Guanadrel

Pronunciation: GWAHN-uh-drell
Class: Antiadrenergic, peripherally acting

Trade Names:
Hylorel
- Tablets 10 mg
- Tablets 25 mg

Pharmacology

Inhibits vasoconstriction by restraining norepinephrine release from nerve storage sites; depletion of norepinephrine causes relaxation of vascular smooth muscle, decreasing total peripheral resistance, and venous return.

Pharmacokinetics

Absorption

T _max is 1.5 to 2 h.

Elimination

T _{1/ 2} is about 10 h. About 85% is excreted in the urine, about 40% as unchanged drug.

Special Populations

Total Cl decreases and t _{1/ 2} is prolonged. Dosage adjustment may be necessary.

Indications and Usage

Treatment of hypertension in patients not responding adequately to thiazide-type diuretics.

Contraindications

Pheochromocytoma; concurrent use or use within 1 wk of MAOIs; frank CHF.

Dosage and Administration

PO 10 mg/day (5 mg twice daily) initially. Maintenance dose: PO 20 to 75 mg/day, usually in 2 divided doses; 3 or 4 times daily dosing may be needed. In patients with renal function impairment, dosage adjustment may be necessary.

Storage/Stability

Store at room temperature.

Drug Interactions

Effects of guanadrel may be potentiated, resulting in excessive orthostatic hypotension and bradycardia.

Reverse antihypertensive effect.

Inhibit antihypertensive effect.

Laboratory Test Interactions

None well documented.

Adverse Reactions

Cardiovascular

Palpitations; chest pain; peripheral edema; orthostatic hypotension; syncope.

CNS

Fatigue; headache; faintness; drowsiness; paresthesias; confusion; depression; sleep disorders.

EENT

Dilated pupils; visual disturbances; glossitis.

GI

Increased bowel movements; gas pain/indigestion; constipation; anorexia; nausea or vomiting; abdominal distress or pain.

Genitourinary

Nocturia; urination urgency or frequency; ejaculation disturbances; impotence; hematuria; decreased urine output.

Respiratory

Shortness of breath; coughing.

Miscellaneous

Excessive weight loss or gain; aching limbs; leg cramps; back or neckache; joint pain or inflammation; gangrene.

Precautions

Pregnancy

Category B .

Lactation

Undetermined.

Children

Safety and efficacy not established.

Asthma

Drug may aggravate asthma because of depletion of catecholamines; drugs used to treat asthma may reduce hypotensive effect of guanadrel.

Surgery

Discontinue 48 to 72 h before elective surgery to prevent vascular collapse during anesthesia; for emergency surgery, preanesthetic and anesthetic agents are administered in reduced dosage.

Overdosage

Symptoms

Marked dizziness, blurred vision, syncope, orthostatic hypotension.

Patient Information

• Teach proper technique for taking BP. Advise patient to check BP weekly.
• Instruct patient not to discontinue drug abruptly.
• Advise patient about benefits of weight reduction, exercise, reduction of alcohol and sodium intake, cessation of smoking.
• Tell patient to lie down if dizziness or blurred vision occurs.
• Explain that impotence or ejaculation disturbance may occur but is reversible. Tell patient to report to health care provider.
• Instruct patient to report these symptoms to health care provider: headache, dizziness, myalgia, depression, chest pain, nausea, visual disturbances.
• Caution patient to avoid sudden position changes to prevent orthostatic hypotension.
• Caution 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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