Avandamet (+Rosiglitazone)

Dosage Forms And Strengths

Each film-coated oval tablet contains rosiglitazone as the maleate and metformin hydrochloride as follows:

• 2 mg/500 mg - pale pink, debossed with gsk on one side and 2/500 on the other
• 4 mg/500 mg - orange, debossed with gsk on one side and 4/500 on the other
• 2 mg/1,000 mg - yellow, debossed with gsk on one side and 2/1000 on the other
• 4 mg/1,000 mg - pink, debossed with gsk on one side and 4/1000 on the other

Storage And Handling

Each film-coated oval tablet contains rosiglitazone as the maleate and metformin hydrochloride as follows:

2 mg/500 mg - pale pink, tablet, debossed with gsk on one side and 2/500 on the other.
4 mg/500 mg - orange, tablet, debossed with gsk on one side and 4/500 on the other.
2 mg/1,000 mg - yellow, tablet, debossed with gsk on one side and 2/1000 on the other.
4 mg/1,000 mg - pink, tablet, debossed with gsk on one side and 4/1000 on the other.

2 mg/500 mg bottles of 60: NDC 0173-0837-18
4 mg/500 mg bottles of 60: NDC 0173-0839-18
2 mg/1,000 mg bottles of 60: NDC 0173-0838-18
4 mg/1,000 mg bottles of 60: NDC 0173-0840-18

Store at 25°C (77°F); excursions permitted to 15° to 30°C (59° to 86°F). Dispense in a tight, light-resistant container.

GlaxoSmithKline, Research Triangle Park, NC 27709. May 2014

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

Important Limitations of Use

• Due to its mechanism of action, rosiglitazone is active only in the presence of endogenous insulin. Therefore, AVANDAMET should not be used in patients with type 1 diabetes.
• Coadministration of AVANDAMET with insulin is not recommended.

The dosage of antidiabetic therapy with AVANDAMET should be individualized on the basis of effectiveness and tolerability. The risk-benefit of initiating monotherapy versus dual therapy with AVANDAMET should be considered.

Starting Dose

AVANDAMET is generally given in divided doses with meals.

All patients should start the rosiglitazone component of AVANDAMET at the lowest recommended dose. Further increases in the dose of rosiglitazone should be accompanied by careful monitoring for adverse events related to fluid retention.

Patients Inadequately Controlled on Diet and Exercise

If therapy with a combination tablet containing rosiglitazone and metformin is considered appropriate for a patient with type 2 diabetes mellitus inadequately controlled on diet and exercise alone, the recommended starting dose of AVANDAMET is 2 mg/500 mg administered once or twice daily. For patients with HbA1c >11% or fasting plasma glucose (FPG) >270 mg/dL, a starting dose of 2 mg/500 mg twice daily may be considered. The dose of AVANDAMET may be increased in increments of 2 mg/500 mg per day given in divided doses if patients are not adequately controlled after 4 weeks. The maximum dose of AVANDAMET is 8 mg/2,000 mg per day.

Patients Inadequately Controlled on Rosiglitazone or Metformin Monotherapy

If therapy with a combination tablet containing rosiglitazone and metformin is considered appropriate for a patient with type 2 diabetes mellitus inadequately controlled on rosiglitazone or metformin monotherapy, then the selection of the dose of AVANDAMET should be based on the patient's current doses of rosiglitazone and/or metformin.

To switch to AVANDAMET for patients currently treated with metformin, the usual starting dose of AVANDAMET is 4 mg rosiglitazone (total daily dose) plus the dose of metformin already being taken (see Table 1).

To switch to AVANDAMET for patients currently treated with rosiglitazone, the usual starting dose of AVANDAMET is 1,000 mg metformin (total daily dose) plus the dose of rosiglitazone already being taken (see Table 1).

When switching from combination therapy of rosiglitazone plus metformin as separate tablets, the usual starting dose of AVANDAMET is the dose of rosiglitazone and metformin already being taken.

Table 1: AVANDAMET Starting Dose for Patients Treated With Metformin and/or Rosiglitazone

Dose Titration

AVANDAMET is generally given in divided doses with meals, with gradual dose escalation. This reduces gastrointestinal side effects (largely due to metformin) and permits determination of the minimum effective dose for the individual patient.

