Mechanism of Action

DUETACT

DUETACT combines two antihyperglycemic agents with different mechanisms of action to improve glycemic control in patients with type 2 diabetes: pioglitazone hydrochloride, a member of the thiazolidinedione class, and glimepiride, a member of the sulfonylurea class. Thiazolidinediones are insulin-sensitizing agents that act primarily by enhancing peripheral glucose utilization, whereas sulfonylureas are insulin secretogogues that act primarily by stimulating release of insulin from functioning pancreatic beta cells.

Pioglitazone hydrochloride

Pioglitazone depends on the presence of insulin for its mechanism of action. Pioglitazone decreases insulin resistance in the periphery and in the liver resulting in increased insulin-dependent glucose disposal and decreased hepatic glucose output. Pioglitazone is a potent and highly selective agonist for peroxisome proliferator-activated receptor-gamma (PPARγ). PPAR receptors are found in tissues important for insulin action such as adipose tissue, skeletal muscle, and liver. Activation of PPARγ nuclear receptors modulates the transcription of a number of insulin responsive genes involved in the control of glucose and lipid metabolism.

In animal models of diabetes, pioglitazone reduces the hyperglycemia, hyperinsulinemia, and hypertriglyceridemia characteristic of insulin-resistant states such as type 2 diabetes. The metabolic changes produced by pioglitazone result in increased responsiveness of insulin-dependent tissues and are observed in numerous animal models of insulin resistance.

Since pioglitazone enhances the effects of circulating insulin (by decreasing insulin resistance), it does not lower blood glucose in animal models that lack endogenous insulin.

Glimepiride

The primary mechanism of action of glimepiride in lowering blood glucose appears to be dependent on stimulating the release of insulin from functioning pancreatic beta cells. In addition, extrapancreatic effects may also play a role in the activity of sulfonylureas such as glimepiride. This is supported by both preclinical and clinical studies demonstrating that glimepiride administration can lead to increased sensitivity of peripheral tissues to insulin. These findings are consistent with the results of a long-term, randomized, placebo-controlled trial in which glimepiride therapy improved postprandial insulin/C-peptide responses and overall glycemic control without producing clinically meaningful increases in fasting insulin/C-peptide levels. However, as with other sulfonylureas, the mechanism by which glimepiride lowers blood glucose during long-term administration has not been clearly established.

Pharmacokinetics and Drug Metabolism

Absorption and Bioavailability

DUETACT

Bioequivalence studies were conducted following a single dose of the DUETACT 30 mg/2 mg and 30 mg/4 mg tablets and concomitant administration of ACTOS (30 mg) and glimepiride (2 mg or 4 mg) under fasting conditions in healthy subjects.

Based on the area under the curve (AUC) and maximum concentration (Cmax) of both pioglitazone and glimepiride, DUETACT 30 mg/2 mg and 30 mg/4 mg were bioequivalent to ACTOS 30 mg concomitantly administered with glimepiride (2 mg or 4 mg, respectively) (Table 1).

Table 1: Mean (SD) Pharmacokinetic Parameters for DUETACT

Regimen		N	AUC(0-inf) (ng• h/mL)	N	Cmax (ng/mL)	N	Tmax (h)	N	T½ (h)
30 mg/2 mg DUETACT	pioglitazone	58	11414 (2704)	66	910 (336)	66	1.81 (1.11)	65	14.02 (6.23)
	glimepiride	62	651 (239)	66	156 (52.5)	66	1.39 (0.29)	63	7.05 (4.32)
30 mg pioglitazone + 2 mg	pioglitazone	58	11496 (2926)	66	975 (367)	66	1.48 (1.13)	65	12.71 (5.60)
glimepiride tablets	glimepiride	62	635 (240)	66	165 (53.1)	66	1.36 (0.35)	63	5.54 (4.21)
30 mg/4 mg DUETACT	pioglitazone	55	11119 (3399)	67	1062 (333)	67	1.53 (0.81)	67	10.88 (4.71)
	glimepiride	64	1645 (576)	67	319 (95.3)	67	1.45 (0.39)	64	10.52 (3.49)
30 mg pioglitazone + 4 mg	pioglitazone	55	10674 (2895)	67	1026 (346)	67	1.52 (1.95)	67	12.21 (6.30)
glimepiride tablets	glimepiride	64	1590 (554)	67	313 (97.8)	67	1.76 (1.13)	64	9.07 (3.47)

