Sulphonylurea treatment of NIDDM patients with cardiovascular disease: a mixed blessing?

Pharmacological treatment of diabetic patients with cardiovascular complications

Cardiovascular complications are frequently present in insulin-dependent (IDDM) and non-insulin dependent diabetes mellitus (NIDDM) patients and confer a very poor prognosis. In this overview we critically analyse the current literature with regard to the benefits and also the possible harms of the available pharmacological treatment strategies in these patients. To date, insulin is the only hypoglycaemic agent which has been proven both effective and safe in NIDDM patients with cardiovascular complications. Also, several trials indicate that treatment with oral hypoglycaemic agents may confer a substantial risk in such patients. Conventional antihypertensive treatment, including betablockers and diuretics, has been convincingly shown to reduce mortality and morbidity in diabetic nephropathy and in NIDDM patients. However, this may not be the case with newer antihypertensive agents, such as angiotensin-converting enzyme (ACE) inhibitors and calcium channel blockers. Likewise, convincing evidence is lacking that these newer antihypertensive agents provide meaningful clinical benefit when compared to the conventional treatment regarding slower progression of diabetic nephropathy or their impact on lipid and glucose metabolism. Cholesterol lowering therapy with statins and aspirin treatment have also been repeatedly shown to improve the prognosis of diabetic patients with coronary heart disease.

Acarbose in ambulatory treatment of non-insulin-dependent diabetes mellitus associated to imminent sulfonylurea failure: a randomised-multicentric trial in primary health-care. Diabetes and Acarbose Research Group

To assess the efficacy and safety of acarbose as an adjunct to high sulfonylurea (SU) doses in patients with imminent SU failure, a randomised, multicentric, 6 month double-blind, parallel and placebo-controlled trial was performed in primary healthcare. Entry criteria were: NIDDM patients in concomitant dietary follow-up, age > 40 year-old, more than 3 years of diagnosed diabetes, baseline HbAlc levels between 8-12% (N: 4-6%), stable body mass index < 35 kg m-2 and glibenclamide daily dose > 10 mg. After 1 month placebo run-in period all patients were randomly allocated into two groups of treatment (acarbose 100 mg t.i.d. vs placebo). HbAlc levels, the main efficacy variable, lipid profile, fasting and postprandial blood glucose levels were performed and adverse events were also recorded. A total number of 65 patients were randomised, 36 in acarbose and 29 in a placebo group. No statistical differences were found on age (60.2/61.7 year-old), BMI (28.7/27.4 kg m-2), glibenclamide dose (14.5/14.0 mg/day) and baseline HbAlc (9.0/8.8%). Acarbose-treated patients significantly reduced HbAlc levels (9.0/7.9 vs 8.8/8.5%; P < 0.01), based upon a marked decrease, but statistically not significant, in mean postprandial plasma glucose levels (11.9/9.6 vs 12.4/11.1 mmol l-1). No significant differences between fasting plasma glucose and lipid profile were detected. A total of 31 patients (47.7%) reported adverse events, 20 (55.5%) and 11 (37.9%) in acarbose and placebo treatment group respectively. Relationship with drug was estimated as possible or probable in 16 (44.4%) of acarbose-treated patients. None of them were excluded from study participation due to insulin requirement. Only seven patients (10.7%), six with acarbose (16.6%) and one with placebo (3.8%), withdrew the study because of the adverse events. Thus, acarbose seems to be a useful option in order to improve HbAlc levels in non-insulin-dependent diabetes mellitus with imminent sulfonylurea failure.

Drug treatment of non-insulin-dependent diabetes mellitus in the 1990s. Achievements and future developments

Non-insulin-dependent diabetes mellitus (NIDDM, type 2 diabetes) is a heterogeneous disease resulting from a dynamic interaction between defects in insulin secretion and insulin action. There are various pharmacological approaches to improving glucose homeostasis, but those currently used in clinical practice either do not succeed in restoring normoglycaemia in most patients or fail after a variable period of time. For glycaemic regulation, 4 classes of drugs are currently available: sulphonylureas, biguanides (metformin), alpha-glucosidase inhibitors (acarbose) and insulin, each of which has a different mode and site of action. These standard pharmacological treatments may be used individually for certain types of patients, or may be combined in a stepwise fashion to provide more ideal glycaemic control for most patients. Adjunct treatments comprise a few pharmacological approaches which may help to improve glycaemic control by correcting some abnormalities frequently associated with NIDDM, such as obesity (serotoninergic anorectic agents) and hyperlipidaemia (benfluorex). There is intensive pharmaceutical research to find new drugs able to stimulate insulin secretion (new sulphonylurea or nonsulphonylurea derivatives, glucagon-like peptide-1), improve insulin action (thiazolidinediones, lipid interfering agents, glucagon antagonists, vanadium compounds) or reduce carbohydrate absorption (miglitol, amylin analogues, glucagon-like peptide-1). Further studies should demonstrate the superiority of these new compounds over the standard antidiabetic agents as well as their optimal mode of administration, alone or in combination with currently available drugs.

Sulfonylureas

Sulfonylureas have been available for the treatment of non-insulin-dependent diabetes mellitus (NIDDM) since the 1950s. With the introduction of new oral agents, there is a tendency to discount the value of sulfonylurea therapy. Sulfonylureas have the advantage of multiple formulations, low costs, minimal side effects, and demonstrated efficacy in controlling hyperglycemia. The major disadvantage of sulfonylureas is secondary failure, which may occur with all oral agents as part of the progression of NIDDM. Sulfonylureas should continue to play an important role in the treatment of NIDDM.

Effects of tolbutamide on ATP-sensitive K+ channels from human right atrial cardiac myocytes

In order to gain further insight into possible deleterious effects on ischaemia-induced myocardial damage induced by sulfonylureas when administered to humans, the effects of tolbutamide on ATP-sensitive K+ (KATP) channels from human right atrial myocytes were studied. Single myocytes were enzymatically isolated from human right atrium. The cell-attached and inside-out configuration of the patch-clamp technique were employed at room temperature (both the pipette and the bath solution contained high [K+]). KATP channels in inside-out patches showed slight inward rectification, had a slope conductance of 75.1 +/- 2.4 pS (mean +/- S.E.M.; n = 5) at negative membrane potentials and these channels were blocked by ATP (half-maximal block (EC50) at 39 microM; Hill coefficient = 1.65). In cell-attached recordings, cromakalim (300 microM) opened KATP channels (with a slope conductance of 73.3 +/- 1.8 pS (n = 16) at negative membrane potentials) in previously silent patches. Cromakalim-induced openings of KATP channels were not markedly affected by 100 or 300 microM tolbutamide but were blocked by tolbutamide at millimolar concentrations (1-3 mM). The concentration-response relationship for tolbutamide-induced block of KATP channels in the presence of 300 microM cromakalim in cell-attached patches was calculated to values for the EC50 of 1.325 mM and for the Hill coefficient of 1.0, respectively. 1 mM tolbutamide-induced block of cromakalim-induced KATP channel openings was not different at room temperature when compared to 37 degrees. It is concluded that KATP channels from human right atrial myocytes have a low sensitivity towards tolbutamide-induced block.