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# Sodium nitroprusside

An intravenous nitric oxide donor for hypertensive emergencies. It works within minutes but releases cyanide, so it needs close monitoring.

Updated 2026-11-01

- Class: [Direct vasodilators](https://durgical.com/en/pharmacology/classes/direct-vasodilators/)
- Enzyme: Soluble guanylyl cyclase (activated by the nitric oxide it releases)
- ATC code: C02DD01
- WHO Model List of Essential Medicines

## ⚠ High-alert medication

An error with this medicine can cause serious harm: double checks and protocols are used.

Also called: Nitroprusside

## Mechanism of action

Nitroprusside is an iron complex carrying cyanide groups and a nitroso group. In red cells it reacts with haemoglobin and releases nitric oxide, which activates soluble guanylyl cyclase in vascular smooth muscle; cGMP rises and both arteries and veins relax, lowering afterload and preload. The cyanide released is converted to thiocyanate by the mitochondrial enzyme rhodanese.

- Nitroprusside reacts with haemoglobin and releases nitric oxide
- Nitric oxide activates guanylyl cyclase; cGMP rises
- Arteries and veins relax: afterload and preload fall
- Released cyanide is converted to thiocyanate

## Pharmacokinetics

**Distribution**
Distributes in the extracellular space

**Metabolism**
Reaction with haemoglobin releases nitric oxide and cyanide; rhodanese turns cyanide into thiocyanate using thiosulfate

**Elimination**
Thiocyanate is cleared by the kidneys, with a half-life of about 3 days that lengthens in kidney failure (label)

**Onset and duration**
Within a minute or two; the effect fades almost as fast when the infusion stops (label)

## Indications

- Hypertensive crisis, for immediate reduction of blood pressure [Arterial hypertension →](https://durgical.com/en/conditions/arterial-hypertension/)
- Controlled hypotension to reduce bleeding during surgery
- Acute heart failure [Heart failure →](https://durgical.com/en/conditions/heart-failure/)

## Adverse effects

### Common

- Excessive hypotension
- Nausea, sweating and restlessness from a too-rapid fall in pressure
- Headache and palpitations
- Bradycardia or tachycardia

### Serious (rare, important)

- Cyanide toxicity: metabolic acidosis, bright red venous blood, confusion and death
- Thiocyanate toxicity, especially in kidney failure
- Methaemoglobinaemia
- Precipitous hypotension with ischaemic injury

## Contraindications

- Compensatory hypertension (aortic coarctation, arteriovenous shunting)
- Controlled hypotension in surgery with inadequate cerebral circulation or in moribund patients
- Congenital (Leber) optic atrophy or tobacco amblyopia
- Acute heart failure with reduced peripheral resistance, such as high-output failure in sepsis

## Key interactions

**Other antihypertensives**
Additive fall in blood pressure

**Ganglionic blockers and inhaled anaesthetics**
Stronger hypotensive effect

## What is monitored

- Continuous blood pressure (invasive is usual)
- Acid-base status, lactate and venous oxygen for cyanide toxicity
- Thiocyanate in long infusions or kidney failure
- Methaemoglobin if oxygen delivery seems impaired

## Administration and safety

- Not for direct injection: always diluted in a dextrose solution and given by infusion pump.
- Protect the bag from light with an opaque cover; the drip chamber and tubing do not need covering.
- The diluted solution has a faint brownish tint; discard it if it turns blue, green or bright red.
- No other drugs are added to or run in the same solution.
- Only where continuous blood pressure monitoring and trained staff are available.

## Nursing care

- Before: an arterial line and an infusion pump are ready; baseline acid-base status and kidney function.
- During: blood pressure continuously; a fall that is too fast can cause cerebral, cardiac or renal ischaemia.
- Watch for signs of cyanide toxicity: rising lactate, metabolic acidosis, confusion, air hunger.
- Watch for thiocyanate toxicity (tinnitus, miosis, hyperreflexia) in long infusions or kidney failure.
- A longer-acting oral antihypertensive is started so the infusion can be stopped as soon as possible.

## Pregnancy and breastfeeding

Nitroprusside crosses the placenta, and fetal cyanide levels follow maternal levels in animal studies; it is used in pregnancy only when the benefit clearly outweighs the risk.

## Memory aid

NitroPRUSSIDE: Powerful, Rapid, Unstable in light, Sensitive monitoring, Spits out cyanIDE.

## Test yourself

Think of the answer, then tap the question to see it.

## How does sodium nitroprusside relax vessels?

It releases nitric oxide, which activates soluble guanylyl cyclase; the rise in cGMP relaxes arterial and venous smooth muscle.

## Which toxicity limits long or high-rate nitroprusside infusions, and how does it show?

Cyanide toxicity: metabolic (lactic) acidosis, bright red venous blood (cells cannot extract oxygen), confusion and air hunger.

## Why is the infusion bag covered?

Nitroprusside is degraded by light, so the bag is protected with an opaque cover.

## Which metabolite accumulates in kidney failure during nitroprusside use?

Thiocyanate, which is cleared by the kidneys and causes tinnitus, miosis and hyperreflexia when it accumulates.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/sodium-nitroprusside/)

## Related drugs

- [Hydralazine](https://durgical.com/en/pharmacology/hydralazine/)
- [Minoxidil](https://durgical.com/en/pharmacology/minoxidil/)

## Related conditions

- [Arterial hypertension](https://durgical.com/en/conditions/arterial-hypertension/)
- [Heart failure](https://durgical.com/en/conditions/heart-failure/)

[← Back to the class: Direct vasodilators](https://durgical.com/en/pharmacology/classes/direct-vasodilators/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [DailyMed - SODIUM NITROPRUSSIDE injection, solution, concentrate](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6fbfb86c-da8d-4741-b1e0-7000e2bbad5f) (DailyMed (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=C02DD01) (WHO Collaborating Centre for Drug Statistics Methodology, 2026); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/) (World Health Organization, 2025); Farmacología básica y clínica (Katzung), cap. 11 (McGraw Hill, 2025).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/sodium-nitroprusside/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/sodium-nitroprusside/