Guanfacine Hydrochloride
Pronunciation: (GWAHN-fay-seen HIGH-droe-KLOR-ide)Class: Antiadrenergic, centrally acting
Trade Names:
Tenex
- Tablets 1 mg
- Tablets 2 mg
Pharmacology
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Appears to stimulate central alpha 2 -adrenergic receptors, with decreased sympathetic outflow causing decrease in peripheral vascular resistance and reduction in heart rate.
Pharmacokinetics
Absorption
Absolute bioavailability is about 80%. T max is 1 to 4 h.
Distribution
Protein binding is about 70%. Mean Vd is 6.3 L/kg.
Elimination
T 1/ 2 is 10 to 30 h. About 50% is excreted in the urine as unchanged, the remainder as metabolites.
Special Populations
Renal Function ImpairmentCl is reduced; plasma levels are only slightly increased.
Indications and Usage
Treatment of hypertension.
Unlabeled Uses
Amelioration of heroin withdrawal symptoms.
Contraindications
Standard considerations.
Dosage and Administration
AdultsPO 1 mg daily at bedtime; may increase gradually up to 3 mg daily.
General Advice
Administer medication at bedtime to decrease daytime sedation.
Storage/Stability
Store in tightly closed container and protect from light.
Drug Interactions
Alcohol, CNS depressantsIncreased CNS depression.
Barbiturates, phenytoinDecreased guanfacine levels with loss of antihypertensive effect.
Laboratory Test Interactions
None well documented.
Adverse Reactions
Cardiovascular
Chest pain; bradycardia; palpitations.
CNS
Somnolence; drowsiness; dizziness; headache; sleep disturbances; insomnia; confusion; depression.
Dermatologic
Dermatitis; pruritus; sweating.
EENT
Conjunctivitis; visual disturbance; tinnitus; rhinitis; taste perversion.
GI
Dry mouth; constipation; diarrhea; nausea; abdominal discomfort; dyspnea.
Genitourinary
Urinary incontinence; testicular disorder; decreased libido; impotence.
Miscellaneous
Paresthesia; paresis; leg cramps; hypokinesia.
Precautions
Pregnancy
Category B .
Lactation
Excreted in breast milk.
Children
Safety and efficacy in children younger than 12 yr of age not established.
Special Risk Patients
Use with caution in patients with severe coronary insufficiency, recent MI, cerebrovascular disease, or chronic renal or hepatic function impairment.
Sedation
Occurs in a large percentage of patients.
Withdrawal
Do not discontinue therapy without consulting health care provider; drug must be withdrawn gradually to avoid rapid rise in BP (rebound hypertension).
Overdosage
Symptoms
Severe drowsiness, hypotension, bradycardia.
Patient Information
- Instruct patient to take medication at bedtime.
- Teach patient proper technique for taking BP. Advise patient to check BP weekly.
- Instruct patient not to discontinue drug abruptly.
- Advise patient on benefits of weight loss, exercise, reduction of alcohol and sodium intake and cessation of smoking.
- Instruct patient to lie down if dizziness or blurred vision occurs.
- Explain that impotence may occur but is reversible. Tell patient to report to health care provider.
- Instruct patient to report these symptoms to health care provider: dizziness, constipation, headache, insomnia, nausea, sweating, or weakness.
- Advise patient to take sips of water frequently, suck on ice chips or sugarless hard candy, or chew sugarless gum if dry mouth occurs.
- Caution patient to avoid sudden position changes to avoid orthostatic hypotension.
- Instruct patient to avoid intake of alcoholic beverages or other CNS depressants.
- Advise patient that drug may cause drowsiness and to use caution while driving or performing other tasks requiring mental alertness.
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High Blood Pressure, Attention Deficit Hyperactivity Disorder
