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, PRECOSE 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, PRECOSE 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
PRECOSE to enhance glycemic control is additive to that of sulfonylureas,
insulin or metformin when used in combination. In addition, PRECOSE 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 14C-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 14C-labeled acarbose, peak plasma concentrations of
radioactivity were attained 14–24 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 (that
is, 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
(that is, 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/1.73m²)
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 PRECOSE 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 PRECOSE has no
effect on either the pharmacokinetics or pharmacodynamics of nifedipine,
propranolol, or ranitidine. PRECOSE did not interfere with the absorption or
disposition of the sulfonylurea glyburide in diabetic patients. PRECOSE may
affect digoxin bioavailability and may require dose adjustment of digoxin by
16% (90% confidence interval: 8-23%), decrease mean Cmax of digoxin by 26% (90%
confidence interval: 16–34%) 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 PRECOSE 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 PRECOSE due to a slight delay in the absorption
of metformin. There is little if any clinically significant interaction between
PRECOSE 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 PRECOSE in the treatment of type 2 diabetes mellitus, involving 769
PRECOSE-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 |
Dose of PRECOSE* |
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 |
* PRECOSE was statistically
significantly different from placebo at all doses. Although there were no
statistically significant differences among the mean results for doses ranging
from 50 to 300 mg t.i.d., some patients may derive benefit by increasing the dosage
from 50 to 100 mg t.i.d. |
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.
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:
Figure 1
* PRECOSE 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. PRECOSE
regimen was superior to lower doses, but there were no statistically
significant differences from 50 to 200 mg t.i.d.
Clinical Experience in Type 2
Diabetes Mellitus Patients on Monotherapy, or in Combination with
Sulfonylureas, Metformin or Insulin
PRECOSE was studied as monotherapy
and as combination therapy to sulfonylurea, metformin, or insulin treatment.
The treatment effects on HbA1c levels and one-hour postprandial glucose levels
are summarized for four placebo-controlled, double-blind, randomized studies
conducted in the United States in Tables 2 and 3, respectively. The
placebo-subtracted treatment differences, which are summarized below, were
statistically significant for both variables in all of these studies.
Study 1 (n=109) involved patients
on background treatment with diet only. The mean effect of the addition of
PRECOSE to diet therapy was a change in HbA1c of -0.78%, and an improvement of
one-hour postprandial glucose of -74.4 mg/dL.
In Study 2 (n=137), the mean
effect of the addition of PRECOSE to maximum sulfonylurea therapy was a change
in HbA1c of -0.54%, and an improvement of one-hour postprandial glucose of
-33.5 mg/dL.
In Study 3 (n=147), the mean
effect of the addition of PRECOSE to maximum metformin therapy was a change in
HbA1c of -0.65%, and an improvement of one-hour postprandial glucose of -34.3
mg/dL.
Study 4 (n=145) demonstrated that
PRECOSE added to patients on background treatment with insulin resulted in a
mean change in HbA1c of -0.69%, and an improvement of one-hour postprandial
glucose of -36.0 mg/dL.
A one year study of PRECOSE as
monotherapy or in combination with sulfonylurea, metformin or insulin treatment
was conducted in Canada in which 316 patients were included in the primary
efficacy analysis (Figure 2). In the diet, sulfonylurea and metformin groups,
the mean decrease in HbA1c produced by the addition of PRECOSE was
statistically significant at six months, and this effect was persistent at one
year. In the PRECOSE-treated patients on insulin, there was a statistically
significant reduction in HbA1c at six months, and a trend for a reduction at
one year.
Table 2: Effect of Precose on HbA1c
Study |
Treatment |
HbA1c (%)a |
p-Value |
Mean Baseline |
Mean change from baselineb |
Treatment Difference |
1 |
Placebo Plus Diet |
8.67 |
0.33 |
— |
— |
PRECOSE 100 mg t.i.d. Plus Diet |
8.69 |
-0.45 |
-0.78 |
0.0001 |
2 |
Placebo Plus SFUc |
9.56 |
0.24 |
— |
— |
PRECOSE 50–300d mg t.i.d. Plus SFUc |
9.64 |
-0.3 |
-0.54 |
0.0096 |
3 |
Placebo Plus Metformine |
8.17 |
+0.08 g |
— |
— |
PRECOSE 50–100 mg t.i.d. Plus Metformine |
8.46 |
-0.57 g |
-0.65 |
0.0001 |
4 |
Placebo Plus Insulinf |
8.69 |
0.11 |
— |
— |
PRECOSE 50–100 mg t.i.d. Plus Insulinf |
8.77 |
-0.58 |
-0.69 |
0.0001 |
aHbA1c Normal Range: 4–6%
bAfter four months treatment in Study 1, and six months in Studies
2, 3, and 4
cSFU, sulfonylurea, maximum dose
dAlthough studies utilized a maximum dose of up to 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.
eMetformin
dosed at 2000 mg/day or 2500 mg/day
fMean dose of insulin 61 U/day
gResults are adjusted to a common baseline of 8.33% |
Table 3: Effect of Precose on Postprandial Glucose
Study |
Treatment |
One-Hour Postprandial Glucose (mg/dL) |
p-Value |
Mean Baseline |
Mean change from baselinea |
Treatment Difference |
1 |
Placebo Plus Diet |
297.1 |
31.8 |
— |
— |
PRECOSE 100 mg t.i.d. Plus Diet |
299.1 |
-42.6 |
-74.4 |
0.0001 |
2 |
Placebo Plus SFUb |
308.6 |
6.2 |
— |
— |
PRECOSE 50–300c mg t.i.d. Plus SFUb |
311.1 |
-27.3 |
-33.5 |
0.0017 |
3 |
Placebo Plus Metformind |
263.9 |
+3.3f |
— |
— |
PRECOSE 50–100 mg t.i.d. Plus Metformind |
283 |
-31.0f |
-34.3 |
0.0001 |
4 |
Placebo Plus Insuline |
279.2 |
8 |
— |
— |
PRECOSE 50–100 mg t.i.d. Plus Insuline |
277.8 |
-28 |
-36 |
0.0178 |
aAfter four months treatment in Study 1, and six months in
Studies 2, 3, and 4
bSFU, sulfonylurea, maximum dose
cAlthough studies utilized a maximum dose of up to 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.
dMetformin
dosed at 2000 mg/day or 2500 mg/day
eMean dose of insulin 61 U/day
fResults are adjusted to a common baseline of 273 mg/dL |
Figure 2
Figure 2: Effects of PRECOSE (III ) and Placebo ( III ) on mean change in HbA1c levels from baseline
throughout a one-year study in patients with type 2 diabetes mellitus when used
in combination with: (A) diet alone; (B) sulfonylurea; (C) metformin; or (D)
insulin. Treatment differences at 6 and 12 months were tested: * p < 0.01; #
p = 0.077.