Class: Antiadrenergic, peripherally acting
- Tablets 10 mg
- Tablets 25 mg
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.
T max is 1.5 to 2 h.
T 1/ 2 is about 10 h. About 85% is excreted in the urine, about 40% as unchanged drug.
Special PopulationsRenal Function Impairment
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.
Pheochromocytoma; concurrent use or use within 1 wk of MAOIs; frank CHF.
Dosage and AdministrationAdults
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.
Store at room temperature.
Drug InteractionsAlpha-blockers, beta-blockers, reserpine
Effects of guanadrel may be potentiated, resulting in excessive orthostatic hypotension and bradycardia.Indirect-acting sympathomimetics (eg, ephedrine)
Reverse antihypertensive effect.MAOIs, phenothiazines, tricyclic antidepressants
Inhibit antihypertensive effect.
Laboratory Test Interactions
None well documented.
Palpitations; chest pain; peripheral edema; orthostatic hypotension; syncope.
Fatigue; headache; faintness; drowsiness; paresthesias; confusion; depression; sleep disorders.
Dilated pupils; visual disturbances; glossitis.
Increased bowel movements; gas pain/indigestion; constipation; anorexia; nausea or vomiting; abdominal distress or pain.
Nocturia; urination urgency or frequency; ejaculation disturbances; impotence; hematuria; decreased urine output.
Shortness of breath; coughing.
Excessive weight loss or gain; aching limbs; leg cramps; back or neckache; joint pain or inflammation; gangrene.
Category B .
Safety and efficacy not established.
Drug may aggravate asthma because of depletion of catecholamines; drugs used to treat asthma may reduce hypotensive effect of guanadrel.
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.
Marked dizziness, blurred vision, syncope, orthostatic hypotension.
- 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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