Classifications: nonnitrate vasodilator;
Therapeutic: nonnitrate vasodilator

Prototype: Hydralazine
Pregnancy Category: C


150 mg sustained release capsule; 30 mg/mL injection


Exerts nonspecific direct spasmolytic effect on smooth muscles unrelated to innervation. Action is especially pronounced on coronary, cerebral, pulmonary, and peripheral arteries when spasm is present. Acts directly on myocardium, depresses conduction and irritability, and prolongs refractory period.

Therapeutic Effect

Relaxes the smooth muscle of the heart as well as produces relaxation of the vascular smooth muscles.


Primarily for relief of cerebral and peripheral ischemia associated with arterial spasm and MI complicated by arrhythmias. Also visceral spasm as in ureteral, biliary, and GI colic.

Unlabeled Uses

Impotence, cardiac bypass surgery.


Parenteral use in complete AV block; pregnancy (category C); lactation.

Cautious Use

Glaucoma; myocardial depression; glaucoma; QT prolongation, angina pectoris; recent stroke.

Route & Dosage

Cerebral and Peripheral Ischemia
Adult: PO 150–300 mg q8–12h IM/IV 30–120 mg q3h as needed
Child: IM/IV 6 mg/kg/d divided into 4 doses


  • Give with or following meals; give milk or prescribed antacid to reduce possibility of nausea.
  • Ensure that sustained release form is not chewed or crushed. Must be swallowed whole.
  • Aspirate carefully before injecting IM to avoid inadvertent entry into blood vessel, and administer slowly.
  • IV administration to children: Verify correct IV concentration and rate of infusion with physician.

PREPARE: Direct: Give undiluted or diluted in an equal volume of sterile water for injection.  

ADMINISTER: Direct: Give slowly over 1–2 min. AVOID rapid injection.  

INCOMPATIBILITIES Solution/additive: Aminophylline, heparin.

Adverse Effects (≥1%)

Body as a Whole: General discomfort, facial flushing, sweating, weakness, coma. CNS: Dizziness, drowsiness, headache, sedation. CV: Slight rise in BP, paroxysmal tachycardia, transient ventricular ectopic rhythms, AV block, arrhythmias. GI: Nausea, anorexia, constipation, diarrhea, abdominal distress, dry mouth and throat, hepatotoxicity (jaundice, eosinophilia, abnormal liver function tests); with rapid IV administration. Respiratory: Increased depth of respiration, respiratory depression, fatal apnea. Skin: Pruritus, skin rash. Special Senses: Diplopia, nystagmus. Urogenital: Priapism.


Drug: May decrease levodopa effectiveness; morphine may antagonize smooth muscle relaxation effect of papaverine.


Absorption: Readily from GI tract. Peak: 1–2 h. Duration: 12 h sustained release. Metabolism: In liver. Elimination: In urine chiefly as metabolites. Half-Life: 90 min.

Nursing Implications

Assessment & Drug Effects

  • Monitor pulse, respiration, and BP in patients receiving drug parenterally. If significant changes are noted, withhold medication and report promptly to physician.
  • Lab tests: Perform liver function and blood tests periodically. Hepatotoxicity (thought to be a hypersensitivity reaction) is reversible with prompt drug withdrawal.

Patient & Family Education

  • Notify physician if any adverse effect persists or if GI symptoms, jaundice, or skin rash appear. Liver function tests may be indicated.
  • Do not drive or engage in potentially hazardous activities until response to drug is known. Alcohol may increase drowsiness and dizziness.

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

© 2006-2022 Last Updated On: 11/25/2022 (0)
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