Food did not change the systemic exposures of glimepiride or pioglitazone following administration of DUETACT. The presence of food did not significantly alter the time to peak serum concentration of glimepiride or pioglitazone or peak exposure (Cmax) of pioglitazone. However, for glimepiride, there was a 22% increase in Cmax when DUETACT was administered with food.

Pioglitazone hydrochloride

Following oral administration, in the fasting state, pioglitazone is first measurable in serum within 30 minutes, with peak concentrations observed within 2 hours.

Glimepiride

After oral administration, glimepiride is completely (100%) absorbed from the GI tract. Studies with single oral doses in normal subjects and with multiple oral doses in patients with type 2 diabetes have shown significant absorption of glimepiride within 1 hour after administration and Cmax at 2 to 3 hours.

Distribution

Pioglitazone hydrochloride

The mean apparent volume of distribution (Vd/F) of pioglitazone following single-dose administration is 0.63 ± 0.41 (mean ± SD) L/kg of body weight. Pioglitazone is extensively protein bound ( > 99%) in human serum, principally to serum albumin. Pioglitazone also binds to other serum proteins, but with lower affinity. Metabolites M-III and M-IV also are extensively bound ( > 98%) to serum albumin.

Glimepiride

After intravenous (IV) dosing in normal subjects, Vd/F was 8.8 L (113 mL/kg), and the total body clearance (CL) was 47.8 mL/min. Protein binding was greater than 99.5%.

Metabolism

Pioglitazone hydrochloride

Pioglitazone is extensively metabolized by hydroxylation and oxidation; the metabolites also partly convert to glucuronide or sulfate conjugates. Metabolites M-II and M-IV (hydroxy derivatives of pioglitazone) and M-III (keto derivative of pioglitazone) are pharmacologically active in animal models of type 2 diabetes. In addition to pioglitazone, M-III and M-IV are the principal drug-related species found in human serum following multiple dosing. At steady-state, in both healthy volunteers and in patients with type 2 diabetes, pioglitazone comprises approximately 30% to 50% of the total peak serum concentrations and 20% to 25% of the total AUC.

In vitro data demonstrate that multiple CYP isoforms are involved in the metabolism of pioglitazone. The cytochrome P450 isoforms involved are CYP2C8 and, to a lesser degree, CYP3A4 with additional contributions from a variety of other isoforms including the mainly extrahepatic CYP1A1. In vivo studies of pioglitazone in combination with P450 inhibitors and substrates have been performed (see PRECAUTIONS: DRUG INTERACTIONS, Pioglitazone hydrochloride). Urinary 6ß-hydroxycortisol/cortisol ratios measured in patients treated with pioglitazone showed that pioglitazone is not a strong CYP3A4 enzyme inducer.

Glimepiride

Glimepiride is completely metabolized by oxidative biotransformation after either an IV or oral dose. The major metabolites are the cyclohexyl hydroxy methyl derivative (M1) and the carboxyl derivative (M2). CYP2C9 has been shown to be involved in the biotransformation of glimepiride to M1. M1 is further metabolized to M2 by one or several cytosolic enzymes. M1, but not M2, possesses about 1/3 of the pharmacological activity as compared to its parent in an animal model; however, whether the glucose-lowering effect of M1 is clinically meaningful is not clear.

