nitroprusside sodium (Rx)

Frequency Not Defined

Common

• Bradyarrhythmia, hypotension, palpitations, tachyarrhythmia
• Apprehension, restlessness, confusion, dizziness, headache, somnolence
• Rash, sweating
• Thyroid suppression
• Injection site irritation
• Muscle twitch
• Oliguria, renal azotemia

Serious

• Cardiac dysrhythmia, hemorrhage, decreased platelet aggregation, excessive hypotensive response
• Raised intracranial pressure
• Metabolic acidosis
• Bowel obstruction
• Methemoglobinemia
• Cyanide poisoning
• Thiocyanate toxicity

Contraindications

Hypersensitivity

Compensatory HTN (eg, arteriovenous shunt or aortic coarctation); (for controlled hypotension): inadequate cerebral circulation

Certain rare conditions, eg, congenital optic atrophy, tobacco amblyopia

Treatment of acute CHF associated with reduced peripheral vascular resistance such as high-output heart failure that may be seen in endotoxic sepsis

To produce hypotension during surgery in patients with known inadequate cerebral circulation, or in moribund patients (A.S.A. Class 5E) coming to emergency surgery

Cautions

Small transient excesses in the infusion rate of sodium nitroprusside can result in excessive hypotension, sometimes to levels so low as to compromise the perfusion of vital organs; nitroprusside-induced hypotension will be self-limited within 1-10 minutes after discontinuation of therapy; during these few minutes, it may be helpful to put the patient into a head-down (Trendelenburg) position to maximize venous return; if hypotension persists more than a few minutes after discontinuation of infusion therapy is not the cause, and the true cause must be sought

Therapy can cause increases in intracranial pressure; in patients whose intracranial pressure is already elevated, sodium nitroprusside should be used only with extreme caution

Use caution when administering nitroprusside to patients with hepatic insufficiency

When sodium nitroprusside (or any other vasodilator) is used for controlled hypotension during anesthesia, the patient’s capacity to compensate for anemia and hypovolemia may be diminished; if possible, pre-existing anemia and hypovolemia should be corrected prior to administration of therapy

Hypotensive anesthetic techniques may cause abnormalities of pulmonary ventilation/perfusion ratio; patients intolerant of these abnormalities may require a higher fraction of inspired oxygen

Head trauma, increases ICP, hyponatremia, hypothyroidism, severe hepatic or renal impairment, elderly

Cyanide toxicity

• Infusions at rates above 2 mcg/kg/min generate cyanide ion (CN¯) faster than the body can normally dispose of it
• Methemoglobin normally present in the body can buffer a certain amount of CN¯, but the capacity is exhausted by the CN¯ produced from about 500 mcg/kg of sodium nitroprusside; this amount of sodium nitroprusside is administered in less than an hour when the drug is administered at 10 mcg/kg/min (the maximum recommended rate); thereafter, the toxic effects of CN¯ may be rapid, serious, and even lethal
• Cyanide toxicity may manifest itself as venous hyperoxemia with bright red venous blood, as cells become unable to extract oxygen delivered to them; metabolic (lactic) acidosis; air hunger; confusion; and death
• Cyanide toxicity due to causes other than nitroprusside has been associated with angina pectoris and myocardial infarction; ataxia, seizures, and stroke; and other diffuse ischemic damage
• Hypertensive patients, and patients concomitantly receiving other antihypertensive medications, may be more sensitive to the effects of sodium nitroprusside than normal subjects
• Check thiocyanate levels, monitor pulse oximeter
• Thiocyanate clearance may decrease with renal failure

Drug interaction overview

• The hypotensive effect of sodium nitroprusside is augmented by that of most other hypotensive drugs, including ganglionic blocking agents, negative inotropic agents, and inhaled anesthetics

Pregnancy Category: C

Lactation: not known if distributed into milk

Pregnancy Categories

A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

NA: Information not available.

Mechanism of Action

Relaxes vascular smooth muscle to reduce afterload and preload by producing NO

Dilates coronary arteries

Pharmacokinetics

Half-Life: Parent drug: 2 min, metabolite (thiocyanate): 3 days, longer in patients with impaired renal function or hyponatremia

Onset of action: <2 min

Duration: 1-10 min

Metabolism: in blood (100%); ferrous ion in nitroprusside molecule reacts rapidly with sulfhydryl compounds in RBCs which results in cyanide release, which is then metabolized in liver and kidney by rhodanese to thiocyanate

Metabolites: Thiocyanate (inactive)

Excretion: Mainly in urine, excreted entirely as metabolites, principally thiocyanate

Dialyzable: Yes (HD)

IV Incompatibilities

Additive: atracurium

Y-site: amiodarone(?), cisatracurium (at 2+ mg/mL cisatra, may be compatible at 0.1 mg/mL cisatra), haloperidol (at 5 mg/mL halo, may be compatible at 0.5 mg/mL halo), levofloxacin, propafenone(?)

IV Compatibilities

Solution: D5W, LR, NS (when not exposed to bright light)

Additive: cimetidine, enalaprilat, ranitidine, verapamil

Syringe: caffeine, heparin

Y-site: alprostadil, atracurium, bivalirudin, CaCl2, dexmedetomidine, diltiazem, dobutamine, dopamine, enalaprilat, esmolol, famotidine, furosemide, heparin, hetastarch, inamrinone, insulin, isoproterenol, labetalol, lidocaine, MgSO4, midazolam, morphine sulfate, nicardipine, nitroglycerin, pancuronium, KCl, potassium phosphates, procainamide, propofol, tacrolimus, theophylline, vecuronium

IV Preparation

Reconstitute 50 mg vial in 2-3 mL D5W or SWI (NOT BWI, increases decomposition rate)

Dilute reconstituted solution (or 25 mg/mL vial, contains 2 mL) with 250-1000 mL D5W (final conc 50-200 mcg/mL)

Wrap container in aluminum foil

Solution should be reddish-brown; discard if blue

Do not freeze

Use within 24 hr

Protect from light, do not use if discolored

IV Administration

Infusion pump required

Undiluted vial not for direct injection