Overview
DESCRIPTION Guanfacine hydrochloride, USP is a centrally acting antihypertensive with α 2 -adrenoceptor agonist properties in tablet form for oral administration. The chemical name of guanfacine hydrochloride, USP is N -Amidino- 2-(2,6-dichlorophenyl) acetamide monohydrochloride and its molecular weight is 282.55.
Mechanism of Action
CLINICAL PHARMACOLOGY Guanfacine hydrochloride is an orally active antihypertensive agent whose principal mechanism of action appears to be stimulation of central α 2 -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.
Indications
- INDICATIONS AND USAGE Guanfacine tablets, USP are indicated in the management of hypertension. Guanfacine tablets, USP may be given alone or in combination with other antihypertensive agents, especially thiazide-type diuretics.
Common Doses
- 1 mg
- 2 mg
- 3 mg
Dosage
DOSAGE AND ADMINISTRATION The recommended initial dose of guanfacine tablets when given alone or in combination with another antihypertensive drug is 1 mg daily given at bedtime to minimize somnolence. If after 3 weeks to 4 weeks of therapy 1 mg does not give a satisfactory result, a dose of 2 mg may be given, although most of the effect of guanfacine tablets are seen at 1 mg (see CLINICAL PHARMACOLOGY ). Higher daily doses have been used, but adverse reactions increase significantly with doses above 3 mg/day. The frequency of rebound hypertension is low, but it can occur.
Contraindications
- CONTRAINDICATIONS Guanfacine tablets are contraindicated in patients with known hypersensitivity to guanfacine hydrochloride.
Side Effects
- ADVERSE REACTIONS Adverse reactions noted with guanfacine hydrochloride are similar to those of other drugs of the central α 2 -adrenoreceptor agonist class: dry mouth, sedation (somnolence), weakness (asthenia), dizziness, constipation, and impotence. While the reactions are common, most are mild and tend to disappear on continued dosing. Skin rash with exfoliation has been reported in a few cases; although clear cause and effect relationships to guanfacine tablets could not be established, should a rash occur, guanfacine tablets should be discontinued and the patient monitored appropriately.
Interactions
- No major interactions listed on the FDA label. Always consult a healthcare professional.