Sufficient time should be given to assess adequacy of therapeutic response. FPG should be used initially to determine the therapeutic response to AVANDAMET. If additional glycemic control is needed, the daily dose of AVANDAMET may be increased by increments of 4 mg rosiglitazone and/or 500 mg metformin.

After an increase in metformin dosage, dose titration is recommended if patients are not adequately controlled after 1 to 2 weeks. After an increase in rosiglitazone dosage, dose titration is recommended if patients are not adequately controlled after 8 to 12 weeks.

Maximum Dose

The maximum recommended total daily dose of AVANDAMET is 8 mg rosiglitazone (taken as 4 mg twice daily) and 2,000 mg metformin (taken as 1,000 mg twice daily).

Specific Patient Populations

Renal Impairment

Any dosage adjustment should be based on a careful assessment of renal function. Generally, elderly, debilitated, and malnourished patients should not be titrated to the maximum dose of AVANDAMET. Monitoring of renal function is necessary to aid in prevention of metformin-associated lactic acidosis, particularly in the elderly.

Hepatic Impairment

Liver enzymes should be measured prior to initiating treatment with AVANDAMET. Therapy with AVANDAMET should not be initiated if the patient exhibits clinical evidence of active liver disease or increased serum transaminase levels (ALT >2.5X upper limit of normal at start of therapy). After initiation of AVANDAMET, liver enzymes should be monitored periodically per the clinical judgment of the healthcare professional.

Geriatric

The initial and maintenance dosing of AVANDAMET should be conservative in patients with advanced age, due to the potential for decreased renal function in this population.

Pediatric

Safety and effectiveness of AVANDAMET in pediatric patients have not been established. AVANDAMET and rosiglitazone are not recommended for use in pediatric patients.

Pregnancy

AVANDAMET is not recommended for use in pregnancy.

• Initiation in patients with established New York Heart Association (NYHA) Class III or IV heart failure.
• Use in patients with renal disease or renal dysfunction [e.g., 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.
• Use in patients with acute or chronic metabolic acidosis, including diabetic ketoacidosis, with or without coma.
• Use 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. AVANDAMET should be temporarily discontinued in these patients.
• Use in patients with a history of a hypersensitivity reaction to rosiglitazone or any of the product's ingredients.

Pregnancy Category C.

All pregnancies have a background risk of birth defects, loss, or other adverse outcome regardless of drug exposure. This background risk is increased in pregnancies complicated by hyperglycemia and may be decreased with good metabolic control. It is essential for patients with diabetes or history of gestational diabetes to maintain good metabolic control before conception and throughout pregnancy. Careful monitoring of glucose control is essential in such patients. Most experts recommend that insulin monotherapy be used during pregnancy to maintain blood glucose levels as close to normal as possible. AVANDAMET should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Human Data

There are no adequate and well-controlled trials with AVANDAMET or its individual components in pregnant women. Rosiglitazone has been reported to cross the human placenta and be detectable in fetal tissue. The clinical significance of these findings is unknown.

Animal Studies

No animal studies have been conducted with AVANDAMET. The following data are based on findings in studies performed with rosiglitazone or metformin individually.

Rosiglitazone: There was no effect on implantation or the embryo with rosiglitazone treatment during early pregnancy in rats, but treatment during mid-late gestation was associated with fetal death and growth retardation in both rats and rabbits. Teratogenicity was not observed at doses up to 3 mg/kg in rats and 100 mg/kg in rabbits (approximately 20 and 75 times human AUC at the maximum recommended human daily dose of the rosiglitazone component of AVANDAMET, respectively). Rosiglitazone caused placental pathology in rats (3 mg/kg/day). Treatment of rats during gestation through lactation reduced litter size, neonatal viability, and postnatal growth, with growth retardation reversible after puberty. For effects on the placenta, embryo/fetus, and offspring, the no-effect dose was 0.2 mg/kg/day in rats and 15 mg/kg/day in rabbits. These no-effect levels are approximately 4 times human AUC at the maximum recommended human daily dose of the rosiglitazone component of AVANDAMET. Rosiglitazone reduced the number of uterine implantations and live offspring when juvenile female rats were treated at 40 mg/kg/day from 27 days of age through to sexual maturity (approximately 68 times human AUC at the maximum recommended daily dose). The no-effect level was 2 mg/kg/day (approximately 4 times human AUC at the maximum recommended daily dose). There was no effect on pre- or post-natal survival or growth.

