(and dosage form):
Contains sodium nitroprusside dihydrate 100 mg per vial.
A.7.1.3 Other hypotensives.
Sodium nitroprusside is a non-selective vasodilator. Regional distribution of blood flow is minimally affected by the agent. In general, renal blood flow and glomerular filtration are maintained and plasma renin activity increases. Sodium nitroprusside usually causes only a modest increase in heart rate and an overall reduction in myocardial oxygen demand.
For the reduction of blood pressure during anaesthesia in order to reduce bleeding in surgical procedures. For the treatment of hypertensive emergencies and the short-term reduction of cardiac preload and/or afterload where indicated.
Sensitivity to sodium nitroprusside.
SNP should not be used in the presence of compensatory hypertension (e.g. co-arctation of the aorta, arteriovenous shunt) and it is not indicated for chronic use. SNP should not be used in children until the safety, dosage and proper administration for paediatric usage has been established.
Safety in pregnancy and lactation has not been established.
Nitroprusside may worsen arterial hypoxaemia in patients with chronic obstructive pulmonary disease because it interferes with hypoxic pulmonary vasoconstriction and therefore promotes mismatching of ventilation and perfusion. Rebound hypertension may occur after abrupt cessation of short-term nitroprusside infusions; this may be caused by persistently elevated plasma renin concentrations.
It should be used with caution in patients with impaired renal or hepatic function or cerebrovascular insufficiency, or in patients with low plasma-cobalamin concentrations or Leber's optic atrophy.
DOSAGE AND DIRECTIONS FOR USE:
The solution should be prepared immediately before use. Protect from light during administration. Dissolve the contents of one vial (100 mg) of SNP in 5 mL of 0,9% saline, Ringers Lactate or 5% Dextrose in water and dilute to 1000 mL with the corresponding solutions. This provides a concentration of 100 mg/1000 mL or 100 ug/mL.
Depending on the indication and the level of hypotension required, the diluted solution should be infused at a rate of 0,3-3 ug/kg/min. The initial dose is 0,3 to 1 ug/kg/min increasing gradually under close supervision until the desired reduction in blood pressure is achieved. The average dose required to maintain blood pressure 30 to 40% below pre-treatment diastolic blood pressure is 3 ug/kg/min and the usual dose range is 0,5-6 ug/kg/min. The maximum recommended rate is about 8 ug/kg/min and infusions should be stopped after 10 minutes if there is no response.
For the induction of hypotension during anaesthesia, a maximum dose of 1,5 ug/kg/min is recommended.
Sodium nitroprusside must be administered as a continuous, controlled infusion and the patient must be closely observed.
Dilutions of SNP should not be kept for longer than 12 hours. The infusion should be discarded if it is highly coloured (blue, dark red or green). Solutions should be protected from light. Blood pressure must be monitored closely during administration.
SIDE-EFFECTS AND SPECIAL PRECAUTIONS:
Intravenous infusions of sodium nitroprusside may produce nausea and vomiting, apprehension, headache, dizziness, restlessness, perspiration, palpitations, retrosternal discomfort, abdominal pain, and muscle twitchings, but these effects may be reduced by slowing the rates of infusion.
Sodium nitroprusside is metabolised rapidly to cyanide and then thiocyanate. High plasma concentrations of thiocyanate may occur if treatment is continued for several days and may cause mental confusion, tinnitus, blurred vision, nausea, fatigue and ataxia.
If excessive amounts of SNP are given, cardiovascular collapse as well as toxic side effects (delirium, tinnitus and blurred vision) may occur as a result of excessive thiocyanate levels. With gross overdosages, cyanide intoxication is possible (dizziness, rapid breathing, headaches, sleepiness, tachycardia, cramps, unconsciousness).
SNP should be used with caution and initially in low doses in elderly patients as they may be more sensitive to the hypotensive response.
Care should be taken that extravasation does not occur.
Other hypotensive agents are known to augment the hypotensive effect of SNP and caution should be exercised when using the agents together. Thiocyanate inhibits both uptake and binding of iodine and SNP should therefore be used with caution in patients with hypothyroidism. Elimination of thiocyanate is dependent on adequate renal function and caution should be exercised in patients with renal insufficiency. Blood levels of thiocyanate should be determined daily when SNP is used for such patients, and values should not exceed 10 mg/100 mL.
KNOWN SYMPTOMS OF OVERDOSAGE AND PARTICULARS OF ITS TREATMENT:
The first sign of sodium nitroprusside overdosage is profound hypotension.
Metabolic acidosis may be an early indication of overdosage. This may be associated with or followed by headache, dyspnoea, vomiting, ataxia, dizziness and loss of consciousness. The administration of sodium nitroprusside should then be stopped immediately.
Overdosage may produce signs similar to those of cyanide poisoning with coma, absent reflexes, impalpable pulse, widely dilated pupils, pink colour, hypotension, distant heart sounds and very shallow breathing. Oxygen alone will not alleviate these symptoms and nitrites should be administered to induce methaemoglobin formation. The usual treatment for cyanide poisoning should be administered.
An orange-brown freeze-dried powder in a 5 mL amber glass vial.
Amber vials each containing 100 mg sodium nitroprusside dihydrate. Packed in outer containers containing 10 vials.
Store at 25°C. Protect from light. Keep out of reach of children.
The prepared solution should be protected against light and must be destroyed 12 hours after preparation.
NAME AND BUSINESS ADDRESS OF APPLICANT:
Reg. No. 9302735/06
10 Lindley Street
DATE OF PUBLICATION OF THIS PACKAGE INSERT:
8 February 1995
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