Excretion and Elimination

Pioglitazone hydrochloride

Following oral administration, approximately 15% to 30% of the pioglitazone dose is recovered in the urine. Renal elimination of pioglitazone is negligible and the drug is excreted primarily as metabolites and their conjugates. It is presumed that most of the oral dose is excreted into the bile either unchanged or as metabolites and eliminated in the feces.

The mean serum half-life of pioglitazone and total pioglitazone ranges from 3 to 7 hours and 16 to 24 hours, respectively. Pioglitazone has an apparent clearance, CL/f, calculated to be 5 to 7 L/hr.

Glimepiride

When ¹⁴C-glimepiride was given orally, approximately 60% of the total radioactivity was recovered in the urine in 7 days and M1 (predominant) and M2 accounted for 80-90% of that recovered in the urine. Approximately 40% of the total radioactivity was recovered in feces and M1 and M2 (predominant) accounted for about 70% of that recovered in feces. No parent drug was recovered from urine or feces. After IV dosing in patients, no significant biliary excretion of glimepiride or its M1 metabolite has been observed.

Special Populations

Renal Insufficiency

Pioglitazone hydrochloride

The serum elimination half-life of pioglitazone, M-III and M-IV remains unchanged in patients with moderate (creatinine clearance 30 to 60 mL/min) to severe (creatinine clearance < 30 mL/min) renal impairment when compared to normal subjects. No dose adjustment in patients with renal dysfunction is recommended.

Glimepiride

A single-dose, open-label study was conducted in 15 patients with renal impairment. Glimepiride (3 mg) was administered to 3 groups of patients with different levels of mean creatinine clearance (CLcr); (Group I, CLcr = 77.7 mL/min, n = 5), (Group II, CLcr = 27.7 mL/min, n = 3), and (Group III, CLcr = 9.4 mL/min, n = 7). Glimepiride was found to be well tolerated in all 3 groups. The results showed that glimepiride serum levels decreased as renal function decreased. However, M1 and M2 serum levels (mean AUC values) increased 2.3 and 8.6 times from Group I to Group III. The apparent terminal half-life (T½) for glimepiride did not change, while the half-lives for M1 and M2 increased as renal function decreased. Mean urinary excretion of M1 plus M2 as percent of dose, however, decreased (44.4%, 21.9%, and 9.3% for Groups I to III).

A multiple-dose titration study was also conducted in 16 patients with type 2 diabetes and with renal impairment using doses ranging from 1-8 mg daily for 3 months. The results were consistent with those observed after single doses. All patients with a CLcr less than 22 mL/min had adequate control of their glucose levels with a dosage regimen of only 1 mg daily. The results from this study suggested that a starting dose of 1 mg glimepiride may be given to patients with type 2 diabetes and kidney disease, and the dose may be titrated based on fasting blood glucose levels (see DOSAGE AND ADMINISTRATION, Special Patient Populations).

Hepatic Insufficiency

Pioglitazone hydrochloride

Compared with normal controls, subjects with impaired hepatic function (Child-Pugh Grade B/C) have an approximate 45% reduction in pioglitazone and total pioglitazone mean peak concentrations but no change in the mean AUC values.

Therapy with DUETACT should not be initiated if the patient exhibits clinical evidence of active liver disease or serum transaminase levels (ALT) exceed 2.5 times the upper limit of normal (see PRECAUTIONS, General: Pioglitazone hydrochloride, Hepatic Effects).

Glimepiride

No studies were performed in patients with hepatic insufficiency.

Elderly

Pioglitazone hydrochloride

In healthy elderly subjects, peak serum concentrations of pioglitazone and total pioglitazone are not significantly different, but AUC values are slightly higher and the terminal half-life values slightly longer than for younger subjects. These changes were not of a magnitude that would be considered clinically relevant.

