This site is intended for UK healthcare professionals
Medscape UK Univadis Logo
Medscape UK Univadis Logo

Hydralazine parenteral


Injection/infusions of hydralazine.

Drugs List

  • hydralazine 20mg powder for solution for injection
  • Therapeutic Indications


    Hypertension - crisis
    Hypertension - in pregnancy

    Unlicensed Uses




    By slow intravenous injection
    Initially 5mg to 10mg.
    If required, repeat injection after 20 to 30 minutes.
    Continuous monitoring of blood pressure and heart rate is required; a suitable response is defined as a fall in diastolic blood pressure to 90/100mmHg.

    By continuous intravenous infusion
    Initially a flow rate of 200micrograms/minute to 300micrograms/minute.
    Maintenance flow rates should be determined individually and are usually within the range of 50micrograms/minute to 150micrograms/minute.


    Hypertension (unlicensed)
    By slow intravenous injection
    Children aged 12 to 18 years: 5mg to 10mg, repeated every 4 to 6 hours as necessary.
    Children aged 1 month to 12 years: 100micrograms/kg to 500micrograms/kg repeated every 4 to 6 hours as necessary. Maximum dose is 3mg/kg or 60mg daily.

    By continuous intravenous infusion (preferred route in cardiac patients)
    Children aged 12 to 18 years: 3mg/hour to 9mg/hour. Maximum dose is 3mg/kg daily.
    Children aged 1 month to 12 years: 12.5 to 50micrograms/kg/hour. Maximum dose is 3mg/kg daily.


    Hypertension (unlicensed)
    By slow intravenous injection
    100micrograms/kg to 500micrograms/kg repeated every 4 to 6 hours as necessary. Maximum dose is 3mg/kg daily.

    By continuous intravenous infusion (preferred route in cardiac patients)
    12.5 to 50micrograms/kg/hour. Maximum dose is 2mg/kg daily.

    Patients with Renal Impairment

    The dose of hydralazine should be reduced or the dosage interval prolonged in adult patients with renal impairment (creatinine clearance below 30ml/minute or serum creatinine concentrations greater than 2.5mg/100ml or 221 micromoles/l).

    The Renal Drug Handbook suggests the following doses based on Glomerular Filtration Rate (GFR):
    GFR less than or equal to 50ml/minute: Start at low dose and adjust in accordance with response.

    Patients with Hepatic Impairment

    The dose of hydralazine should be reduced or the dosage interval prolonged in patients with hepatic impairment.

    Additional Dosage Information

    Initial slow intravenous injection avoids precipitous decreases in arterial pressure with a critical reduction in cerebral or utero-placental perfusion.


    For slow intravenous injection or continuous intravenous infusion.


    Aortic stenosis
    Cardiac failure secondary to pulmonary disorder
    Congestive cardiac failure secondary to mechanical obstruction
    Constrictive pericarditis
    Dissecting aortic aneurysm
    First trimester of pregnancy
    High output cardiac failure
    Mitral stenosis
    Second trimester of pregnancy
    Severe tachycardia
    Systemic lupus erythematosus

    Precautions and Warnings

    Children under 18 years
    Cerebrovascular disorder
    Hepatic impairment
    Ischaemic heart disease
    Recent myocardial infarction (until stabilised)
    Renal impairment - creatinine clearance below 30 ml/minute
    Slow acetylator status
    Third trimester of pregnancy

    Reduce dose in patients with creatinine clearance below 30ml/min
    Reduce dose in patients with hepatic impairment
    Advise ability to drive/operate machinery may be affected by side effects
    Monitor blood pressure continuously
    Assess risk/benefit of treatment if symptoms of peripheral neuropathy occur
    Breastfeeding: Monitor infant for systemic effects of treating the mother
    Monitor ANF and urine every 6 months during long term therapy
    Avoid abrupt withdrawal
    Discontinue and investigate if symptoms of lupus-like syndrome develop
    Discontinue if blood dyscrasia develops
    Discontinue if fever occurs
    Discontinue treatment if rash occurs
    Maintain treatment at the lowest effective dose
    Hypotensive effects may be potentiated by alcohol

    In patients with coronary artery disease, hydralazine should only be given with concurrent beta-blockers or other suitable sympatholytic agents. Patients should be started on beta-blockers a few days before hydralazine therapy commences.

    Patients receiving hydralazine may experience a reduction in blood pressure when undergoing surgery. In these situations, epinephrine (adrenaline) should not be administered to correct the hypotension as this will enhance the cardiac-accelerating properties of hydralazine.

    Prolonged treatment (usually for more than 6 months) may provoke a systemic lupus erythematous (SLE) like syndrome, especially with doses in excess of 100mg daily. Primary symptoms are likely to be similar to rheumatoid arthritis (arthralgia, fever, anaemia, leucopenia, thrombocytopenia and rash) and are reversible after withdrawal of the drug. In its more severe form it resembles acute SLE (similar manifestations as the milder form plus pleurisy, pleural effusions and pericarditis), and in rare cases renal and ocular involvement have been reported. Early detection and a timely diagnosis with appropriate therapy (i.e. treatment discontinuation and possibly long term treatment with corticosteroids may be required to reverse these changes) are of the utmost importance in this life-threatening illness to prevent more severe complications, which may sometimes be fatal.

