Guanfacine
Pronunciation
(GWAHN fa seen)
U.S. Brand Names
Tenex®
Synonyms
Guanfacine Hydrochloride
Generic Available
Yes
Canadian Brand Names
Tenex®
Use
Management of hypertension
Pregnancy Risk Factor
B
Contraindications
Hypersensitivity to guanfacine or any component of the formulation
Warnings/Precautions
Use caution with severe coronary insufficiency, recent MI, cerebrovascular disease, or chronic renal or hepatic disease. Abrupt discontinuation can result in nervousness, anxiety and rarely, rebound hypertension (occurs 2-4 days after withdrawal). Avoid use in CNS disease, elderly, or with other CNS depressants (can cause sedation and drowsiness alone). Caution in diabetes; may mask signs of hypoglycemia. Safety and efficacy in children <12 years of age have not been demonstrated. May cause orthostasis.
Adverse Reactions
>10%:
Central nervous system: Somnolence (5% to 40%), headache (3% to 13%), dizziness (2% to 15%)
Gastrointestinal: Xerostomia (10% to 54%), constipation (2% to 15%)
1% to 10%:
Central nervous system: Fatigue (2% to 10%)
Endocrine & metabolic: Impotence (up to 7%)
<1% (Limited to important or life-threatening): Agitation, alopecia, amnesia, blurred vision, bradycardia, chest pain, confusion, depression, dermatitis, diaphoresis, dysphagia, dyspnea, edema, exfoliative dermatitis, hypokinesia, hypotension, insomnia, leg cramps, malaise, nervousness, orthostasis, palpitation, paresthesia, pruritus, rash, rebound hypertension, syncope, tinnitus, urinary incontinence, vertigo; Note: Mania and aggressive behavior have been reported in pediatric patients with ADHD who received guanfacine.
Drug Interactions
Nitroprusside and guanfacine have additive hypotensive effects.
Noncardioselective beta-blockers (nadolol, propranolol, timolol) may exacerbate rebound hypertension when guanfacine is withdrawn. The beta-blocker should be withdrawn first. The gradual withdrawal of guanfacine or a cardioselective beta-blocker could be substituted.
TCAs decrease the hypotensive effect of guanfacine.
Mechanism of Action
Stimulates alpha2-adrenoreceptors in the brain stem, thus activating an inhibitory neuron, resulting in reduced sympathetic outflow, producing a decrease in vasomotor tone and heart rate
Pharmacodynamics/Kinetics
Onset of action: Peak effect: 8-11 hours
Duration: 24 hours following single dose
Half-life elimination, serum: 17 hours
Time to peak, serum: 1-4 hours
Dosage
Adults: Oral: Hypertension: 1 mg usually at bedtime, may increase if needed at 3- to 4-week intervals; usual dose range (JNC 7): 0.5-2 mg once daily
Patient Education
May impair alertness, judgment, coordination; do not abruptly discontinue; do not discontinue without notifying physician
Nursing Implications
Monitor blood pressure, standing and sitting/supine; observe for orthostasis
Additional Information
More selective alpha2 agonist than clonidine; withdrawal effects rarely occur due to its long half-life.
Anesthesia and Critical Care Concerns/Other Considerations
Guanfacine is not routinely used in clinical practice because of significant and marked hypotension.
Cardiovascular Considerations
Not routinely used in clinical practice because of significant and marked hypotension.
Dental Health: Effects on Dental Treatment
Key adverse event(s) related to dental treatment: Xerostomia and changes in salivation (normal salivary flow resumes upon discontinuation).
Dental Health: Vasoconstrictor/Local Anesthetic Precautions
No information available to require special precautions
Mental Health: Effects on Mental Status
Drowsiness is common; may cause insomnia or dizziness, may rarely cause confusion or depression
Mental Health: Effects on Psychiatric Treatment
Has been used to treat ADHD; concurrent use with psychotropics may produce additive sedation and dry mouth; TCAs may decrease the hypotensive effect of guanfacine
Dosage Forms
Tablet: 1 mg, 2 mg
References
Chobanian AV, Bakris GL, Black HR, et al, "The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure: The JNC 7 Report,"JAMA, 2003, 289(19):2560-71.
"Consensus Recommendations for the Management of Chronic Heart Failure. On Behalf of the Membership of the Advisory Council to Improve Outcomes Nationwide in Heart Failure,"Am J Cardiol, 1999, 83(2A):1A-38A.
Kaplan NM and Sever PS, "Combination Therapy: A Key to Comprehensive Patient Care,"Am J Hypertens, 1997, 10(7 Pt 2):127S.
Moser M and Black HR, "The Role of Combination Therapy in the Treatment of Hypertension,"Am J Hypertens, 1998, 11(6 Pt 2):73S-8S, 95S-100S.
International Brand Names
Estulic® (BE, CZ, FR, HU, MT, NL, PL, RO); Estulik® (RU); Tenex® (CA)