Glimepiride

Comparison of glimepiride pharmacokinetics in patients with type 2 diabetes ≤ 65 years and those > 65 years was performed in a study using a dosing regimen of 6 mg daily. There were no significant differences in glimepiride pharmacokinetics between the two age groups. The mean AUC at steady-state for the older patients was about 13% lower than that for the younger patients; the mean weight-adjusted clearance for the older patients was about 11% higher than that for the younger patients.

Pediatrics:

No pharmacokinetic studies of DUETACT were performed in pediatric patients.

Gender

Pioglitazone hydrochloride

As monotherapy and in combination with sulfonylurea, metformin, or insulin, pioglitazone improved glycemic control in both males and females. The mean Cmax and AUC values were increased 20% to 60% in females. In controlled clinical trials, hemoglobin A1C (A1C) decreases from baseline were generally greater for females than for males (average mean difference in A1C 0.5%). Since therapy should be individualized for each patient to achieve glycemic control, no dose adjustment is recommended based on gender alone.

Glimepiride

There were no differences between males and females in the pharmacokinetics of glimepiride when adjustment was made for differences in body weight.

Ethnicity

Pioglitazone hydrochloride

Pharmacokinetic data among various ethnic groups are not available.

Glimepiride

No pharmacokinetic studies to assess the effects of race have been performed, but in placebo-controlled studies of glimepiride in patients with type 2 diabetes, the antihyperglycemic effect was comparable in whites (n = 536), blacks (n = 63), and Hispanics (n = 63).

Other Populations

Glimepiride

There were no important differences in glimepiride metabolism in subjects identified as phenotypically different drug-metabolizers by their metabolism of sparteine. The pharmacokinetics of glimepiride in morbidly obese patients were similar to those in the normal weight group, except for a lower Cmax and AUC. However, since neither Cmax nor AUC values were normalized for body surface area, the lower values of Cmax and AUC for the obese patients were likely the result of their excess weight and not due to a difference in the kinetics of glimepiride.

Drug-Drug Interactions

Co-administration of pioglitazone (45 mg) and a sulfonylurea (5 mg glipizide) administered orally once daily for 7 days did not alter the steady-state pharmacokinetics of glipizide. Glimepiride and glipizide have similar metabolic pathways and are mediated by CYP2C9; therefore, drug-drug interaction between pioglitazone and glimepiride is considered unlikely. Specific pharmacokinetic drug interaction studies with DUETACT have not been performed, although such studies have been conducted with the individual pioglitazone and glimepiride components.

Pioglitazone hydrochloride

The following drugs were studied in healthy volunteers with co-administration of pioglitazone 45 mg once daily. Results are listed below:

Oral Contraceptives: Co-administration of pioglitazone (45 mg once daily) and an oral contraceptive (1 mg norethindrone plus 0.035 mg ethinyl estradiol once daily) for 21 days, resulted in 11% and 11-14% decrease in ethinyl estradiol AUC (0-24h) and Cmax respectively. There were no significant changes in norethindrone AUC (0-24h) and Cmax. In view of the high variability of ethinyl estradiol pharmacokinetics, the clinical significance of this finding is unknown.

Midazolam: Administration of pioglitazone for 15 days followed by a single 7.5 mg dose of midazolam syrup resulted in a 26% reduction in midazolam Cmax and AUC.

Nifedipine ER: Co-administration of pioglitazone for 7 days with 30 mg nifedipine ER administered orally once daily for 4 days to male and female volunteers resulted in a ratio of least square mean (90% CI) values for unchanged nifedipine of 0.83 (0.73 -0.95) for Cmax and 0.88 (0.80 -0.96) for AUC. In view of the high variability of nifedipine pharmacokinetics, the clinical significance of this finding is unknown.

Ketoconazole: Co-administration of pioglitazone for 7 days with ketoconazole 200 mg administered twice daily resulted in a ratio of least square mean (90% CI) values for unchanged pioglitazone of 1.14 (1.06 -1.23) for Cmax, 1.34 (1.26 -1.41) for AUC and 1.87 (1.71 -2.04) for Cmin.

