Home Drug Guide Guanethidine Monosulfate

Drug Guide

Generic Name

Guanethidine Monosulfate

Brand Names Ismelin

Classification

Therapeutic: Antihypertensive; Sympatholytic agent

Pharmacological: Adrenergic neuron blokcer

FDA Approved Indications

Hypertension (primarily used in the past)

Mechanism of Action

Guanethidine inhibits the release of norepinephrine from sympathetic nerve endings, leading to vasodilation and decreased blood pressure.

Dosage and Administration

Adult: Initially, 20-50 mg daily in divided doses; dosage adjusted based on response and tolerability.

Pediatric: Not typically used in pediatric populations.

Geriatric: Start at lower doses; monitor closely for side effects.

Renal Impairment: Adjust dose as needed; renal function monitoring recommended.

Hepatic Impairment: No specific guidelines; use with caution.

Pharmacokinetics

Absorption: Moderate; 40-60% bioavailability after oral administration.

Distribution: Widely distributed; crosses the blood-brain barrier.

Metabolism: Minimal hepatic metabolism.

Excretion: Primarily renal excretion.

Half Life: Approximately 10-12 hours.

Contraindications

Known hypersensitivity to guanethidine
Severe cardiovascular disease

Precautions

Use with caution in patients with renal impairment, cerebrovascular disease, or bipolar disorder; may cause or exacerbate depression, orthostatic hypotension, and urinary retention.

Adverse Reactions - Common

Orthostatic hypotension (Frequent)
Diarrhea (Common)
Nasal congestion (Common)

Adverse Reactions - Serious

Severe hypotension (Rare)
Peripheral neuropathy with long-term use (Rare)
Psychiatric disturbances, depression (Rare)

Drug-Drug Interactions

Antihypertensive agents, especially other vasodilators or centrally acting agents.
MAO inhibitors may potentiate hypotensive effects.

Drug-Food Interactions

N/A

Drug-Herb Interactions

N/A

Nursing Implications

Assessment: Monitor blood pressure, heart rate, mental status, and urinary output.

Diagnoses:

Risk for falls due to hypotension.
Impaired cardiac perfusion.

Implementation: Administer as prescribed; monitor for signs of hypotension and adverse effects.

Evaluation: Assess blood pressure response and symptom control; adjust dose accordingly.

Patient/Family Teaching

Rise slowly from sitting or lying position to minimize dizziness.
Report signs of depression, urinary retention, or severe hypotension.
Do not discontinue abruptly; follow dosing instructions carefully.

Special Considerations

Black Box Warnings:

Potential for severe hypotension leading to syncope.
Risk of hemolytic anemia with long-term therapy.

Genetic Factors: None specified.

Lab Test Interference: None known.

Overdose Management

Signs/Symptoms: Severe hypotension, dizziness, weakness, syncope.

Treatment: Supportive care; vasopressors may be used; also, gastric lavage and activated charcoal if ingestion was recent.

Storage and Handling

Storage: Store at room temperature, away from moisture and light.

Stability: Stable under recommended storage conditions.