    Slow acetylators and women have an increased risk of developing a SLE-like syndrome and therefore the dosage should be kept below 100mg daily where possible and careful monitoring for signs and symptoms suggestive of the syndrome. If symptoms of SLE-like syndrome develop, hydralazine should be gradually withdrawn.

    The patient's acetylator status should be monitored before daily doses exceeding 100mg are recommended.

    Rapid acetylators often respond inadequately even to doses of 100mg daily and therefore the dose can be raised with only a slightly increased risk of SLE like syndrome.

    Microhaematuria and/or proteinuria, especially in conjunction with positive ANF titres may indicate the development of immune-complex glomerulonephritis associated with SLE-like syndrome. If these symptoms develop, hydralazine should be withdrawn immediately.

    If the discontinuation of hydralazine is necessary, the drug should be withdrawn gradually, except in serious situations such as SLE-like syndrome or blood dyscrasias. This gradual withdrawal reduces the risk of cardiac failure occurring or worsening.

    Pregnancy and Lactation


    Hydralazine is contraindicated in the first and second trimesters of pregnancy.

    Use hydralazine with caution in the third trimester of pregnancy

    The manufacturers state that use of hydralazine in pregnancy before the third trimester should be avoided, but the drug may be considered in later pregnancy if there are no safer alternatives or when the disease itself carries serious risks for the mother or child, e.g. pre-eclampsia and/or eclampsia.

    Hydralazine readily crosses the placenta. Serum concentrations in the foetus are equal to or greater than those in the mother (Briggs, 2011).

    Only use in later pregnancy if there is no alternative. Caution is advised although there have been few adverse effects in human pregnancy reported to date. Experience in the third trimester is extensive. However, neonatal thrombocytopenia and bleeding secondary to maternal ingestion of hydralazine has been reported infants of mothers who had consumed hydralazine daily throughout the third trimester. Other reports of symptomatic neonatal thrombocytopenia, leucopenia, petechial bleeding and haematomas have been reported after prenatal exposure (Schaefer, 2007). Therefore, chronic use should be reserved for refractory patients.

    There is a possibility that systemic vasodilation may be accompanied by decreased placental perfusion resulting in foetal/neonatal bradycardia (Schaefer, 2007).

    Hydralazine has been found to be teratogenic in mice, producing cleft palate and other bony malformations in doses ranging from 20mg/kg to 120mg/kg (20 to 30 times the maximum human daily dose. It was found not to be teratogenic in rats or rabbits.

    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 ( ) or if this is unavailable at the backup site ( ).


    Use hydralazine with caution in breastfeeding.

    Where hydralazine treatment is essential for breastfeeding mothers, they may receive therapy and the infant should be observed for possible adverse effects of hypotension, sedation and weakness.

    Hydralazine is excreted into breast milk and has been reported to achieve a milk: plasma ratio of 1.4. So far there are no reports that have shown adverse effects on the infant. Caution is advised and if used during breastfeeding, infants should be monitored. Schaefer (2007) concludes that hydralazine is among the antihypertensives of choice during breastfeeding.

    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

    Side Effects

    Abnormal liver function
    Acute renal failure
    Anginal pain
    Blood disorders
    Cardiac failure
    Fluid retention
    Gastro-intestinal disturbances
    Haemolytic anaemia
    Hypersensitivity reactions
    Hypertension (paradoxical)
    Increased lacrimation
    Joint swelling
    Lupus erythematosus-like syndrome
    Nasal congestion
    Ocular changes
    Orthostatic hypotension
    Paralytic ileus
    Peripheral neuritis
    Pleuritic pain
    Renal impairment
    Serum creatinine increased
    Thrombocytopenic purpura
    Urinary retention
    Weight loss


    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 ( ) or if this is unavailable at the backup site ( ).

    Further Information

    Last Full Review: January 2016

    Reference Sources

    Drugs During Pregnancy and Lactation: Treatment Options and Risk Assessment, 2nd edition (2007) ed. Schaefer, C., Peters, P. and Miller, R. Elsevier, London.

    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.

    Medications and Mothers' Milk, Sixteenth Edition (2014) Hale, T and Rowe, H, Hale Publishing, Plano, Texas.

    Summary of Product Characteristics: Hydralazine 20mg powder for concentration for solution for injection/infusion. Amdipharm Mercury Company Ltd. Revised December 2013.

    The Renal Drug Handbook. Fourth Edition (2014) ed. Ashley, C and Dunleavy, A, Radcliffe Publishing Ltd, London.

    NICE Evidence Services Available at: Last accessed: 25 August 2017

    US National Library of Medicine. Toxicology Data Network. Drugs and Lactation Database (LactMed).
    Available at:
    Hydralazine. Last revised: 10 March, 2015
    Last accessed: 27 January, 2016

    Access the full UK drug database with a FREE Medscape UK Account
    It takes just a few minutes, and you’ll get unlimited access to information on over 11,000 UK drugs.
    Register for Free

    Already a member? Log in

    Medscape UK | Univadis prescription drug monographs & interactions are based on FDB Multilex Content

    FDB Logo

    FDB Disclaimer : FDB Multilex is intended for the use of healthcare professionals and is provided on the basis that the healthcare professionals will retain FULL and SOLE responsibility for deciding what treatment to prescribe or dispense for any particular patient or circumstance.