformin Hydrochloride

No animal studies have been conducted with the combined products in Repaglinide And Metformin Hydrochloride to evaluate carcinogenesis, mutagenesis and impairment of fertility. The following data are based on findings in studies performed with the individual components.

Repaglinide

In a 104-week carcinogenicity study in rats at doses up to 120 mg/kg/day, the incidences of benign adenomas of the thyroid and liver were increased in male rats. The higher incidences of thyroid and liver tumors in male rats were not seen at lower dose of 30 mg/kg/day and 60 mg/kg/day respectively (which are over 15 and 30 times, respectively, clinical exposures on a mg/m² basis).

In a 104-week carcinogenicity study in mice at doses up to 500 mg/kg/day, no evidence of carcinogenicity was found in mice (which is approximately 125 times clinical exposure on a mg/m² basis).

Repaglinide was non-genotoxic in a battery of in vivo and in vitro studies: Bacterial mutagenesis (Ames test), in vitro forward cell mutation assay in V79 cells (HGPRT), in vitro chromosomal aberration assay in human lymphocytes, unscheduled and replicating DNA synthesis in rat liver, and in vivo mouse and rat micronucleus tests.

In a rat fertility study, repaglinide was administered to male and female rats at doses up to 300 and 80 mg/kg/day, respectively. No adverse effects on fertility were observed (which are over 40 times clinical exposure on a mg/m² basis).

Metformin HCl

In a 104-week carcinogenicity study in rats at doses up to 900 mg/kg/day, the incidences of benign stromal uterine polyps were increased in female rats at 900 mg/kg/day (which is approximately four times the maximal recommended human daily dose of 2000 mg of metformin HCl component of Repaglinide And Metformin Hydrochloride on a mg/m² basis).

In a 91-week carcinogenicity study in mice at doses up to 1500 mg/kg/day, no evidence of carcinogenicity was found in mice (which is approximately four times the maximal recommended human daily dose of 2000 mg of metformin HCl component of Repaglinide And Metformin Hydrochloride on a mg/m² basis).

There was no evidence of a mutagenic potential of metformin HCl 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.

In a rat fertility study, metformin HCl was administered to male and female rats at doses up to 600 mg/kg/day. No adverse effects on fertility were observed (which is approximately three times the maximal recommended human daily dose of 2000 mg of metformin HCl component of Repaglinide And Metformin Hydrochloride on a mg/m² basis).

Use In Specific Populations

Pregnancy

Pregnancy Category C

There are no adequate and well-controlled studies in pregnant women with Repaglinide And Metformin Hydrochloride or its individual components. Because animal reproduction studies are not always predictive of human response, Repaglinide And Metformin Hydrochloride like other antidiabetic medications, should be used during pregnancy only if clearly needed.

No animal studies have been conducted with the combined products in Repaglinide And Metformin Hydrochloride. The following data are based on findings in studies performed with repaglinide or metformin individually.

Repaglinide

Repaglinide was not teratogenic in rats at doses 40 times, and rabbits approximately 0.8 times the clinical exposure (on a mg/m² basis) throughout pregnancy. Offspring of rat dams exposed to repaglinide at 15 times clinical exposure on a mg/m² basis during days 17 to 22 of gestation and during lactation developed nonteratogenic skeletal deformities consisting of shortening, thickening, and bending of the humerus during the postnatal period. This effect was not seen at doses up to 2.5 times clinical exposure (on a mg/m² basis) on days 1 to 22 of pregnancy or at higher doses given during days 1 to 16 of pregnancy. Relevant human exposure has not occurred to date and therefore the safety of repaglinide administration throughout pregnancy or lactation cannot be established.

Metformin HCl

Metformin HCl alone was not teratogenic in rats or rabbits at doses up to 600 mg/kg/day. This represents an exposure of approximately two and six times the near-maximal efficacious human daily dose of 2000 mg of the metformin HCl component of Repaglinide And Metformin Hydrochloride based on body surface area comparisons for rats and rabbits, respectively. Determination of fetal concentrations demonstrated a partial placental barrier to metformin.