Metformin: Metformin was not teratogenic in rats and rabbits at doses up to 600 mg/kg/day. This represents an exposure of about 2 and 6 times the maximum recommended human daily dose of 2,000 mg based on body surface area comparisons for rats and rabbits, respectively. Determination of fetal concentrations demonstrated a partial placental barrier to metformin.

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

• Lactic Acidosis
• Cardiac Failure
• Maj or Adverse Cardiovascular Events
• Edema
• Weight Gain
• Hepatic Effects
• Macular Edema
• Fractures
• Hematologic Effects
• Vitamin B₁₂ Levels
• Ovulation

Clinical Trial 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 with rates in the clinical trials of another drug and may not reflect the rates observed in practice.

Patients With Inadequate Glycemic Control on Diet and Exercise

Table 4 summarizes the incidence and types of adverse reactions without regard to causality reported in a controlled, 32-week, double-blind clinical trial of AVANDAMET in patients with inadequate glycemic control on diet and exercise (N = 468).

Table 4: Adverse Events (≥5% for AVANDAMET) Reported by Patients With Inadequate Glycemic Control on Diet and Exercise in a 32-Week, Double-blind Clinical Trial of AVANDAMET

Mild (no intervention required) to moderate (minor intervention required) symptomatic hypoglycemia was reported by 12% (18/155) of patients treated with AVANDAMET, 14/154 (9%) with metformin, and 8% (13/159) with rosiglitazone. Approximately half of these episodes were accompanied by a simultaneous capillary glucose measurement, and the rate of confirmed hypoglycemia (blood glucose ≤ 50 mg/dL) was low in this clinical trial: 0.6% (1/155) for AVANDAMET, 1.3% (2/154) for metformin, and 0% with rosiglitazone. No hypoglycemic episode led to withdrawal in patients treated with AVANDAMET, and no patients required medical intervention due to hypoglycemia.

The incidence of edema was 6% on AVANDAMET compared with 7% on rosiglitazone and 3% on metformin.

The incidence of anemia was 4% in patients treated with AVANDAMET compared with either rosiglitazone (2%) or metformin (0%).

Patients Inadequately Controlled on Rosiglitazone Monotherapy

The incidence and types of adverse events reported in controlled, 26-week clinical trials of rosiglitazone administered in combination with metformin 2,500 mg/day in comparison with adverse reactions reported in association with rosiglitazone and metformin monotherapies are shown in Table 5. Overall, the types of adverse reactions without regard to causality reported when rosiglitazone was used in combination with metformin were similar to those reported during monotherapy with rosiglitazone.

Table 5: Adverse Events (≥5% for Rosiglitazone Plus Metformin) Reported by Patients in 26-Week, Double-blind Clinical r “rials of Rosiglitazone Added to Metformin Therapy

Reports of hypoglycemia in patients treated with rosiglitazone added to maximum metformin therapy in double-blind trials were more frequent (3.0%) than in patients treated with rosiglitazone (0.6%) or metformin monotherapies (1.3%) or placebo (0.2%). Overall, anemia and edema were generally mild to moderate in severity and usually did not require discontinuation of treatment with rosiglitazone.

Edema was reported in 4.8% of patients receiving rosiglitazone compared with 1.3% on placebo, and 2.2% on metformin monotherapy and 4.4% on rosiglitazone in combination with maximum doses of metformin.

Reports of anemia (7.1%) were greater in patients treated with rosiglitazone added to metformin compared with monotherapy with rosiglitazone. Lower pre-treatment hemoglobin/hematocrit levels in patients enrolled in the metformin and rosiglitazone combination therapy clinical trials may have contributed to the higher reporting rate of anemia in these trials.

