Acarbose

ACARBOSE — acarbose tablet
Physicians Total Care, Inc.

Rx only

DESCRIPTION

Acarbose Tablets are an oral alpha-glucosidase inhibitor for use in the management of type 2 diabetes mellitus. Acarbose is an oligosaccharide which is obtained from fermentation processes of a microorganism, Actinoplanes utahensis, and is chemically known as O- 4,6-dideoxy-4-[[(1S,4R,5S,6S)-4,5,6-trihydroxy-3-(hydroxymethyl)-2-cyclohexen-1-yl]amino]-α-D- glucopyranosyl-(1→4)-O -α-D-glucopyranosyl-(1→4)-D-glucose. It is a white to off-white powder with a molecular weight of 645.6. Acarbose is soluble in water and has a pK_a of 5.1. Its molecular formula is C₂₅ H₄₃ NO₁₈ and its chemical structure is as follows:

Acarbose Tablets are available as 25 mg, 50 mg and 100 mg tablets for oral use. The inactive ingredients are colloidal silicon dioxide, corn starch, magnesium stearate and microcrystalline cellulose.

CLINICAL PHARMACOLOGY

Acarbose is a complex oligosaccharide that delays the digestion of ingested carbohydrates, thereby resulting in a smaller rise in blood glucose concentration following meals. As a consequence of plasma glucose reduction, acarbose reduces levels of glycosylated hemoglobin in patients with type 2 diabetes mellitus. Systemic non-enzymatic protein glycosylation, as reflected by levels of glycosylated hemoglobin, is a function of average blood glucose concentration over time.

Mechanism of Action

In contrast to sulfonylureas, acarbose does not enhance insulin secretion. The antihyperglycemic action of acarbose results from a competitive, reversible inhibition of pancreatic alpha-amylase and membrane-bound intestinal alpha-glucoside hydrolase enzymes. Pancreatic alpha-amylase hydrolyzes complex starches to oligosaccharides in the lumen of the small intestine, while the membrane-bound intestinal alpha-glucosidases hydrolyze oligosaccharides, trisaccharides, and disaccharides to glucose and other monosaccharides in the brush border of the small intestine. In diabetic patients, this enzyme inhibition results in a delayed glucose absorption and a lowering of postprandial hyperglycemia.

Because its mechanism of action is different, the effect of acarbose to enhance glycemic control is additive to that of sulfonylureas, insulin or metformin when used in combination. In addition, acarbose diminishes the insulinotropic and weight-increasing effects of sulfonylureas.

Acarbose has no inhibitory activity against lactase and consequently would not be expected to induce lactose intolerance.

Pharmacokinetics

Absorption

In a study of 6 healthy men, less than 2% of an oral dose of acarbose was absorbed as active drug, while approximately 35% of total radioactivity from a ¹⁴ C-labeled oral dose was absorbed. An average of 51% of an oral dose was excreted in the feces as unabsorbed drug-related radioactivity within 96 hours of ingestion. Because acarbose acts locally within the gastrointestinal tract, this low systemic bioavailability of parent compound is therapeutically desired. Following oral dosing of healthy volunteers with ¹⁴ C-labeled acarbose, peak plasma concentrations of radioactivity were attained 14 to 24 hours after dosing, while peak plasma concentrations of active drug were attained at approximately 1 hour. The delayed absorption of acarbose-related radioactivity reflects the absorption of metabolites that may be formed by either intestinal bacteria or intestinal enzymatic hydrolysis.

Metabolism

Acarbose is metabolized exclusively within the gastrointestinal tract, principally by intestinal bacteria, but also by digestive enzymes. A fraction of these metabolites (approximately 34% of the dose) was absorbed and subsequently excreted in the urine. At least 13 metabolites have been separated chromatographically from urine specimens. The major metabolites have been identified as 4-methylpyrogallol derivatives (i.e., sulfate, methyl, and glucuronide conjugates). One metabolite (formed by cleavage of a glucose molecule from acarbose) also has alpha-glucosidase inhibitory activity. This metabolite, together with the parent compound, recovered from the urine, accounts for less than 2% of the total administered dose.

