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Hydralazine Hydrochloride


Pronunciation: high-DRAL-uh-zeen HIGH-droe-KLOR-ide
Class: Peripheral vasodilator

Trade Names

- Tablets 25 mg
- Tablets 50 mg
- Tablets 100 mg
- Injection 20 mg/mL

Apo-Hydralazine (Canada)


Directly relaxes vascular smooth muscle to cause peripheral vasodilation, decreasing arterial BP and peripheral vascular resistance.

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Hydralazine is rapidly absorbed. T max is 1 to 2 h and bioavailability is 30% to 50%.


Hydralazine is 87% protein bound.


Hydralazine is subject to polymorphic acetylation and undergoes extensive hepatic metabolism.


Hydralazine is excreted in urine mainly in the form of metabolites. The t ½ is 3 to 7 h.


Onset is 10 to 20 min (parenteral).


Duration is 6 to 12 h (oral) and 2 to 4 h (parenteral).

Special Populations

Slow acetylators

Slow acetylators generally have higher plasma levels of hydralazine and require lower doses to maintain control of BP.

Indications and Usage

Treatment of essential hypertension (oral form). Treatment of severe essential hypertension (parenteral form).

Unlabeled Uses

Reduction of overload in treatment of CHF, severe aortic insufficiency, and after valve replacement.


Coronary artery disease; mitral valvular rheumatic heart disease.

Dosage and Administration

Adjust individually.


PO Begin with 10 mg 4 times daily for 2 to 4 days; then 25 mg 4 times daily for 3 to 5 days; then 50 mg 4 times daily (max, 300 mg/day). IV/IM 20 to 40 mg repeated as needed.


PO 0.75 mg/kg/day in 4 divided doses initially; increase gradually over 3 to 4 wk to max 7.5 mg/kg/day or 200 mg/day. IV/IM 0.1 to 0.2 mg/kg/dose every 4 to 6 h as needed.

General Advice

  • Use parenteral form as soon as possible after drawing into syringe.
  • Parenteral solution discolors after contact with metal filter.
  • Administer tablets with food.


Store at room temperature.

Drug Interactions


May increase effect of hydralazine or effect of beta-blockers.


Effects of hydralazine may be decreased.

Laboratory Test Interactions

None well documented.

Adverse Reactions


Palpitations; tachycardia; angina pectoris; edema.


Headache; peripheral neuritis with paresthesias, numbness and tingling; dizziness; tremors; depression; disorientation; anxiety.


Lacrimation; conjunctivitis.


Anorexia; nausea; vomiting; diarrhea; constipation.


Blood dyscrasias; decreased hemoglobin; decreased RBC; leukopenia; agranulocytosis.


Hypersensitivity (eg, rash, urticaria, pruritus, fever, chills, arthralgia, eosinophilia); systemic lupus erythematosus.



Category C .


Excreted in breast milk.


Safety and efficacy have not been established by controlled clinical trials, but there is experience with its use.

Renal Function

Use drug with caution in patients with advanced renal damage.

Tartrazine Sensitivity

Some of these products contain tartrazine, which can cause allergic-type reactions in susceptible individuals, especially those who have aspirin hypersensitivity.

Lupus erythematosus

Drug may produce clinical picture similar to that with systemic lupus erythematosus (eg, arthralgia, dermatoses, fever, splenomegaly), including glomerulonephritis, when more than 50 mg/day is given for long periods. Symptoms usually reverse when drug is discontinued, but treatment may be required.



Hypotension, tachycardia, headache, flushing, MI, myocardial ischemia, cardiac arrhythmias, profound shock.

Patient Information

  • Instruct patient to take medication with meals to enhance absorption.
  • Caution patient to avoid abrupt discontinuation of drug to prevent sudden increase in BP.
  • Encourage patient to make lifestyle changes: weight reduction, sodium and alcohol restriction, discontinuance of smoking, regular exercise, behavior modification.
  • Advise patient to monitor BP and weight regularly.
  • Instruct patient to report sudden weight gain caused by fluid retention.
  • Advise patient to follow health care provider's orders for monitoring of CBC and other laboratory values.
  • Advise patient to avoid sudden changes in position or very hot baths to avoid orthostatic hypotension.
  • Caution patient not to take otc medications without consulting health care provider.
  • Instruct patient to report these symptoms to health care provider: prolonged tiredness, muscle or joint pain, chest pain, fever, numbness or tingling of hands or feet, rash.
  • Explain that drug may cause drowsiness and to use caution when driving or performing other tasks requiring mental alertness.

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