Combination With Insulin

The incidence of hypoglycemia (confirmed by fingerstick blood glucose concentration ≤ 50 mg/dL) was 14% for patients on AVANDAMET plus insulin compared with 10% for patients on insulin monotherapy.

The incidence of edema was 7% when insulin was added to AVANDAMET compared with 3% with insulin monotherapy. This trial excluded patients with pre-existing heart failure or new or worsening edema on AVANDAMET. However, in 26-week, double-blind, fixed-dose trials of rosiglitazone added to insulin, edema was reported with higher frequency (rosiglitazone in combination with insulin, 14.7%; insulin, 5.4%).

In trials in which rosiglitazone was added to insulin, rosiglitazone increased the risk of congestive heart failure.

In a trial in which insulin was added to AVANDAMET, no myocardial ischemia was observed in the insulin group (N = 158), and no congestive heart failure was reported in either group. There was one myocardial ischemic event and one sudden death in the group receiving AVANDAMET plus insulin (N = 161).

The incidence of anemia was 2% for AVANDAMET in combination with insulin compared with 1% for insulin monotherapy.

Long-term Trial of Rosiglitazone as Monotherapy

A long-term, 4- to 6-year trial (ADOPT) compared the use of rosiglitazone (n = 1,456), glyburide (n = 1,441), and metformin (n = 1,454) as monotherapy in patients recently diagnosed with type 2 diabetes who were not previously treated with antidiabetic medication. Table 6 presents adverse reactions without regard to causality; rates are expressed per 100 patient-years (PY) exposure to account for the differences in exposure to trial medication across the 3 treatment groups.

In ADOPT, fractures were reported in a greater number of women treated with rosiglitazone (9.3%, 2.7/100 patient-years) compared with glyburide (3.5%, 1.3/100 patientyears) or metformin (5.1%, 1.5/100 patient-years). The majority of the fractures in the women who received rosiglitazone were reported in the upper arm, hand, and foot. The observed incidence of fractures for male patients was similar among the 3 treatment groups.

Table 6: On-therapy Adverse Events [≥5 Events/100 Patient-years (PY)] in any Treatment Group Reported in a 4- to 6-Year Clinical Trial of B osiglitazone as Monotherapy (ADOPT)

Long-term Trial of Rosiglitazone as Combination Therapy (RECORD)

RECORD (Rosiglitazone Evaluated for Cardiac Outcomes and Regulation of Glycemia in Diabetes) was a multicenter, randomized, open-label, non-inferiority trial in subjects with type 2 diabetes inadequately controlled on maximum doses of metformin or sulfonylurea (glyburide, gliclazide, or glimepiride) to compare the time to reach the combined cardiovascular endpoint of cardiovascular death or cardiovascular hospitalization between patients randomized to the addition of rosiglitazone versus metformin or sulfonylurea. The trial included patients who have failed metformin or sulfonylurea monotherapy; those who failed metformin (n = 2,222) were randomized to receive either add-on rosiglitazone (n = 1,117) or add-on sulfonylurea (n = 1,105), and those who failed sulfonylurea (n = 2,225) were randomized to receive either add-on rosiglitazone (n = 1,103) or add-on metformin (n = 1,122). Patients were treated to target HbA1c ≤ 7% throughout the trial.

The mean age of patients in this trial was 58 years, 52% were male, and the mean duration of follow-up was 5.5 years. Rosiglitazone demonstrated non-inferiority to active control for the primary endpoint of cardiovascular hospitalization or cardiovascular death (HR 0.99, 95% CI: 0.85-1.16). There were no significant differences between groups for secondary endpoints with the exception of congestive heart failure (see Table 7). The incidence of congestive heart failure was significantly greater among patients randomized to rosiglitazone.

Table 7:Cardiovascular (CV) Outcomes for the RECORD Trial

There was an increased incidence of bone fracture for subjects randomized to rosiglitazone in addition to metformin or sulfonylurea compared with those randomized to metformin plus sulfonylurea (8.3% versus 5.3%). The majority of fractures were reported in the upper limbs and distal lower limbs. The risk of fracture appeared to be higher in females relative to control (11.5% versus 6.3%), than in males relative to control (5.3% versus 4.3%). Additional data are necessary to determine whether there is an increased risk of fracture in males after a longer period of follow-up.

