Guanethidine: Indication, Dosage, Side Effect, Precaution

This information is not country-specific. Please refer to the local prescribing information.

Generic Medicine Info

Indications and Dosage

Intramuscular
Hypertensive crisis

Adult: As monosulfate: 10-20 mg as a single dose.

Ophthalmic
Open-angle glaucoma

Adult: As monosulfate: 5% eye drops without adrenaline or, 1% or 3% with adrenaline 0.2% or 0.5%, respectively.

Ophthalmic
Lid retraction accompanying hyperthyroidism

Adult: As monosulfate: 5% eye drops.

Oral
Hypertension

Adult: As monosulfate: 10 mg daily, increased by increments of 10 mg every 5-7 days according to response. Maintenance: 25-50 mg once daily .
Child: As monosulfate: 200 mcg/kg daily with increments of 200 mcg/kg every 7-10 days, according to response.

Contraindications

Pheochromocytoma; heart failure not caused by hypertension.

Special Precautions

Renal impairment, cerebrovascular disorders, ischaemic heart disease, history of peptic ulcer or asthma. Hypotensive effect may be increased by exercise and heat. Increased risk of CV collapse or cardiac arrest in patients undergoing surgery. Eye drops: Examine regularly for signs of conjunctival damage.

Adverse Reactions

Severe postural and exertional hypotension, diarrhoea, dizziness, syncope, muscle weakness, lassitude, angina, renal insufficiency, transient cerebral ischaemia, bradycardia, failure of ejaculation, fatigue, headache, salt and water retention, oedema, breathlessness, overt heart failure, nausea, vomiting, dry mouth, nasal congestion, parotid tenderness, blurring of vision, depression, myalgia, muscle tremor, paresthesias, hair loss, dermatitis, disturbed micturition, priapism, aggravation or precipitation of asthma, exacerbation of peptic ulcer, haematological effects. Eye drops: Conjunctival hyperaemia, miosis, burning sensations, ptosis, superficial punctate keratitis.

Drug Interactions

Adrenaline, amphetamine, other sympathomimetics, tricyclic antidepressants, MAOIs, phenothiazine derivatives and related antipsychotics, oral contraceptives, digoxin or other digitalis derivatives, thiazide diuretics, other antihypertensives, levodopa, alcohol.

Action

Description: Guanethidine acts by selectively inhibiting transmission in postganglionic adrenergic nerves. It acts mainly by preventing the release of noradrenaline at nerve endings. It does not prevent catecholamine secretion by the adrenal medulla. When applied topically to the eye, guanethidine reduces the production of aqueous humor.
Pharmacokinetics:
Absorption: Absorption from GI tract is variable and incomplete absorbed; <50% of the dose reaches the systemic circulation.
Metabolism: Partially metabolised in the liver.
Excretion: Urine as metabolites and unchanged guanethidine. Terminal half-life: About 5 days.

Storage

Store <30°C.

MIMS Class

Antiglaucoma Preparations / Other Antihypertensives

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