Generic Medicine Info
Indications and Dosage
Hypertensive crisis
Adult: 10-20 mg as a single dose, a further dose of 10-20 mg may be given after 3 hours, if necessary.
Renal Impairment
CrCl (mL/min) Dosage
10-40 Contraindicated.
41-65 Dose reduction or longer intervals between doses may be required.
Phaeochromocytoma, heart failure unrelated to hypertension. Concomitant use or within 2 weeks of MAOIs. Severe renal impairment (CrCl 10-40 mL/min).
Special Precautions
Patient with coronary or cerebral artery disease, asthma, history of gastrointestinal ulceration, Parkinson’s disease with associated autonomic neuropathy. Moderate renal impairment (CrCl 41-65 mL/min). Pregnancy (not recommended during the 1st trimester or within 2 weeks before labour) and lactation. Withdraw treatment few days prior to surgery.
Adverse Reactions
Significant: CNS effect (e.g. dizziness, blurred vision, drowsiness), latent heart failure (prolonged use), fever.
Cardiac disorders: Bradycardia, sick-sinus syndrome.
Gastrointestinal disorders: Nausea, diarrhoea, vomiting, dry mouth, gaseous distension.
General disorders and administration site conditions: Lethargy, oedema, tiredness.
Investigations: Increased BUN levels (in patients with latent or manifest renal failure).
Nervous system disorders: Headache, paraesthesia.
Renal and urinary disorders: Uraemia (in patients with latent or manifest renal failure).
Reproductive system and breast disorders: Ejaculation disturbances, erectile dysfunction (including priapism).
Respiratory, thoracic and mediastinal disorders: Rarely, asthma.
Vascular disorders: Postural hypotension, exacerbation of intermittent claudication.
Patient Counseling Information
This drug may cause dizziness, drowsiness, or blurred vision, if affected, do not drive or operate machinery.
Monitoring Parameters
Monitor blood pressure and renal function.
Symptoms: Postural hypotension causing syncope, sinus bradycardia, tiredness, dizziness, tachycardia, blurred vision, muscle weakness, nausea, vomiting, severe diarrhoea, and oliguria. Management: Symptomatic treatment. In case of postural hypotension, keep the patient in a recumbent position or institute fluid and electrolyte replacement; if necessary, may administer pressor agents. Administer atropine for sinus bradycardia. Treat diarrhoea with an anticholinergic agent.
Drug Interactions
May lead to sinus bradycardia when given concurrently with antiarrhythmic agents and digitalis. Antihypertensive effect may be increased by reserpine, methyldopa, vasodilators (e.g. minoxidil), calcium channel blockers, β-blockers, ACE inhibitors. Antihypertensive effect may be decreased by TCAs, phenothiazine derivatives, chlorpromazine, oral contraceptives. May increase hypersensitivity to adrenaline, amphetamines, or other sympathomimetic agents.
Potentially Fatal: May lead to release of large quantities of catecholamines causing hypertensive crisis when given to patient previously treated with MAOIs.
Food Interaction
Alcohol may enhance the antihypertensive effect of guanethidine.
Mechanism of Action: Guanethidine is a peripheral sympathetic blocking agent. It lowers blood pressure by depleting and inhibiting reformation of noradrenaline in postganglionic nerve endings, but it does not prevent the secretion of catecholamines by the adrenal medulla.
Onset: Fall in blood pressure: Within 30 minutes.
Distribution: Enters breast milk (small amounts).
Metabolism: Partially metabolised in the liver.
Excretion: Via urine as metabolites and unchanged drug. Terminal half-life: Approx 5 days.
Chemical Structure

Chemical Structure Image

Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 3518, Guanethidine. Accessed Mar. 25, 2021.

MIMS Class
Other Antihypertensives
ATC Classification
C02CC02 - guanethidine ; Belongs to the class of guanidine derivatives, peripherally-acting antiadrenergic agents. Used in the treatment of hypertension.
Anon. Guanethidine. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. Accessed 09/03/2021.

Buckingham R (ed). Guanethidine Monosulfate. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. Accessed 09/03/2021.

Ismelin 10 mg/mL Ampoules (Amdipharm UK Limited). MHRA. Accessed 09/03/2021.

Disclaimer: This information is independently developed by MIMS based on Guanethidine from various references and is provided for your reference only. Therapeutic uses, prescribing information and product availability may vary between countries. Please refer to MIMS Product Monographs for specific and locally approved prescribing information. Although great effort has been made to ensure content accuracy, MIMS shall not be held responsible or liable for any claims or damages arising from the use or misuse of the information contained herein, its contents or omissions, or otherwise. Copyright © 2024 MIMS. All rights reserved. Powered by
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