Brands, Medical Use, Clinical Data
- Adrenergic alpha-Agonists
- Antihypertensive Agents
Brands / Synonyms
Estulic; Guanfacina [Inn-Spanish]; Guanfacine; Guanfacine HCl; Guanfacine Hydrochloride; Guanfacinum [Inn-Latin]; Intuniv; Tenex
For use in the management of hypertension.
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.
Rapid and complete, with an oral bioavailability of approximately 80%.
Symptoms of overdose include drowsiness, lethargy, bradycardia and hypotension. LD50=165mg/kg (orally in mice)
Biotrnasformation / Drug Metabolism
Guanfacine hydrochloride tablets are contraindicated in patients with known hypersensitivity to the drug.
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may exacerbate rebound hypertension when guanfacine is withdrawn. The beta-blocker should be withdrawn first.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.
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).
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.