Guanfacine

GUANFACINE- guanfacine hydrochloride tablet
Mylan Pharmaceuticals Inc.

DESCRIPTION

Guanfacine tablets are a centrally acting antihypertensive with α2 -adrenoceptor agonist properties in tablet form for oral administration.

The chemical name of guanfacine hydrochloride is N-Amidino-2-(2,6-dichlorophenyl) acetamide monohydrochloride and its molecular weight is 282.55. Its structural formula is:

Guanfacine Hydrochloride Structural Formula

Guanfacine hydrochloride, USP is a white to off-white crystalline powder; sparingly soluble in water and alcohol and slightly soluble in acetone.

Each tablet, for oral administration, contains guanfacine hydrochloride equivalent to 1 mg or 2 mg of guanfacine and the following inactive ingredients: anhydrous lactose, colloidal silicon dioxide, magnesium stearate, microcrystalline cellulose and sodium lauryl sulfate. In addition, the 2 mg tablets contain the following ingredient: FD&C Blue No.1 Aluminum Lake.

CLINICAL PHARMACOLOGY

Guanfacine tablets are an orally active antihypertensive agent whose principal mechanism of action appears to be stimulation of central α2 -adrenergic receptors. By stimulating these receptors, guanfacine reduces sympathetic nerve impulses from the vasomotor center to the heart and blood vessels. This results in a decrease in peripheral vascular resistance and a reduction in heart rate.

The dose-response relationship for blood pressure and adverse effects of guanfacine given once a day as monotherapy has been evaluated in patients with mild to moderate hypertension. In this study patients were randomized to placebo or to 0.5 mg, 1 mg, 2 mg, 3 mg or 5 mg of guanfacine tablets. Results are shown in the following table. A useful effect was not observed overall until doses of 2 mg were reached, although responses in white patients were seen at 1 mg; 24 hour effectiveness of 1 mg to 3 mg doses was documented using 24 hour ambulatory monitoring. While the 5 mg dose added an increment of effectiveness, it caused an unacceptable increase in adverse reactions.

Mean Changes (mm Hg) from Baseline in Seated Systolic and Diastolic Blood Pressure for Patients Completing 4 to 8 Weeks of Treatment with Guanfacine Monotherapy
Mean Change S/D * Seated n = (range) Placebo 0.5 mg 1 mg 2 mg 3 mg 5 mg
*
S/D = Systolic/diastolic blood pressure

White Patients

11 to 30

-1/-5

-6/-8

-8/-9

-12/-11

-15/-12

-18/-16

Black Patients

8 to 28

-3/-5

0/-2

-3/-5

-7/-7

-8/-9

-19/-15

Controlled clinical trials in patients with mild to moderate hypertension who were receiving a thiazide-type diuretic have defined the dose-response relationship for blood pressure response and adverse reactions of guanfacine given at bedtime and have shown that the blood pressure response to guanfacine can persist for 24 hours after a single dose. In the 12-week, placebo-controlled dose-response study, patients were randomized to placebo or to doses of 0.5 mg, 1 mg, 2 mg and 3 mg of guanfacine, in addition to 25 mg chlorthalidone, each given at bedtime. The observed mean changes from baseline, tabulated below, indicate the similarity of response for placebo and the 0.5 mg dose. Doses of 1 mg, 2 mg and 3 mg resulted in decreased blood pressure in the sitting position with no real differences among the three doses. In the standing position, there was some increase in response with dose.

Mean Decreases (mm Hg) in Seated and Standing Blood Pressure for Patients Treated with Guanfacine in Combination with Chlorthalidone
Mean Change n = Placebo 63 0.5 mg 63 1 mg 64 2 mg 58 3 mg 59
*
S/D = Systolic/diastolic blood pressure

SD * Seated

-5/-7

-5/-6

-14/-13

-12/-13

-16/-13

SD * Standing

-3/-5

-5/-4

-11/-9

-9/-10

-15/-12

While most of the effectiveness of guanfacine in combination (and as monotherapy in white patients) was present at 1 mg, adverse reactions at this dose were not clearly distinguishable from those associated with placebo. Adverse reactions were clearly present at 2 mg and 3 mg (see ADVERSE REACTIONS).

In a second 12-week placebo-controlled study of 1 mg, 2 mg or 3 mg of guanfacine tablets administered with 25 mg of chlorthalidone once daily, a significant decrease in blood pressure was maintained for a full 24 hours after dosing. While there was no significant difference between the 12 and 24 hour blood pressure readings, the fall in blood pressure at 24 hours was numerically smaller, suggesting possible escape of blood pressure in some patients and the need for individualization of therapy.

In a double-blind, randomized trial, either guanfacine or clonidine was given at recommended doses with 25 mg chlorthalidone for 24 weeks and then abruptly discontinued. Results showed equal degrees of blood pressure reduction with the two drugs and there was no tendency for blood pressures to increase despite maintenance of the same daily dose of the two drugs. Signs and symptoms of rebound phenomena were infrequent upon discontinuation of either drug. Abrupt withdrawal of clonidine produced a rapid return of diastolic and especially systolic blood pressure to approximately pretreatment levels, with occasional values significantly greater than baseline, whereas guanfacine withdrawal produced a more gradual increase to pretreatment levels, but also with occasional values significantly greater than baseline.

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