Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.
Quick facts
- How it is given
- intramuscular, intravenous
- Type
- human prescription drug
- RxNorm ID
- 966571
We do not publish dosing. How much of this medicine to take, how often, and for how long depends on your age, weight, kidney and liver function, other conditions and other medicines. That is a decision for the person who prescribes or dispenses it. Follow the directions on your own pack and ask your pharmacist if anything is unclear.
What it is used to treat
INDICATIONS AND USAGE Severe essential hypertension when the drug cannot be given orally or when there is an urgent need to lower blood pressure.
About this medicine
DESCRIPTION HydrALAZINE Hydrochloride Injection, USP is an antihypertensive available in a 1 mL vial for intravenous and intramuscular administration. Each milliliter of the sterile, nonpyrogenic colorless solution contains Hydralazine Hydrochloride, 20 mg, Methylparaben, 0.65 mg, Propylparaben, 0.35 mg, Propylene Glycol, 103.6 mg, and Water for Injection q.s. The pH of the solution is 3.4 to 4.4. pH may be adjusted with Hydrochloric Acid and/or Sodium Hydroxide. Hydralazine Hydrochloride is 1-Hydrazinophthalazine monohydrochloride, and its structural formula is: Molecular Formula C 8 H 8 N 4 HCl Hydralazine Hydrochloride USP is a white to off-white, odorless crystalline powder. It is soluble in water, slightly soluble in alcohol, and very slightly soluble in ether. It melts at about 275°C, with decomposition, and has a molecular weight of 196.64. Adobe Systems
Who should not take it
CONTRAINDICATIONS Hypersensitivity to hydralazine; coronary artery disease; mitral valvular rheumatic heart disease.
Warnings
WARNINGS In a few patients hydralazine may produce a clinical picture simulating systemic lupus erythematosus including glomerulonephritis. In such patients hydralazine should be discontinued unless the benefit-to-risk determination requires continued antihypertensive therapy with this drug. Symptoms and signs usually regress when the drug is discontinued but residua have been detected many years later. Long-term treatment with steroids may be necessary. (See PRECAUTIONS, Laboratory Tests . )
Reported side effects
ADVERSE REACTIONS Adverse reactions with hydralazine hydrochloride are usually reversible when dosage is reduced. However, in some cases it may be necessary to discontinue the drug. The following adverse reactions have been observed, but there has not been enough systematic collection of data to support an estimate of their frequency. Common: Headache, anorexia, nausea, vomiting, diarrhea, palpitations, tachycardia, angina pectoris. Less Frequent: Digestive: constipation, paralytic ileus. Cardiovascular: hypotension, paradoxical pressor response, edema. Respiratory: dyspnea. Neurologic: peripheral neuritis, evidenced by paresthesia, numbness, and tingling; dizziness; tremors; muscle cramps; psychotic reactions characterized by depression, disorientation, or anxiety. Genitourinary: difficulty in urination. Hematologic: blood dyscrasias, consisting of reduction in hemoglobin and red cell count, leukopenia, agranulocytosis, purpura; lymphadenopathy; splenomegaly. Hypersensitive Reactions: rash, urticaria, pruritus, fever, chills, arthralgia, eosinophilia, and, rarely, hepatitis. Other: nasal congestion, flushing, lacrimation, conjunctivitis.
Interactions with other medicines
Drug Interactions MAO inhibitors should be used with caution in patients receiving hydralazine. When other potent parenteral antihypertensive drugs, such as diazoxide, are used in combination with hydralazine, patients should be continuously observed for several hours for any excessive fall in blood pressure. Profound hypotensive episodes may occur when diazoxide injection and hydralazine injection are used concomitantly.
If too much is taken
OVERDOSAGE Acute Toxicity: No deaths due to acute poisoning have been reported. Highest known dose survived: adults, 10 g orally. Oral LD 50 in rats: 173 and 187 mg/kg. Signs and Symptoms: Signs and symptoms of overdosage include hypotension, tachycardia, headache, and generalized skin flushing. Complications can include myocardial ischemia and subsequent myocardial infarction, cardiac arrhythmia, and profound shock. Treatment: There is no specific antidote. Support of the cardiovascular system is of primary importance. Shock should be treated with plasma expanders. If possible, vasopressors should not be given, but if a vasopressor is required, care should be taken not to precipitate or aggravate cardiac arrhythmia. Tachycardia responds to beta blockers. Digitalization may be necessary, and renal function should be monitored and supported as required. No experience has been reported with extracorporeal or peritoneal dialysis.
Before you take anything new
Tell your pharmacist or doctor about every medicine you take — including ones bought without a prescription, herbal products and supplements. Interactions are one of the most common avoidable causes of harm from medicines, and a pharmacist can check your full list in a couple of minutes.
This page is built from the openFDA record of the U.S. Food and Drug Administration's approved labelling for this product, effective 6 May 2019. Label text has been shortened and reformatted for readability; safety wording has not been altered in meaning. FDA labelling describes products approved in the United States — brand names, strengths, formulations and approved uses may differ in your country. Always read the leaflet that comes with your own pack. PocketsInfo is not affiliated with, and is not endorsed by, the FDA. Retrieved 2026-07-30.