Atorvastatin Calcium: Co-administration of pioglitazone for 7 days with atorvastatin calcium (LIPITOR®) 80 mg once daily resulted in a ratio of least square mean (90% CI) values for unchanged pioglitazone of 0.69 (0.57 -0.85) for Cmax, 0.76 (0.65 -0.88) for AUC and 0.96 (0.87 -1.05) for Cmin. For unchanged atorvastatin, the ratio of least square mean (90% CI) values were 0.77 (0.66 -0.90) for Cmax, 0.86 (0.78 -0.94) for AUC and 0.92 (0.82 -1.02) for Cmin.

Cytochrome P450: See PRECAUTIONS: DRUG INTERACTIONS, Pioglitazone hydrochloride

Gemfibrozil: Concomitant administration of gemfibrozil (oral 600 mg twice daily), an inhibitor of CYP2C8, with pioglitazone (oral 30 mg) in 10 healthy volunteers pre-treated for 2 days prior with gemfibrozil (oral 600 mg twice daily) resulted in pioglitazone exposure (AUC0-24) being 226% of the pioglitazone exposure in the absence of gemfibrozil (see PRECAUTIONS: DRUG INTERACTIONS, Pioglitazone hydrochloride).¹

Rifampin: Concomitant administration of rifampin (oral 600 mg once daily), an inducer of CYP2C8 with pioglitazone (oral 30 mg) in 10 healthy volunteers pre-treated for 5 days prior with rifampin (oral 600 mg once daily) resulted in a decrease in the AUC of pioglitazone by 54% (see PRECAUTIONS: DRUG INTERACTIONS, Pioglitazone hydrochloride).²

In other drug-drug interaction studies, pioglitazone had no significant effect on the pharmacokinetics of fexofenadine, metformin, digoxin, warfarin, ranitidine, or theophylline.

Glimepiride

The hypoglycemic action of sulfonylureas may be potentiated by certain drugs, including nonsteroidal anti-inflammatory drugs and other drugs that are highly protein bound, such as salicylates, sulfonamides, chloramphenicol, coumarins, probenecid, monoamine oxidase inhibitors, and beta adrenergic blocking agents. Due to the potential drug interaction between these drugs and glimepiride, the patient should be observed closely for hypoglycemia when these drugs are co-administered. Conversely, when these drugs are withdrawn, the patient should be observed closely for loss of glycemic control.

Certain drugs tend to produce hyperglycemia and may lead to loss of control. These drugs include the thiazides and other diuretics, corticosteroids, phenothiazines, thyroid products, estrogens, oral contraceptives, phenytoin, nicotinic acid, sympathomimetics, and isoniazid. Due to the potential drug interaction between these drugs and glimepiride, the patient should be observed closely for loss of glycemic control when these drugs are co-administered. Conversely, when these drugs are withdrawn, the patient should be observed closely for hypoglycemia.

Aspirin: Co-administration of aspirin (1 g three times daily) and glimepiride led to a 34% decrease in the mean glimepiride AUC and, therefore, a 34% increase in the mean CL/f. The mean Cmax had a decrease of 4%. Blood glucose and serum C-peptide concentrations were unaffected and no hypoglycemic symptoms were reported. Pooled data from clinical trials showed no evidence of clinically significant adverse interactions with uncontrolled concurrent administration of aspirin and other salicylates.

Cimetidine/Ranitidine: Co-administration of either cimetidine (800 mg once daily) or ranitidine (150 mg twice daily) with a single 4-mg oral dose of glimepiride did not significantly alter the absorption and disposition of glimepiride, and no differences were seen in hypoglycemic symptomatology. Pooled data from clinical trials showed no evidence of clinically significant adverse interactions with uncontrolled concurrent administration of H2-receptor antagonists.