Excretion

The fraction of acarbose that is absorbed as intact drug is almost completely excreted by the kidneys. When acarbose was given intravenously, 89% of the dose was recovered in the urine as active drug within 48 hours. In contrast, less than 2% of an oral dose was recovered in the urine as active (i.e., parent compound and active metabolite) drug. This is consistent with the low bioavailability of the parent drug. The plasma elimination half-life of acarbose activity is approximately 2 hours in healthy volunteers. Consequently, drug accumulation does not occur with three times a day (t.i.d.) oral dosing.

Special Populations

The mean steady-state area under the curve (AUC) and maximum concentrations of acarbose were approximately 1.5 times higher in elderly compared to young volunteers; however; these differences were not statistically significant. Patients with severe renal impairment (Clcr < 25 mL/min/1.73 m²) attained about 5 times higher peak plasma concentrations of acarbose and 6 times larger AUCs than volunteers with normal renal function. No studies of acarbose pharmacokinetic parameters according to race have been performed. In U.S. controlled clinical studies of acarbose in patients with type 2 diabetes mellitus, reductions in glycosylated hemoglobin levels were similar in Caucasians (N=478) and African-Americans (N=167), with a trend toward a better response in Latinos (N=132).

Drug-Drug Interactions

Studies in healthy volunteers have shown that acarbose has no effect on either the pharmacokinetics or pharmacodynamics of nifedipine, propranolol, or ranitidine. Acarbose did not interfere with the absorption or disposition of the sulfonylurea glyburide in diabetic patients. Acarbose may affect digoxin bioavailability and may require dose adjustment of digoxin by 16% (90% confidence interval: 8 to 23%), decrease mean C_max of digoxin by 26% (90% confidence interval: 16 to 34%) and decreases mean trough concentrations of digoxin by 9% (90% confidence limit: 19% decrease to 2% increase). (See PRECAUTIONS: Drug Interactions).

The amount of metformin absorbed while taking acarbose was bioequivalent to the amount absorbed when taking placebo, as indicated by the plasma AUC values. However, the peak plasma level of metformin was reduced by approximately 20% when taking acarbose due to a slight delay in the absorption of metformin. There is little if any clinically significant interaction between acarbose and metformin.

CLINICAL TRIALS

Clinical Experience from Dose Finding Studies in Type 2 Diabetes Mellitus Patients on Dietary Treatment Only

Results from six controlled, fixed-dose, monotherapy studies of acarbose in the treatment of type 2 diabetes mellitus, involving 769 acarbose-treated patients, were combined and a weighted average of the difference from placebo in the mean change from baseline in glycosylated hemoglobin (HbA1c) was calculated for each dose level as presented below:

Table 1: Mean Placebo-Subtracted Change in HbA1c in Fixed-Dose Monotherapy Studies

* Although studies utilized a maximum dose of 200 or 300 mg t.i.d., the maximum recommended dose for patients <60 kg is 50 mg t.i.d.; the maximum recommended dose for patients >60 kg is 100 mg t.i.d.
Dose of Acarbose	N	Change in HbA1c %	p-Value
25 mg t.i.d.	110	-0.44	0.0307
50 mg t.i.d.	131	-0.77	0.0001
100 mg t.i.d.	244	-0.74	0.0001
200 mg t.i.d.*	231	-0.86	0.0001
300 mg t.i.d.*	53	-1	0.0001

Results from these six fixed-dose, monotherapy studies were also combined to derive a weighted average of the difference from placebo in mean change from baseline for one-hour postprandial plasma glucose levels as shown in the following figure:

*Acarbose was statistically significantly different from placebo at all doses with respect to effect on one‑hour postprandial plasma glucose.

**The 300 mg t.i.d. acarbose regimen was superior to lower doses, but there were no statistically significant differences from 50 to 200 mg t.i.d.