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Pronunciation:

(GWAHN a benz)

Synonyms:

Guanabenz Acetate

Generic Available:

Yes

Canadian Brand Names:

Wytensin®

Use:

Management of hypertension

Pregnancy Risk Factor:

Contraindications:

Hypersensitivity to guanabenz or any component of the formulation

Warnings/Precautions:

Use with caution in severe hepatic or renal failure. Avoid in pregnancy and breast-feeding. Safety and efficacy for use in children <12 years of age have not been demonstrated. Use with caution in patients with severe coronary insufficiency, recent MI or cerebrovascular disease. Abrupt discontinuation can result in rebound hypertension. Avoid use in CNS disease, elderly or with other CNS depressants (can cause sedation and drowsiness alone). May cause significant orthostasis.

Adverse Reactions:

Higher rates with larger doses

>5% (at doses of 16 mg/day):

Cardiovascular: Orthostasis

Central nervous system: Drowsiness or sedation (39%), dizziness (12% to 17%), headache (5%)

Gastrointestinal: Xerostomia (28% to 38%)

Neuromuscular & skeletal: Weakness (~10%)

3% (may be similar to placebo):

Cardiovascular: Arrhythmias, palpitation, chest pain, edema

Central nervous system: Anxiety, ataxia, depression, sleep disturbances

Dermatologic: Rash, pruritus

Endocrine & metabolic: Disturbances of sexual function, gynecomastia, decreased sexual function

Gastrointestinal: Diarrhea, vomiting, constipation, nausea

Genitourinary: Polyuria

Neuromuscular & skeletal: Myalgia

Ocular: Blurring of vision

Respiratory: Nasal congestion, dyspnea

Miscellaneous: Taste disorders

Drug Interactions:

Substrate of CYP1A2 (major)

CYP1A2 inducers: May decrease the levels/effects of guanabenz. Example inducers include aminoglutethimide, carbamazepine, phenobarbital, and rifampin.

CYP1A2 inhibitors: May increase the levels/effects of guanabenz. Example inhibitors include amiodarone, ciprofloxacin, fluvoxamine, ketoconazole, norfloxacin, ofloxacin, and rofecoxib.

Hypoglycemic symptoms may be reduced. Educate patient about decreased signs and symptoms of hypoglycemia or avoid use in patients with frequent episodes of hypoglycemia.

Nitroprusside and guanabenz have additive hypotensive effects.

Noncardioselective beta-blockers (nadolol, propranolol, timolol) may exacerbate rebound hypertension when guanabenz is withdrawn. The beta-blocker should be withdrawn first. The gradual withdrawal of guanabenz or a cardioselective beta-blocker could be substituted.

TCAs decrease the hypotensive effect of guanabenz.

Stability:

Protect from light.

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: Antihypertensive: ~1 hour

Absorption: ~75%

Half-life elimination, serum: 7-10 hours

Dosage:

Adults: Oral: Initial: 4 mg twice daily; increase in increments of 4-8 mg/day every 1-2 weeks to a maximum of 32 mg twice daily.

Dosing adjustment in hepatic impairment: Probably necessary

Monitoring Parameters:

Monitor blood pressure, standing and sitting/supine

Patient Education:

May impair alertness, judgment, coordination; do not abruptly discontinue; do not discontinue without notifying physician

Additional Information:

Considered an alternate to clonidine; it causes less sodium retention than clonidine or methyldopa.

Anesthesia and Critical Care Concerns/Other Considerations:

Guanabenz is not routinely used in clinical practice because of significant and marked orthostatic hypotension.

Cardiovascular Considerations:

Not routinely used in clinical practice because of significant and marked orthostatic hypotension.

Dental Health: Effects on Dental Treatment:

Key adverse event(s) related to dental treatment: Taste disorder, nasal congestion, dyspnea, significant xerostomia (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 and dizziness are common; may cause anxiety 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 guanabenz

Dosage Forms:

Tablet: 4 mg, 8 mg

International Brand Names:

Lisapres® (BR); Wytensin® (CA)

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.

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