Propranolol: Concomitant administration of propranolol (40 mg three times daily) and glimepiride significantly increased Cmax, AUC, and T½ of glimepiride by 23%, 22%, and 15%, respectively, and it decreased CL/f by 18%. The recovery of M1 and M2 from urine, however, did not change. The pharmacodynamic responses to glimepiride were nearly identical in normal subjects receiving propranolol and placebo. Pooled data from clinical trials in patients with type 2 diabetes showed no evidence of clinically significant adverse interactions with uncontrolled concurrent administration of beta-blockers. However, if beta-blockers are used, caution should be exercised and patients should be warned about the potential for hypoglycemia.

Warfarin: Concomitant administration of glimepiride (4 mg once daily) did not alter the pharmacokinetic characteristics of R-and S-warfarin enantiomers following administration of a single dose (25 mg) of racemic warfarin to healthy subjects. No changes were observed in warfarin plasma protein binding. Glimepiride treatment did result in a slight, but statistically significant, decrease in the pharmacodynamic response to warfarin. The reductions in mean area under the prothrombin time (PT) curve and maximum PT values during glimepiride treatment were very small (3.3% and 9.9%, respectively) and are unlikely to be clinically important.

Ramipril: The responses of serum glucose, insulin, C-peptide, and plasma glucagon to 2 mg glimepiride were unaffected by co-administration of ramipril (an ACE inhibitor) 5 mg once daily in normal subjects. No hypoglycemic symptoms were reported. Pooled data from clinical trials in patients with type 2 diabetes showed no evidence of clinically significant adverse interactions with uncontrolled concurrent administration of ACE inhibitors.

Miconazole: A potential interaction between oral miconazole and oral hypoglycemic agents leading to severe hypoglycemia has been reported. Whether this interaction also occurs with the intravenous, topical, or vaginal preparations of miconazole is not known. There is a potential interaction of glimepiride with inhibitors (e.g. fluconazole) and inducers (e.g. rifampicin) of cytochrome P450 2C9.

Although no specific interaction studies were performed with glimepiride, pooled data from clinical trials showed no evidence of clinically significant adverse interactions with uncontrolled concurrent administration of calcium-channel blockers, estrogens, fibrates, NSAIDS, HMG CoA reductase inhibitors, sulfonamides, or thyroid hormone.

Pharmacodynamics and Clinical Effects

Pioglitazone hydrochloride

Clinical studies demonstrate that pioglitazone improves insulin sensitivity in insulin-resistant patients. Pioglitazone enhances cellular responsiveness to insulin, increases insulin-dependent glucose disposal, improves hepatic sensitivity to insulin, and improves dysfunctional glucose homeostasis. In patients with type 2 diabetes, the decreased insulin resistance produced by pioglitazone results in lower plasma glucose concentrations, lower plasma insulin levels, and lower A1C values. Based on results from an open-label extension study, the glucose-lowering effects of pioglitazone appear to persist for at least one year. In controlled clinical studies, pioglitazone in combination with a sulfonylurea had an additive effect on glycemic control.

Patients with lipid abnormalities were included in placebo-controlled monotherapy clinical studies with pioglitazone. Overall, patients treated with pioglitazone had mean decreases in triglycerides, mean increases in HDL cholesterol, and no consistent mean changes in LDL cholesterol and total cholesterol compared to the placebo group. A similar pattern of results was seen in 16-week and 24-week combination therapy studies of pioglitazone with a sulfonylurea.

Glimepiride

A mild glucose-lowering effect first appeared following single oral doses as low as 0.5-0.6 mg in healthy subjects. The time required to reach the maximum effect (i.e., minimum blood glucose level [Tmin]) was about 2 to 3 hours. In patients with type 2 diabetes, both fasting and 2-hour postprandial glucose levels were significantly lower with glimepiride (1, 2, 4, and 8 mg once daily) than with placebo after 14 days of oral dosing. The glucose-lowering effect in all active treatment groups was maintained over 24 hours.

