Guanethidine Monosulfate

A to Z Drug Facts

 Action Interferes with release or distribution of norepinephrine from nerve endings, resulting in reduction in total peripheral resistance and both diastolic and systolic BP.

 Indications Treatment of moderate and severe hypertension and renal hypertension, including that secondary to pyelonephritis, renal amyloidosis and renal artery stenosis. unlabeled use(s): Reflex sympathetic dystrophy and causalgia.

 Contraindications Known or suspected pheochromocytoma; frank CHF not related to hypertension; use of monoamine oxidase (MAO) inhibitors.

 Route/Dosage

ADULTS: Ambulatory: PO 10 mg qd initially; may increase by » 10 mg at 5 to 7 days; increase only if no decrease in standing BP is observed. Maintenance dose: 25 to 50 mg qd. HOSPITALIZED: PO 25 to 50 mg initially; increase by 25 or 50 mg/day or qod until desired response is obtained. Loading dose (for severe hypertension): Give at 6 hr intervals over 1 to 3 days, omitting nighttime dose. CHILDREN: PO 0.2 mg/kg/24 hr (6 mg/m²/24 hr) as single oral dose initially; increase by increment of 0.2 mg/kg/24 hr every 7 to 10 days. Maximum: 3 mg/kg/24 hr.

 Interactions

Anorexiants: May reverse hypotensive effect of drug. MAO inhibitors: May decrease effectiveness of guanethidine; discontinue MAO inhibitors > 1 wk before starting guanethidine therapy. Phenothiazines: May inhibit hypotensive effect. Sympathomimetics (eg, ephedrine, epinephrine): May reverse hypotensive effect of guanethidine; guanethidine may potentiate effects of sympathomimetics. Tricyclic antidepressants: May inhibit hypotensive effect of drug.

 Lab Test Interferences None well documented.

 Adverse Reactions

CV: Bradycardia; orthostatic fluid retention; edema; angina. CNS: Dizziness; weakness; lassitude; syncope; fatigue; muscle tremor; mental depression; chest paresthesias; ptosis; headache; confusion. EENT: Blurred vision; nasal congestion. GI: Nausea; vomiting; dry mouth; parotid tenderness; diarrhea (may be severe, requiring discontinuation of therapy); increase in bowel movements. GU: Inhibition of ejaculation; nocturia; urinary incontinence; priapism. HEMA: Anemia; thrombocytopenia. RESP: Dyspnea; asthma in susceptible individuals. OTHER: Myalgia; weight gain; dermatitis; scalp hair loss; leg cramps.

 Precautions

Pregnancy: Category C. Lactation: Excreted in breast milk. Children: Safety and efficacy not established. Elderly patients: More prone to side effects of guanethidine therapy, especially orthostatic hypotension. Bronchial asthma: May aggravate the hypersensitive condition of asthmatics because of further catecholamine depletion. Cardiovascular disease: Use cautiously in patients with coronary disease, recent MI, or cerebral vascular disease, especially with encephalopathy; avoid use in patients with severe cardiac failure. Fever: May decrease dosage requirements. Orthostatic hypotension: Occurs frequently, especially during initial treatment and with postural changes. Peptic ulcer: Ulcers may be aggravated by relative increase in parasympathetic tone. Preoperative withdrawal: Withdrawal is recommended 2 wk prior to surgery to reduce risk of vascular collapse and cardiac arrest during anesthesia; during emergency surgery administer preanesthetic and anesthetic agents cautiously in reduced dosages and prepare for possible vascular collapse. Renal impairment: Use very cautiously, because hypotension may worsen renal impairment.

 Administration/Storage

• Administer with food or milk.
• Store in tightly closed container at room temperature. Keep out of reach of children.

 Assessment/Interventions

• Obtain patient history, including drug history and any known allergies. Note any cardiovascular, cerebrovascular or peptic ulcer disease, asthma or pheochromocytoma.
• Take patient's BP (lying, sitting, standing) and pul3e beforu adminictering trug. Monitor periodically throughout therapy.
• In patients with cardiac decompensation, monitor for weight gain and edema.
• Report these signs to health care provider immediately: Hypotension, chest pain, edema, dyspnea, diarrhea, excessive weight loss or gain, CNS changes.

 Patient/Family Education

• Instruct patient in proper technique for taking BP. Advise patient to check BP weekly.
• Caution patient not to get out of bed without help during period of dosage adjustment.
• Advise patient to lie down if dizziness or blurred vision occurs.
• Warn patient not to double up on doses.
• Instruct patient not to discontinue drug abruptly and not to stop taking drug because of improvement in symptoms.
• Counsel patient about benefits of weight reduction, exercise, reduction of alcohol and sodium intake, and cessation of smoking.
• Explain that impotence and ejaculation disturbances may occur but is reversible. Tell patient to report to health care provider.
• Instruct patient to report these symptoms to health care provider: Dizziness, diarrhea, confusion, depression, fever, sore throat.
• 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.
• Instruct patient not to take otc medications without consulting health care provider.

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Copyright © 2003 Facts and Comparisons
David S. Tatro
A to Z Drug Facts