Nursing Mothers

No studies in lactating animals have been conducted with the Repaglinide And Metformin Hydrochloride fixed dose combination. In studies performed with individual components, both repaglinide and metformin are excreted into milk of lactating rats.

Repaglinide

In rat reproduction studies, measurable levels of repaglinide were detected in the breast milk of the dams and lowered blood glucose levels were observed in the pups. Cross fostering studies indicated that skeletal changes could be induced in control pups nursed by treated dams, although this occurred to a lesser degree than those pups treated in utero.

Metformin HCl

Studies in lactating rats with metformin HCl show that it is excreted into milk and reaches levels comparable to  those in plasma. It is not known whether repaglinide or metformin are excreted in human milk. Repaglinide And Metformin Hydrochloride is not recommended in nursing mothers because it may potentially cause hypoglycemia in nursing infants.

Pediatric Use

Safety and effectiveness of Repaglinide And Metformin Hydrochloride in pediatric patients have not been established. Repaglinide And Metformin Hydrochloride is not recommended for use in children.

Geriatric Use

Healthy volunteers treated with repaglinide 2 mg before each of 3 meals, showed no significant differences in  repaglinide pharmacokinetics between the group of patients <65 years of age and those ≥65 years of age. In patients with advanced age, Repaglinide And Metformin Hydrochloride 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, dose adjustment of Repaglinide And Metformin Hydrochloride should be based on a careful assessment of renal function.

Most Frequently Observed Adverse Reactions

Repaglinide

In clinical trials of repaglinide, hypoglycemia is the most common adverse reaction (> 5%) leading to withdrawal of patients treated with repaglinide.

Metformin HCl

Gastrointestinal reactions (e.g., diarrhea, nausea, vomiting) are the most common adverse reactions (> 5%) with metformin HCl treatment and are more frequent at higher metformin HCl doses.

Clinical Trial Experience

Because clinical trials are conducted under 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.

Patients with Inadequate Glycemic Control on Metformin HCl Monotherapy

Table 1 summarizes the most common adverse reactions occurring in a 6-month randomized study of repaglinide added to metformin HCl in patients with type 2 diabetes inadequately controlled on metformin HCl alone.

Table 1: Repaglinide added to metformin HCl in patients with type 2 diabetes inadequately controlled on metformin HCl alone. Adverse reaction reported (regardless of Investigator Assessment of Causality) in ≥10% of patients receiving combination therapy*

Cardiovascular Events in repaglinide monotherapy trials

In one-year trials comparing repaglinide to sulfonylurea drugs, the incidence of angina was 1.8% for both treatments, with an incidence of chest pain of 1.8% for repaglinide and 1.0% for sulfonylureas. The incidence of other selected cardiovascular events (hypertension, abnormal electrocardiogram, myocardial infarction, arrhythmias, and palpitations) was ≤ 1% and not different between repaglinide and the comparator drugs.

The incidence of total serious cardiovascular adverse events, including ischemia, was higher for repaglinide (51/1228 or 4%) than for sulfonylurea drugs (13/498 or 3%) in controlled clinical trials. In 1-year controlled trials, repaglinide treatment was not associated with excess mortality when compared to the rates observed with other oral hypoglycemic agent therapies such as glyburide and glipizide.

Seven controlled clinical trials included repaglinide combination therapy with NPH-insulin (n=431), insulin formulations alone (n=388) or other combinations (sulfonylurea plus NPH-insulin or repaglinide plus metformin HCl) (n=120). There were six serious adverse events of myocardial ischemia in patients treated with repaglinide plus NPH-insulin (1.4%) from two studies, and one event in patients using insulin formulations alone from another study (0.3%).

Postmarketing Experience

Repaglinide

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

Postmarketing experience with repaglinide includes infrequent reports of the following adverse events; alopecia, hemolytic anemia, pancreatitis, Stevens-Johnson Syndrome, and severe hepatic dysfunction including jaundice and hepatitis.

Repaglinide And Metformin Hydrochloride

No data are available with regard to overdose of Repaglinide And Metformin Hydrochloride. Findings related to the individual active substances are listed below.