In larger dose-ranging studies, blood glucose and A1C were found to respond in a dose-dependent manner over the range of 1 to 4 mg/day of glimepiride. Some patients, particularly those with higher fasting plasma glucose (FPG) levels, may benefit from doses of glimepiride up to 8 mg once daily. No difference in response was found when glimepiride was administered once or twice daily.

In two 14-week, placebo-controlled studies in 720 subjects, the average net reduction in A1C for patients treated with 8 mg of glimepiride once daily was 2.0% in absolute units compared with placebo-treated patients. In a long-term, randomized, placebo-controlled study of patients with type 2 diabetes unresponsive to dietary management, glimepiride therapy improved postprandial insulin/C-peptide responses, and 75% of patients achieved and maintained control of blood glucose and A1C. Efficacy results were not affected by age, gender, weight, or race. In long-term extension trials with previously-treated patients, no meaningful deterioration in mean fasting plasma glucose (FPG) or A1C levels was seen after 2 ½ years of glimepiride therapy.

Glimepiride therapy is effective in controlling blood glucose without deleterious changes in the plasma lipoprotein profiles of patients treated for type 2 diabetes.

Clinical Studies

There have been no clinical efficacy studies conducted with DUETACT. However, the efficacy and safety of the separate components have been previously established. The co-administration of pioglitazone and a sulfonylurea, including glimepiride, has been evaluated for efficacy and safety in two clinical studies. These clinical studies established an added benefit of pioglitazone in glycemic control of patients with inadequately controlled type 2 diabetes while on sulfonylurea therapy. Bioequivalence of DUETACT with co-administered pioglitazone and glimepiride tablets was demonstrated at the 30 mg/2 mg and 30 mg/4 mg dosage strengths (see CLINICAL PHARMACOLOGY, Pharmacokinetics and Drug Metabolism, Absorption and Bioavailability).

Clinical Studies of Pioglitazone Add-On Therapy in Patients Not Adequately Controlled on a Sulfonylurea

Two treatment-randomized, controlled clinical studies in patients with type 2 diabetes were conducted to evaluate the safety and efficacy of pioglitazone plus a sulfonylurea. Both studies included patients receiving a sulfonylurea, either alone or in combination with another antihyperglycemic agent, who had inadequate glycemic control. Excluding the sulfonylurea agent, all other antihyperglycemic agents were discontinued prior to starting study treatment. In the first study, 560 patients were randomized to receive 15 mg or 30 mg of pioglitazone or placebo once daily in addition to their current sulfonylurea regimen for 16 weeks. In the second study, 702 patients were randomized to receive 30 mg or 45 mg of pioglitazone once daily in addition to their current sulfonylurea regimen for 24 weeks.

In the first study, the addition of pioglitazone 15 mg or 30 mg once daily to treatment with a sulfonylurea after 16 weeks significantly reduced the mean A1C by 0.88% and 1.28% and the mean FPG by 39.4 mg/dL and 57.9 mg/dL, respectively, from that observed with sulfonylurea treatment alone. In the second study, the mean reductions from baseline at Week 24 in A1C were 1.55% and 1.67% for the 30 mg and 45 mg doses, respectively. Mean reductions from baseline in FPG were 51.5 mg/dL and 56.1 mg/dL, respectively. Based on these reductions in A1C and FPG (Table 2), the addition of pioglitazone to sulfonylurea resulted in significant improvements in glycemic control irrespective of the sulfonylurea dosage.