Laboratory Abnormalities

Hematologic

Decreases in mean hemoglobin and hematocrit occurred in a dose-related fashion in adult patients treated with rosiglitazone (mean decreases in individual trials as much as 1.0 gram/dL hemoglobin and as much as 3.3% hematocrit). The changes occurred primarily during the first 3 months following initiation of rosiglitazone therapy or following an increase in rosiglitazone dose. The time course and magnitude of decreases were similar in patients treated with a combination of rosiglitazone and other hypoglycemic agents or monotherapy with rosiglitazone. Pre-treatment levels of hemoglobin and hematocrit were lower in patients in  metformin combination trials and may have contributed to the higher reporting rate of anemia. In a single trial in pediatric patients, decreases in hemoglobin and hematocrit (mean decreases of 0.29 g/dL and 0.95%, respectively) were reported with rosiglitazone. White blood cell counts also decreased slightly in adult patients treated with rosiglitazone. Decreases in hematologic parameters may be related to increased plasma volume observed with rosiglitazone treatment.

In controlled clinical trials of metformin 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. Such a 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 B₁₂ supplementation.

Lipids

Changes in serum lipids have been observed following treatment with rosiglitazone in adults.

Serum Transaminase Levels

In pre-approval clinical trials in 4,598 patients treated with rosiglitazone encompassing approximately 3,600 patient-years of exposure, and in a longterm 4- to 6-year trial in 1,456 patients treated with rosiglitazone (4,954 patient-years exposure), there was no evidence of drug-induced hepatotoxicity.

In pre-approval controlled trials, 0.2% of patients treated with rosiglitazone had reversible elevations in ALT >3X the upper limit of normal compared with 0.2% on placebo and 0.5% on active comparators. The ALT elevations in patients treated with rosiglitazone were reversible. Hyperbilirubinemia was found in 0.3% of patients treated with rosiglitazone compared with 0.9% treated with placebo and 1% in patients treated with active comparators. In pre-approval clinical trials, there were no cases of idiosyncratic drug reactions leading to hepatic failure.

In the 4- to 6-year ADOPT trial, patients treated with rosiglitazone (4,954 patient-years exposure), glyburide (4,244 patient-years exposure), or metformin (4,906 patient-years exposure) as monotherapy, had the same rate of ALT increase to >3X upper limit of normal (0.3 per 100 patient-years exposure).

In the RECORD trial, patients randomized to rosiglitazone in addition to metformin or sulfonylurea (10,849 patient-years exposure) and to metformin plus sulfonylurea (10,209 patientyears exposure) had a rate of ALT increase to >3X upper limit of normal of approximately 0.2 and 0.3 per 100 patient-years exposure, respectively.

Postmarketing Experience

In addition to adverse reactions reported from clinical trials, the events described below have been identified during post-approval use of AVANDAMET or its individual components. Because these events are reported voluntarily from a population of unknown size, it is not possible to reliably estimate their frequency or to always establish a causal relationship to drug exposure.

In patients receiving thiazolidinedione therapy, serious adverse events with or without a fatal outcome, potentially related to volume expansion (e.g., congestive heart failure, pulmonary edema, and pleural effusions) have been reported.

There are postmarketing reports with rosiglitazone of hepatitis, hepatic enzyme elevations to 3 or more times the upper limit of normal, and hepatic failure with and without fatal outcome, although causality has not been established. There are postmarketing reports with rosiglitazone of rash, pruritus, urticaria, angioedema, anaphylactic reaction, Stevens-Johnson syndrome , and new onset or worsening diabetic macular edema with decreased visual acuity. (See also GLUCOPHAGE® prescribing information.)

Rosiglitazone: Limited data are available with regard to overdosage in humans. In clinical trials in volunteers, rosiglitazone has been administered at single oral doses of up to 20 mg and was well tolerated. In the event of an overdose, appropriate supportive treatment should be initiated as dictated by the patient's clinical status.

