BACKGROUND: Combination oral therapy is often used to control the hyperglycemia of patients with type 2 diabetes. We compared the effectiveness of metformin and troglitazone when added to sulfonylurea therapy for patients with type 2 diabetes who had suboptimal blood glucose control.
METHODS: We used a randomized 2-group design to compare the efficacy, safety, and tolerability of troglitazone and metformin for patients with type 2 diabetes mellitus that was inadequately controlled with diet and oral sulfonylureas. Thirty-two subjects were randomized to receive either troglitazone or metformin for 14 weeks, including a 2-week drug-titration period. The primary outcome variable was mean change in the level of glycosylated hemoglobin (Hb A1c) from baseline. Secondary outcomes included mean changes from baseline in fasting plasma glucose and C-peptide levels, renal or metabolic side effects, and symptomatic tolerability.
RESULTS: The addition of either troglitazone or metformin to oral sulfonylurea therapy significantly decreased Hb A1c levels. Both treatment regimens also significantly reduced fasting plasma glucose and C-peptide levels. We found no significant differences between the treatment arms in efficacy, metabolic side effects, or tolerability.
CONCLUSIONS: Our results demonstrate that troglitazone and metformin each significantly improved Hb A1c, fasting plasma glucose, and C-peptide levels when added to oral sulfonylurea therapy for patients with type 2 diabetes who had inadequate glucose control.
In 1998 an estimated 9.5 million people had a diagnosis of type 2 diabetes mellitus in the United States.1 Tight control of blood glucose concentrations to near-normal levels has been shown to reduce the microvascular complications of type 2 diabetes without increasing major macrovascular complications.2,3 However, control of blood glucose is complex and involves multiple organ systems. Patients with type 2 diabetes often do not achieve desirable glucose control despite the use of oral hypoglycemic agents or insulin. Insulin resistance—the diminished ability of insulin to exert its biological activity over a broad range of glucose levels—may contribute to the difficulty in controlling type 2 diabetes.4,5
Thiazolidinediones represent a newer class of drugs that affect insulin resistance.6,7 Troglitazone (Rezulin) is the first drug in this class to be approved by the US Food and Drug Administration (FDA) for the treatment of type 2 diabetes. Troglitazone can be used in combination with a sulfonylurea or insulin to improve glycemic control.8-10 Troglitazone increases the responsiveness of insulin-dependent tissues through a mechanism thought to involve receptors that regulate the transcription of a number of insulin-responsive genes.11,12 It increases insulin-dependent glucose disposal in skeletal muscle, enhancing the effects of circulating insulin.
Metformin (glucophage) lowers plasma glucose by decreasing hepatic glucose output through the inhibition of gluconeogenesis and by increasing peripheral glucose use by skeletal muscle. It is a biguanide that was introduced in Europe in 1957 and has been available in the United States since 1995.13,14 Metformin is indicated in patients with type 2 diabetes as a monotherapy along with diet; it can also be used concomitantly with a sulfonylurea or insulin.15,16 The efficacy of metformin on glycemic control has been demonstrated as a monotherapy and in combination with a sulfonylurea.16,17
Although there are data to support the use of metformin or troglitazone in combination with a sulfonylurea,8-10,14-16 randomized comparisons of the relative effects of these combinations on glycemic control are lacking. Information about the efficacy, safety, tolerability, and cost of these combination therapies may help in pharmacotherapy decision making. Our primary goal was to compare the effects of troglitazone with those of metformin on the Hb A1c levels of patients with type 2 diabetes who were already receiving sulfonylurea therapy. Secondary outcomes included the comparative effects of these combinations on fasting plasma glucose (FPG) and C-peptide levels. We also compared safety, tolerability, and cost of the 2 drugs.
Methods
Study Subjects
We studied 32 patients (20 men, 12 women) with type 2 diabetes who were already taking a sulfonylurea. We randomly screened individuals found in a database of family medicine patients who had been given a diagnosis of type 2 diabetes mellitus. Patients were eligible if they were aged 30 to 75 years, had poorly controlled diabetes defined by an Hb A1c level between 8.5% and 16% at the screening visit, and were able to give informed consent. We excluded women of childbearing potential. The other exclusion criteria were: a history or laboratory evidence of renal or hepatic insufficiency; a history of alcohol abuse (including binge drinking within the past year); concomitant treatment with insulin, cholestyramine, potentially nephrotoxic drugs, or glucocorticoids (except topical or inhaled glucocorticoids); plans for radiographic studies involving the use of intravenous iodinated contrast during the course of our study; and known intolerance or sensitivity to a biguanide or troglitazone. The protocol was approved by the institutional review board at Wake Forest University Baptist Medical Center.