Classifications: nonnitrate vasodilator; antihypertensive;
Therapeutic: antihypertensive

Pregnancy Category: C


10 mg, 25 mg, 50 mg, 100 mg tablets; 20 mg/mL vial


Reduces BP mainly by direct effect on vascular smooth muscles of arterial-resistance vessels, resulting in vasodilation. Has little effect on venous-capacitance vessels. Hypotensive effect may be limited by sympathetic reflexes that increase heart rate, stroke volume, and cardiac output.

Therapeutic Effect

Reduces BP with diastolic response often being greater than systolic response. Vasodilation reduces peripheral resistance and substantially improves cardiac output, and renal and cerebral blood flow.


Most commonly in stepped-care approach to treat moderate to severe hypertension. Also in early malignant hypertension and resistant hypertension that persists after sympathectomy.

Unlabeled Uses

Conjunctively with cardiac glycosides and other vasodilators in short-term treatment of acute CHF; unexplained pulmonary hypertension; eclampsia.


Coronary artery disease, mitral valvular rheumatic heart disease, MI, tachycardia, SLE; pregnancy (category C).

Cautious Use

Cerebrovascular accident, advanced renal impairment, coronary heart disease, renal disease; renal failure; use with MAO INHIBITORS.

Route & Dosage

Adult: PO 10–50 mg q.i.d. IM 10–50 mg q4–6h IV 10–20 mg q4–6h, may increase to 40 mg
Geriatric: PO Start with 10 mg 2–3 times/d
Child: PO 3–7.5 mg/kg/d in 4 divided doses IV/IM 0.1–0.2 mg/kg in divided doses (max 20 mg)

Renal Impairment
Clcr10–50 mL/min: dose q8h


  • Give with food; bioavailability is increased by taking it with food.
  • Discontinue gradually to avoid sudden rise in BP and acute heart failure.
  • Inform patients of the dangers of abrupt withdrawal.
  • Give deep into a large muscle.

PREPARE: Direct: Give undiluted. Use immediately after being drawn into syringe. Do not add to IV solutions.  

ADMINISTER: Direct: Give each 10 mg or fraction thereof over 1 min.  

INCOMPATIBILITIES Solution/additive: Aminophylline, ampicillin, chlorothiazide, edetate calcium disodium, ethacrynate, hydrocortisone, mephentermine, methohexital, nitroglycerin, phenobarbital, verapamil, D5W. Y-site: Aminophylline, ampicillin, diazoxide, furosemide.

  • Store at 15°–30° C (59°–86° F) in tight, light-resistant containers unless otherwise directed. Avoid freezing.

Adverse Effects (≥1%)

Body as a Whole: Hypersensitivity (rash, urticaria, pruritus, fever, chills, arthralgia, eosinophilia, cholangitis, hepatitis, obstructive jaundice). CNS: Headache, dizziness, tremors. CV: Palpitation, angina, tachycardia, flushing, paradoxical pressor response. Overdose: arrhythmia, shock. Special Senses: Lacrimation, conjunctivitis. GI: Anorexia, nausea, vomiting, diarrhea, constipation, abdominal pain, paralytic ileus. Urogenital: Difficulty in urination, glomerulonephritis. Hematologic: Decreased hematocrit and hemoglobin, anemia, agranulocytosis (rare). Other: Nasal congestion, muscle cramps, SLE-like syndrome, fixed drug eruption, edema.

Diagnostic Test Interference

Positive direct Coombs' tests in patients with hydralazine-induced SLE. Hydralazine interferes with urinary 17-OHCS determinations (modified Glenn-Nelson technique).


Drug: beta blockers and other antihypertensive agents compound hypotensive effects.


Absorption: Readily absorbed from GI tract. Onset: 20–30 min. Peak: 2 h. Duration: 2–6 h. Distribution: Crosses placenta; distributed into breast milk. Metabolism: In liver. Elimination: 90% in urine; 10% in feces. Half-Life: 2–8 h.

Nursing Implications

Assessment & Drug Effects

  • Lab tests: Determine antinuclear antibody titer before initiation of therapy and periodically during prolonged therapy.
  • Make baseline and periodic determinations of BUN, creatinine clearance, uric acid, serum potassium, blood glucose, and ECG.
  • Monitor for S&S of SLE, especially with prolonged therapy.
  • Monitor BP and HR closely. Check every 5 min until it is stabilized at desired level, then every 15 min thereafter throughout hypertensive crisis.
  • Monitor I&O when drug is given parenterally and in those with renal dysfunction.

Patient & Family Education

  • Monitor weight, check for edema, and report weight gain to physician.
  • Note: Some patients experience headache and palpitations within 2–4 h after first PO dose; symptoms usually subside spontaneously.
  • Make position changes slowly and avoid standing still, hot baths/showers, strenuous exercise, and excessive alcohol intake.
  • Do not drive or engage in other potentially hazardous activities until response to drug is known.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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