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Drug dosage identifier

Nitroprusside (Sodium Nitroprusside Dihydrate)

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Dose and administration

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  • 0.4-2.0 micrograms/kg/minute by continuous IV infusion.
  • Usual starting dose: 1 micrograms/kg/min; adjust rate as necessary to control BP.
  • Maximum dose: 10 micrograms/kg/min for 10 minutes.
  • Maximum infusion rate for prolonged therapy 2 micrograms/kg/min.
  • Sodium nitroprusside 5mg added to D5W to make 50ml = 100 micrograms/ml
  • 0.6ml/hr x weight (kg) = 1 microgram/kg/min 

Calculation Formula

Weight x 60 x   desired dose (micrograms/kg/min)  = rate in ml/hr
                                Strength of solution

Indications

Contraindications and precautions

  • Known hypersensitivity to sodium nitroprusside.
  • Coarctation of the aorta.
  • Arteriovenous fistula.
  • Compensatory hypertension.
  • Caution in preterm infants, especially extreme immaturity.
  • Caution in infants with hepatic or renal impairment.
  • Caution in infants with raised intracranial pressure.

Clinical pharmacology

Sodium nitroprusside is a potent, direct acting vasodilator. Affects arteriolar and venous smooth muscle equally. Has little effect on gastrointestinal or uterine smooth muscle, autonomic nervous system or central nervous system.

Rapid distribution to the target tissues (smooth muscle of the arteriolar and venous vessels). Rapid and complete metabolism within erythrocytes to cyanide and cyanomethaemoglobin. Metabolism of cyanide to thiocyanate by hepatic enzyme rhodanase. Repeated enterohepatic circulation. Very slow elimination of thiocyanate by the kidney (elimination half life 4-7 days).

Very rapid onset of action (1-2 minutes). Toxicity due to accumulation of cyanide and thiocyanate. Associated with marked vasodilation and hypotension.

Possible adverse effects

  • Hypotension
  • Cyanide toxicity
  • Metabolic acidosis
  • Restlessness, agitation, muscle twitching
  • Vomiting
  • Skin rash
  • Drug intolerance (metabolic acidosis, increased serum lactate and thiocyanate levels).
  • Methaemoglobinaemia.
  • Raised intracranial pressure.

Special considerations

  • The efficacy and safety of nitroprusside in neonates has not been established. Clinical experience is limited.
  • Titrate infusion rate against clinical response, especially blood pressure.
  • When discontinuing a nitroprusside infusion reduce the infusion rate steadily over a period of 10-30 minutes to avoid rebound hypertension.
  • Monitor haemoglobin (nitroprusside binds the haemoglobin), arterial blood gases for metabolic acidosis.
  • Serum thiocyanate levels should be measured. Toxic levels >2 mmol/L.
  • Management of thiocyanate or cyanide toxicity: stop nitroprusside infusion, infuse vitamin B12 0.1 mg/kg IV.

Management of Sodium Nitroprusside administration

Description

  • A reddish-brown powder for reconstitution 50 mg in amber coloured vials. Soluble in water.
  • Reconstituted solution has a faint brownish tinge.
  • Do NOT use if it is highly coloured.

Prescription

Charted on fluid chart giving:

  • rate in ml/hour
  • dose in micrograms/kg/minute

Also charted on drug chart under continuous infusions giving:

  • amount of drug to be added
  • base fluid, type and volume
  • micrograms/kg/ml

Administration

Continuous IV Infusion

  • Administered by a nurse with Neonatal IV Drug Certification.
  • Reconstitute with D5W to 10 mg/ml immediately prior to use.

      Nitroprusside 10 mg/ml
    Powder space: 0.0 ml
    D5W to be added: 5.0 ml
      50 mg in 5.0 ml
  • Dilute to make 100 mcg/ml in D5W by adding 5 mg sodium nitroprusside to make 50ml with D5W. Do NOT use any other diluent. Mix well. Filter prior to administration through a 5 micron filter.
  • Cover tubing and syringe in aluminium foil or other opaque material to protect from light.
  • Compatible ONLY with D5W. Do NOT mix with other drugs, IV solutions, blood or blood products. Use a separate line for sodium nitroprusside. Do NOT flush line.
  • Administer via a syringe pump.
  • Change solution and tubing every 24 hours.
  • Discard solution if any change in colour occurs.

Observation and documentation

  • Assess for signs of adverse effects.
  • Continuous cardiorespiratory monitoring.
  • Continuous blood pressure monitoring.
  • Monitor arterial blood gases for metabolic acidosis.
  • Monitor fluid balance.
  • Document vital signs hourly.
  • Monitor Hb. Nitroprusside binds to Hb.

Storage

  • At room temperature <30°C until reconstitution.
  • Protect from light, heat and moisture.
  • Reconstituted solutions should be protected from light by covering with tinfoil. Diluted solutions discard every 24 hours.

Selected References

  1. Roberts RJ. Drug therapy in infants: Pharmacologic principles and clinical experience. Philadelphia, WB Saunders, 1984; p 184-86.
  2. Greaney M, Saunders R (eds). NE Compendium: Detailed prescribing information. Auckland, Adis Press 1990; p129-31.
  3. Pawlak RP, Herfert LAT. Drug administration in the NICU. 2nd Ed 1991. Neonatal Network p190-191.

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Document Control

  • Date last published: 30 April 1997
  • Document type: Drug Dosage Guideline
  • Services responsible: ADHB Pharmacy, Neonatology
  • Editor: Sarah Bellhouse
  • Review frequency: 2 years