Repaglinide

In a clinical trial, dizziness, headache, and diarrhea were reported in subjects receiving increasing doses of repaglinide up to 80 mg a day for 14 days. Hypoglycemia did not occur when meals were given with these high doses.

Hypoglycemic symptoms without loss of consciousness or neurologic 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. Patients should be closely monitored for a minimum of 24 to 48 hours, since hypoglycemia may recur after apparent clinical recovery. There is no evidence that repaglinide is dialyzable using hemodialysis. 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 more dilute (10%) glucose solution at a rate that will maintain the blood glucose at a level above 100 mg/dL.

Metformin HCl

Overdose of metformin HCl has occurred, including ingestion of amounts greater than 50 grams. Hypoglycemia was reported in approximately 10% of cases, but no causal association with metformin HCl has been established. Lactic acidosis has been reported in approximately 32% of metformin HCl overdose cases. 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 HCl overdosage is suspected.

Repaglinide And Metformin Hydrochloride

The results of a bioequivalence study in healthy subjects (Table 2) demonstrated that Repaglinide And Metformin Hydrochloride (repaglinide/metformin HCl) 1 mg/500 mg and 2 mg/500 mg combination tablets are bioequivalent to coadministration of corresponding doses of repaglinide and metformin HCl as individual tablets. Repaglinide dose proportionality was demonstrated for Repaglinide And Metformin Hydrochloride (2 mg/500 mg) and Repaglinide And Metformin Hydrochloride (1 mg/500 mg).

Table 2: Mean (SD) Pharmacokinetic Parameters for Repaglinide and Metformin

Absorption and Bioavailability

Repaglinide: After single and multiple oral doses in healthy subjects or in patients with type 2 diabetes, peak plasma drug levels (Cmax) occur within 1 hour (Tmax). Repaglinide is eliminated from the blood stream with a half-life of approximately 1 hour. The mean absolute bioavailability is 56%. When repaglinide was given with food, the mean Tmax was not changed, but the mean Cmax and AUC (area under the time/plasma concentration curve) were decreased 20% and 12.4%, respectively.

Metformin HCl: The absolute bioavailability of a 500 mg metformin HCl tablet given under fasting conditions is approximately 50% to 60%. Studies using single oral doses of metformin HCl tablets of 500 mg to 1,500 mg, and 850 mg to 2,550 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 (Cmax), a 25% lower area under plasma concentration (AUC) and a 35-minute prolongation of time to peak plasma concentration (Tmax) following administration of a single 850 mg tablet of metformin HCl with food, compared to the same tablet strength administered fasting. The clinical relevance of these decreases is unknown.

Distribution

Repaglinide: After intravenous (IV) dosing in healthy subjects, the volume of distribution at steady state (Vss) was 31 L, and the total body clearance (CL) was 38 L/h. Protein binding and binding to human serum albumin was greater than 98%.

Metformin HCl: The apparent volume of distribution (V/F) of metformin following single oral dose 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 HCl, steady state plasma concentrations of metformin are reached within 24-48 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

Repaglinide: Repaglinide is completely metabolized by oxidative biotransformation and direct conjugation with glucuronic acid after either an intravenous or oral dose. The major metabolites are an oxidized dicarboxylic acid (M2), the aromatic amine (M1), and the acyl glucuronide (M7). The cytochrome P-450 enzyme system, specifically 2C8 and 3A4, have been shown to be involved in the N-dealkylation of repaglinide to M2 and the further oxidation to M1. Metabolites do not contribute to the glucose-lowering effect of repaglinide. Within 96 hours after dosing with ¹⁴C-repaglinide as a single, oral dose, approximately 90% of the radiolabel was recovered in the feces and approximately 8% in the urine. Only 0.1% of the dose is cleared in the urine as parent compound. The major metabolite (M2) accounted for 60% of the administered dose. Less than 2% of parent drug was recovered in feces. Repaglinide appears to be a substrate for active hepatic uptake transporter (organic anion transporting protein OATP1B1).

Metformin HCl: 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) or biliary excretion. Renal clearance 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.