- Drugs List
- Therapeutic Indications
- Precautions and Warnings
- Pregnancy and Lactation
- Side Effects
Injection formulation of guanethidine.
Hypertension - crisis
The recommended dose is one injection of 10 to 20 mg. This will generally cause a fall in blood pressure within 30 minutes which reaches a maximum in 1 to 2 hours and is maintained for 4 to 6 hours. If a further dose of 10 to 20 mg is deemed necessary, then 3 hours should be allowed to elapse between doses.
(See Dosage; Adult)
Concurrent coronary or cerebral insufficiency should be taken into account.
Patients with Renal Impairment
The Renal Drug Handbook suggests the following doses:
Glomerular Filtration Rate (GFR)
GFR 20 to 50 ml/minute: Give every 24 hours.
GFR 10 to 20 ml/minute: Give every 24 hours.
GFR less than 10 ml/minute: Give every 24 to 36 hours; use with caution.
For intramuscular injection.
Children under 18 years
Within 2 weeks of discontinuing MAOIs
Cardiac failure unless due to hypertensive crisis
First trimester of pregnancy
Renal impairment - creatinine clearance below 40ml/minute
Precautions and Warnings
History of peptic ulcer
Renal impairment - creatinine clearance 40-65ml/minute
Second trimester of pregnancy
Third trimester of pregnancy
Adjustment of hypoglycaemic therapy may be necessary in diabetes mellitus
Advise ability to drive/operate machinery may be affected by side effects
Heat or physical exertion may increase antihypertensive effect
May cause cardiac failure in prolonged use
Patients with fluid retention should be treated with diuretics
Discontinue prior to surgery
Decrease the dose if patient develops a fever
Guanethidine should be used with caution in patients with Parkinson's disease with associated autonomic neuropathy because of potential risk of worsening of orthostatic hypotension.
Pregnancy and Lactation
Use guanethidine with caution during pregnancy.
Avoid use during the first trimester and the last two weeks prior to the birth or during labour as it may induce paralytic ileus in the infant.
Briggs (2011) concludes that use of this potent antihypertensive have been supplanted by the use of safer, more effective agents for pregnant women and that guanethidine should be considered as a drug of last choice during pregnancy.
The use of all medication in pregnancy should be avoided whenever possible; particularly in the first trimester. Non-drug treatments should also be considered. When essential, a medication with the best safety record over time should be chosen, employing the lowest effective dose for the shortest possible time. Polypharmacy should be avoided. Teratogens taken in the pre-embryonic period, often quoted as lasting until 14 to 17 days post-conception, are believed to have an all-or-nothing effect. Where drugs have a short half-life, and when the date of conception is certain, this may allow women to be reassured where drug exposure has occurred within this time frame. Further advice may be available from the UK National Teratology Information Service (NTIS) and through ToxBase, available via password on the internet ( www.toxbase.org ) or if this is unavailable at the backup site ( www.toxbasebackup.org ).
Use guanethidine with caution during breastfeeding.
Although guanethidine passes into breast milk the quantities are so small that there are no expected undesirable effects on the infant.
Neonates, infants born prematurely, those with low birth weight, those with an unstable gastrointestinal function or who have serious illnesses may require special consideration. For any infant, if a drug is prescribed to the nursing mother, it should be at the lowest practical dose and for the shortest time. When drug administration is unavoidable and breastfeeding is to continue, minimisation of exposure of the infant to the drug may sometimes be achieved by timing the maternal doses to just after a feeding episode. Infants exposed to drugs via breast milk should be monitored for unusual signs or symptoms. Interactions between the drug received by the infant from the mother's milk and medication prescribed for the infant should also be considered, for example, when the drug given to the infant may prevent metabolism of the drug received via breast milk.
Specialist advice is available from the UK Drugs in Lactation Advisory Service at https://www.midlandsmedicines.nhs.uk/content.asp?section=6&subsection=17&pageIdx=1
Exacerbation of intermittent claudication
Failure of ejaculation
Increase in blood urea nitrogen
Parotid gland swelling
It is strongly recommended that the UK National Poisons Information Service be consulted on cases of suspected or actual overdose where there is doubt over the degree of risk or about appropriate management.
The following number will direct the caller to the relevant local centre (0844) 892 0111
Information may be obtained if you have access to ToxBase the primary clinical toxicology database of the National Poisons Information Service. This is available via password on the internet ( www.toxbase.org ) or if this is unavailable at the backup site ( www.toxbasebackup.org ).
Last Full Review Date: November 2013
Drugs in Pregnancy and Lactation: A Reference Guide to Fetal and Neonatal Risk, 9th edition (2011) ed. Briggs, G., Freeman, R. and Yaffe, S. Lippincott Williams & Wilkins, Philadelphia.
Joint Formulary Committee. British National Formulary. 66th ed. London: BMJ Group and Pharmaceutical Press; 2013. Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press
Martindale: The Complete Drug Reference, 37th edition (2011) ed. Sweetman, S. Pharmaceutical Press, London.
Summary of Product Characteristics: Ismelin/Guanethidine monosulfate ampoules 10mg/ml. Amdipharm Mercury Company Ltd. Revised September 2013.
The Renal Drug Handbook. 3rd edition. (2009) ed. Ashley, C and Currie, Radcliffe Publishing Ltd, Abingdon.
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