Its use in hepatically impaired individuals is also not recommended, as is its use in cases of pre-existing hypothyroidism.Its use in pregnant women is advised against, although the available evidence suggests it may be safe, provided maternal pH and cyanide levels are closely monitored. Some evidence suggests sodium nitroprusside use in critically ill children may be safe, even without monitoring of cyanide level. Interactions
The only known drug interactions are pharmacodynamic in nature, that is it is possible for other antihypertensive drugs to reduce the threshold for dangerous hypotensive effects to be seen. Overdose
Due to its cyanogenic nature, overdose may be particularly dangerous. Treatment of sodium nitroprusside overdose includes the following:
Discontinuing sodium nitroprusside administration
Buffering the cyanide by using sodium nitrite to convert haemoglobin to methaemoglobin as much as the patient can safely tolerate
Infusing sodium thiosulfate to convert the cyanide to thiocyanate.Haemodialysis is ineffective for removing cyanide from the body but it can be used to remove most of the thiocyanate produced from the above procedure. Toxicology
The cyanide can be detoxified by reaction with a sulfur-donor such as thiosulfate, catalysed by the enzyme rhodanese. In the absence of sufficient thiosulfate, cyanide ions can quickly reach toxic levels. Hydroxocobalamin can be administered to reduce the risk of thiocyanate toxicity induced by nitroprusside. Mechanism of action
As a result of its breakdown to nitric oxide (NO), sodium nitroprusside has potent vasodilating effects on arterioles and venules (arterial more than venous), whereas other nitrates exhibit more selectivity for veins (e.g. nitroglycerin).Sodium nitroprusside breaks down in circulation to release nitric oxide (NO).
So, it can be used in severe congestive heart failure where this combination of effects can act to increase cardiac output. In situations where cardiac output is normal, the effect is to reduce blood pressure. It is sometimes also used to induce hypotension (to reduce bleeding) for surgical procedures (for which it is also FDA, TGA, and MHRA labelled).The medication is extremely beneficial for use in medical patients because the effects of the medication will directly stop the second that it stops being infused. This is due to the metabolism of the drug, and the rapid inactivation to thiocyanin once conversion of the drug stops. This compound has also been used as a treatment for aortic valve stenosis, oesophageal varices, myocardial infarction, pulmonary hypertension, respiratory distress syndrome in the newborn, shock, and ergot toxicity. Adverse effects
Adverse effects by incidence and severityCommon

Unknown frequency

Serious

Ileus
Reduced platelet aggregation
Haemorrhage
Increased intracranial pressure
Metabolic acidosis
Methaemoglobinaemia
Cyanide poisoning
Thiocyanate toxicity

Contraindications
Sodium nitroprusside should not be used for compensatory hypertension (e.g. due to an arteriovenous stent or coarctation of the aorta). It should not be used in patients with inadequate cerebral circulation or in patients who are near death. It should not be used in patients with vitamin B12 deficiency, anaemia, severe renal disease, or hypovolaemia. Patients with conditions associated with a higher cyanide/thiocyanate ratio (e.g. congenital (Lebers) optic atrophy, tobacco amblyopia) should only be treated with sodium nitroprusside with great caution. Its use in patients with acute congestive heart failure associated with reduced peripheral resistance is also not recommended.