Table 2. Glycemic Parameters in 16-Week and 24-Week Pioglitazone Hydrochloride + Sulfonylurea Combination Studies

Parameter	Placebo + sulfonylurea	Pioglitazone 15 mg + sulfonylurea	Pioglitazone 30 mg + sulfonylurea
16-Week Study
A1C (%)	N=181	N=176	N=182
Baseline mean	9.86	10.01	9.93
Mean change from baseline at 16 weeks	0.06	-0.82*†	-1.22*†
Difference in change from placebo +sulfonylurea		-0.88	-1.28
Responder rate (%)a	23.8	56.8	74.2
FPG (mg/dL)	N=182	N=179	N=186
Baseline mean	236	246.8	238.9
Mean change from baseline at 16 weeks	5.6	-33.8*†	-52.3*†
Difference in change from placebo +sulfonylurea		-39.4	-57.9
Responder rate (%)b	22.0	55.3	67.7
Parameter	Pioglitazone 30 mg + sulfonylurea	Pioglitazone 45 mg + sulfonylurea
24-Week Study
A1C (%)	N=340	N=332
Baseline mean	9.77	9.85
Mean change from baseline at 24 weeks	-1.55*	-1.67*
Responder rate (%)a	77.4	79.5
FPG (mg/dL)	N=338	N=329
Baseline mean	214.4	217.2
Mean change from baseline at 24 weeks	-51.5*	-56.1*
Responder rate (%)b	63.6	71.1
* significant change from baseline p ≤ 0.050 † significant difference from placebo plus sulfonylurea, p ≤ 0.050 a patients who achieved an A1C ≤ 6.1% or ≥ 0.6% decrease from baseline b patients who achieved a decrease in FPG by ≥ 30 mg/dL

Animal Toxicology

Pioglitazone hydrochloride

Heart enlargement has been observed in mice (100 mg/kg), rats (4 mg/kg and above) and dogs (3 mg/kg) treated orally with pioglitazone hydrochloride (approximately 11, 1, and 2 times the maximum recommended human oral dose for mice, rats, and dogs, respectively, based on mg/m²). In a one-year rat study, drug-related early death due to apparent heart dysfunction occurred at an oral dose of 160 mg/kg/day (approximately 35 times the maximum recommended human oral dose based on mg/m²). Heart enlargement was seen in a 13-week study in monkeys at oral doses of 8.9 mg/kg and above (approximately 4 times the maximum recommended human oral dose based on mg/m²), but not in a 52-week study at oral doses up to 32 mg/kg (approximately 13 times the maximum recommended human oral dose based on mg/m²).

Glimepiride

Reduced serum glucose values and degranulation of the pancreatic beta cells were observed in beagle dogs exposed to 320 mg glimepiride/kg/day for 12 months (approximately 1,000 times the recommended human dose based on surface area). No evidence of tumor formation was observed in any organ. One female and one male dog developed bilateral subcapsular cataracts. Non-GLP studies indicated that glimepiride was unlikely to exacerbate cataract formation. Evaluation of the co-cataractogenic potential of glimepiride in several diabetic and cataract rat models was negative and there was no adverse effect of glimepiride on bovine ocular lens metabolism in organ culture.

Human Ophthalmology Data

Glimepiride

Ophthalmic examinations were carried out in over 500 subjects during long-term studies using the methodology of Taylor and West and Laties et al. No significant differences were seen between glimepiride and glyburide in the number of subjects with clinically important changes in visual acuity, intraocular tension, or in any of the five lens-related variables examined.

Ophthalmic examinations were carried out during long-term studies using the method of Chylack et al. No significant or clinically meaningful differences were seen between glimepiride and glipizide with respect to cataract progression by subjective LOCS II grading and objective image analysis systems, visual acuity, intraocular pressure, and general ophthalmic examination.

REFERENCES

1. Deng, LJ, et al. Effect of gemfibrozil on the pharmacokinetics of pioglitazone. Eur J Clin Pharmacol 2005; 61: 831-836, Table 1.

2. Jaakkola, T, et al. Effect of rifampicin on the pharmacokinetics of pioglitazone. Br J Clin Pharmacol 2006; 61:1 70-78.

Last reviewed on RxList: 8/12/2011
This monograph has been modified to include the generic and brand name in many instances.