Active ingredient: Guanfacine - Brands, Medical Use, Clinical Data

Brands, Medical Use, Clinical Data

Drug Category

• Adrenergic alpha-Agonists
• Sympatholytics
• Antihypertensive Agents

Dosage Forms

• Tablet (oral)

Brands / Synonyms

Estulic; Guanfacina [Inn-Spanish]; Guanfacine; Guanfacine HCl; Guanfacine Hydrochloride; Guanfacinum [Inn-Latin]; Intuniv; Tenex

Indications

For use in the management of hypertension.

Pharmacology

Similar to clonidine, guanfacine is a centrally-acting, alpha(2)-adrenergic receptor agonist used alone or in combination with other drugs for the treatment of hypertension.

Mechanism of Action

Guanfacine selectively stimulates central alpha(2)-adrenergic receptors, resulting in inhibition of sympathetic nervous system outflow, reduction of peripheral and renal vascular resistance, and lowering of blood pressure and heart rate.

Absorption

Rapid and complete, with an oral bioavailability of approximately 80%.

Toxicity

Symptoms of overdose include drowsiness, lethargy, bradycardia and hypotension. LD₅₀=165mg/kg (orally in mice)

Biotrnasformation / Drug Metabolism

Hepatic

Contraindications

Guanfacine hydrochloride tablets are contraindicated in patients with known hypersensitivity to the drug.

Drug Interactions

The potential for increased sedation when guanfacine is given with other CNS-depressant drug should be appreciated. The administration of guanfacine concomitantly with known microsomal enzyme inducer (phenobarbital or phenytoin) to two patients with renal impairment reportedly resulted in significant reductions in elimination half-life and plasma concentration. In such cases, therefore, more frequent dosing may be required to achieve or maintain the desired hypotensive response. Further, if guanfacine is to be discontinued in such patients, careful tapering of the dosage may be necessary in order to avoid rebound phenomena.

TCAs decrease the hypotensive effect of guanfacine. Noncardioselective beta-blockers (nadolol,porpranolol,timolol) may exacerbate rebound hypertension when guanfacine is withdrawn. The beta-blocker should be withdrawn first. The gradual withdrawal of guafacine or a cardioselective beta-blocker could be substituted.

Anticoagulants

Ten patients who were stabilized on oral anticoagulants were given guanfacine, 1-2 mg/day, for 4 weeks. No changes were observed in the degree of anticoagulation. In several well-controlled studies, guanfacine was administered together with diuretics with no drug interactions reported. In the long-term safety studies, guanfacine was given concomitantly with many drugs without evidence of any interactions. The principal drugs given (number of patients in parentheses) were: cardiac glycosides (115), sedatives and hypnotics (103), coronary vasodilators (52), oral hypoglycemics (45), cough and cold preparations (45), NSAIDs (38), antihyperlipidemics (29), antigout drugs (24), oral contraceptives (18), bronchodilators (13), insulin (10), and beta blockers (10).

Laboratory Test

In clinical trials, no clinically relevant laboratory test abnormalities were identified as causally related to drug during short-term treatment with guanfacine.

Drug/Laboratory Test Interactions

No laboratory test abnormalities related to the use of guanfacine have been identified.