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Sodium nitroprusside
Sample of sodium nitroprusside
Sodium nitroprusside
IUPAC name
Other names Sodium nitroprusside
Sodium nitroferricyanide
Sodium pentacyanonitrosylferrate
CAS number 14402-89-2 Yes check.svgY,(anhydrous)
13755-38-9 (dihydrate)
PubChem 26256
EC number 238-373-9
DrugBank APRD01143
RTECS number LJ8750000
ATC code C02DD01
Molecular formula Na2[Fe(CN)5NO]
Molar mass 261.92 g/mol (anhydrous)
297.95 g/mol (dihydrate)
Appearance red powder
Solubility in water good
Solubility in ethanol soluble
octahedral at Fe
Routes of
Metabolism Circulatory
2 minutes (metabolites: several days)
Excretion Renal
Legal status

Prescription only

EU Index Not listed
Flash point Non-flammable
 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Sodium nitroprusside is the inorganic compound with the formula Na2[Fe(CN)5NO]·2H2O.[1] This red-coloured salt, which is often abbreviated SNP, is a potent vasodilator.



"Nitroprusside" is an anion that features octahedral ferrous center surrounded by five tightly bound cyanide ligands and one linear nitric oxide ligand. The molecular symmetry is C4v. Linear nitrosyl ligands are assigned a single positive charge, thus the iron is assigned an oxidation state of 2+. As such it has a low-spin d6 electron configuration and is diamagnetic. Its chemical reactions have been studied widely.[2]

The sodium salt dissolves in water and to a lesser extent in ethanol to give a solution containing the dianion [Fe(CN)5NO]2−. This metal nitrosyl complex is the active agent in medical applications.

Ball-and-stick model of part of the crystal structure of sodium nitroprusside dihydrate
Ball-and-stick model of part of the crystal structure of sodium nitroprusside dihydrate[3]

Medical applications

Sodium nitroprusside is a common medication used to affect peripheral vasodilation in arterioles and venules (venules more than arterioles). Sodium nitroprusside is often administered intravenously to patients who are experiencing a hypertensive emergency.

In the bloodstream sodium nitroprusside decomposes to release nitric oxide (NO), which causes relaxation of vascular smooth muscle. In the human heart, nitric oxide reduces both total peripheral resistance as well as venous return, thus decreasing both preload and afterload. For this reason, it can be used in severe cardiogenic 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.

Sodium nitroprusside slowly breaks down to release cyanide when it is exposed to light. Normal physiological conditions within the human body also degrade the compound into cyanide. But despite its toxic potential, nitroprusside remains an effective drug in certain clinical circumstances such as malignant hypertension or for rapid control of blood pressure during vascular surgery and neurosurgery. By the action of the enzyme rhodanase, the cyanide can be detoxified by reaction with a sulfur donor such as thiosulfate. In the absence of sufficient thiosulfate, cyanide ions can quickly reach toxic levels.[4] The half-life of nitroprusside is 1–2 minutes although thiocyanate has an excretion half life of several days. The duration of treatment should not exceed 72 hours and thiocyanate plasma concentrations should be monitored.

In physiology research, sodium nitroprusside is frequently used to test endothelium-independent vasodilation. Iontophoresis, for example, allows local administration of the drug, preventing the systemic effects listed above but still inducing local microvascular vasodilation. Nitric oxide liberated from the sodium nitroprusside diffuses into the vascular smooth muscle causing relaxation and subsequent vasodilatation. This vasodilatation is quantified by various techniques. This role in the treatment of hypertension was first performed at the Cleveland Clinic. [5].

Sodium nitroprusside is also used in the presence of buffers as a reagent for ketone strips, which test the ketone levels in the urine of a diabetic. Color change on the strip indicates the relative concentration of ketones.

Other applications

Sodium nitroprusside is often used as a reference compound for the calibration of Mössbauer spectrometer. It is also used as an analytical reagent in qualitative organic analysis.

In combination with acetaldehyde it is also used as a color reagent in the development of thin layer chromtography plates, particularly for N-heterocyclic compounds.

Sodium nitroprusside is also used in a urinalysis test, called the cyanide nitroprusside test. In this test sodium cyanide is added first to urine and let stand for approximately 10 minutes. In this time disulfide bonds will be broken by the released cyanide. The destruction of disulfide bonds liberates cysteine from cystine and homocysteine from homocystine. Next sodium nitroprusside is added to the solution and it reacts with the newly freed sulfhydryl groups. The test will turn a red/purple color if the test is positive indicating that there was significant amounts of amino acid in the urine (aminoaciduria). Cysteine, cystine, homocysteine and homocystine all react when present in the urine when this test is performed. This test can indicate inborn errors of amino acid transporters such as cystinuria, which results from dibasic amino acid transport pathology.


  1. ^ A. R. Butler, I. L. Megson (2002). "Non-Heme Iron Nitrosyls in Biology". Chemical Reviews 102: 1155–1165. doi:10.1021/cr000076d.  
  2. ^ Coppens, P.; Novozhilova, I.; Kovalevsky, A. "Photoinduced Linkage Isomers of Transition-Metal Nitrosyl Compounds and Related Complexes" Chemical Reviews 2002, volume 102, pp.861-883.doi:10.1021/cr000031c
  3. ^ A. Navaza, G. Chevrier, P. M. Alzari, P. J. Aymonino (June 1989). "Single-crystal neutron diffraction structure of sodium pentacyanonitrosylferrate(2−) (sodium nitroprusside) dihydrate". Acta Cryst. 45 (6): 839–841. doi:10.1107/S0108270188013691.  
  4. ^
  5. ^

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