DrugindexOnline^{2nd edition}

Pronouncation: (GWAHN-uh-benz ASS-uh-TATE)
Class: Antiadrenergic, centrally acting

Trade Names:
Wytensin
- Tablets 4 mg
- Tablets 8 mg

Mechanism of Action

Pharmacology

Appears to stimulate central alpha ₂ -adrenergic receptors, inhibiting sympathetic outflow from brain to peripheral circulation.

Pharmacokinetics

Absorption

Bioavailability is about 75%.

Elimination

Less than 1% is excreted in the urine unchanged.

Onset

60 min.

Peak

2 to 4 h.

Duration

6 to 8 h.

Indications and Usage

Treatment of hypertension alone or with a thiazide diuretic.

Contraindications

Standard considerations.

Dosage and Administration

Adults

PO 4 mg twice daily initially; may increase by 4 to 8 mg daily every 1 to 2 wk; max dose 32 mg twice daily.

Storage/Stability

Store in tightly closed container in cool environment.

Drug Interactions

CNS depressants

Increased sedation.

Laboratory Test Interactions

None well documented.

Adverse Reactions

Cardiovascular

Chest pain; edema; arrhythmias; palpitations; atrioventricular dysfunction.

CNS

Drowsiness; sedation; dizziness; anxiety; ataxia; depression; sleep disturbances.

Dermatologic

Rash; pruritus.

EENT

Blurred vision; nasal congestion.

GI

Dry mouth; constipation; diarrhea; nausea; vomiting; abdominal discomfort.

Genitourinary

Urinary frequency; disturbances of sexual function.

Hepatic

Increased liver enzymes.

Respiratory

Dyspnea.

Miscellaneous

Gynecomastia; muscle or joint pain; weakness; taste disorders.

Precautions

Monitor BP Monitor BP carefully in patients with coexisting hypertension and chronic hepatic dysfunction or renal impairment.

Pregnancy

Category C .

Lactation

Undetermined.

Children

Safety and efficacy in children younger than 12 yr not established.

Special Risk Patients

Use with caution in patients with severe coronary insufficiency, recent MI, or cerebrovascular disease.

Sedation

Occurs in 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Do not discontinue therapy without consulting health care provider; drug must be withdrawn gradually to avoid rapid rise in BP.

Overdosage

Symptoms

Marked hypotension, somnolence, lethargy, irritability, miosis, bradycardia.

Patient Information

• Instruct patient and family member in proper technique for taking BP. Advise patient to check and record BP weekly.
• Advise 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 not to discontinue drug abruptly.
• Counsel patient about benefits of weight reduction, exercise, reduction of alcohol and sodium, cessation of smoking.
• Instruct patient to report these symptoms to health care provider: headache, dizziness, weakness, blurred vision.
• 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 prevent 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.