Metformin: Hypoglycemia has not been seen with ingestion of up to 85 grams of metformin, although lactic acidosis has occurred in such circumstances. 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 metformin from patients in whom metformin overdosage is suspected.

In all 26-week controlled trials, across the recommended dose range, rosiglitazone as monotherapy was associated with increases in total cholesterol, LDL-cholesterol and HDLcholesterol and decreases in free fatty acids.

The lipid profiles of AVANDAMET as well as rosiglitazone and metformin monotherapies in patients who have inadequate glycemic control on diet and exercise are shown in Table 8.

Table 8: Summary of Mean^a Lipid Changes in a 32-Week Trial of AVANDAMET in Patients With Type 2 Diabetes Mellitus who Have Inadequate Glycemic Control on Diet and Exercise

The pattern of LDL, HDL, and total cholesterol changes following therapy with rosiglitazone added to metformin was generally similar to those seen with rosiglitazone monotherapy, and a small decrease in mean triglycerides was observed with the combination therapy.

Absorption

 AVANDAMET: In a bioequivalence and dose-proportionality trial of AVANDAMET 4 mg/500 mg, both the rosiglitazone component and the metformin component were bioequivalent to coadministered 4-mg rosiglitazone tablet and 500-mg metformin tablet under fasted conditions (see Table 9). In this trial, dose proportionality of rosiglitazone in the combination formulations of 1 mg/500 mg and 4 mg/500 mg was demonstrated.

Table 9: Mean (SD) Pharmacokinetic Parameters for Rosiglitazone and Metformin

Administration of AVANDAMET 4 mg/500 mg with food resulted in no change in overall exposure (AUC) for either rosiglitazone or metformin. However, there were decreases in Cmax of both components (22% for rosiglitazone and 15% for metformin, respectively) and a delay in Tmax of both components (1.5 hours for rosiglitazone and 0.5 hours for metformin, respectively). These changes are not likely to be clinically significant. The pharmacokinetics of both the rosiglitazone component and the metformin component of AVANDAMET when taken with food were similar to the pharmacokinetics of rosiglitazone and metformin when administered concomitantly as separate tablets with food.

Absorption

Rosiglitazone: The absolute bioavailability of rosiglitazone is 99%. Peak plasma concentrations are observed about 1 hour after dosing. Maximum plasma concentration (Cmax) and the area under the curve (AUC) of rosiglitazone increase in a dose-proportional manner over the therapeutic dose range.

Metformin: The absolute bioavailability of a 500-mg metformin tablet given under fasting conditions is approximately 50% to 60%. Trials using single oral doses of metformin 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.

Distribution

Rosiglitazone: The mean (CV%) oral volume of distribution (Vss/F) of rosiglitazone is approximately 17.6 (30%) liters, based on a population pharmacokinetic analysis. Rosiglitazone is approximately 99.8% bound to plasma proteins, primarily albumin.

Metformin: The apparent volume of distribution (V/F) of metformin following single oral doses of 850 mg metformin 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 mcg/mL. During controlled clinical trials, maximum metformin plasma levels did not exceed 5 mcg/mL, even at maximum doses.

Metabolism and Excretion

Rosiglitazone: Rosiglitazone is extensively metabolized with no unchanged drug excreted in the urine. The major routes of metabolism were N-demethylation and hydroxylation, followed by conjugation with sulfate and glucuronic acid. All the circulating metabolites are considerably less potent than parent and, therefore, are not expected to contribute to the insulin-sensitizing activity of rosiglitazone. In vitro data demonstrate that rosiglitazone is predominantly metabolized by Cytochrome P450 (CYP) isoenzyme 2C8, with CYP2C9 contributing as a minor pathway. Following oral or intravenous administration of [¹⁴C]rosiglitazone maleate, approximately 64% and 23% of the dose was eliminated in the urine and in the feces, respectively. The plasma half-life of [¹⁴C]related material ranged from 103 to 158 hours. The elimination half-life is 3 to 4 hours and is independent of dose.

Metabolism and Excretion

Metformin: Intravenous single-dose trials 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 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.