Sodium nitroprusside

Sodium nitroprusside
IUPAC name Sodium pentacyanonitrosylferrate(II)
Other names Sodium nitroprusside Sodium nitroferricyanide Sodium pentacyanonitrosylferrate SNP
Identifiers
CAS number	14402-89-2 Y, (anhydrous) 13755-38-9 (dihydrate)
PubChem	26256
EC number	238-373-9
DrugBank	APRD01143
ChEMBL	CHEMBL1213351 N, CHEMBL74115
RTECS number	LJ8750000
ATC code	C02DD01
Properties
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
Structure
Coordination geometry	octahedral at Fe
Pharmacology
Routes of administration	Intravenous
Metabolism	Circulatory
Elimination half-life	2 minutes (metabolites: several days)
Excretion	Renal
Legal status	℞ Prescription only
Pregnancy category	C
Hazards
EU Index	Not listed
Flash point	Non-flammable
N (verify) (what is: Y/N?) 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. The sodium salt dissolves in water and to a lesser extent in ethanol to give solutions containing the dianion [Fe(CN)₅NO]²⁻.

Structure and properties

Nitroprusside is a complex anion that features an octahedral ferrous centre surrounded by five tightly bound cyanide ligands and one linear nitric oxide ligand. The molecular symmetry is C_4v. 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 are mainly associated with the NO ligand.^[2]

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

Medical pharmacology

Sodium nitroprusside (Abbreviated SNP, brand name: Nitropress) has potent vasodilating effects in arterioles and venules (arterioles more than venules). It is administered intravenously in cases of acute hypertensive emergency. SNP breaks down in circulation to release nitric oxide (NO). NO activates guanylate cyclase in vascular smooth muscle and increases intracellular production of cGMP. cGMP stimulates calcium movement from the cytoplasm to the endoplasmic reticulum and reduces calcium available to bind with calmodulin. Vascular smooth muscle relaxes, which allow vessels to dilate.

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.

Metabolism and toxicity

Sodium nitroprusside slowly breaks down to release 5 cyanide ions, especially upon exposure to UV light. Despite the toxic potential of cyanide, 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. 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.^[4] The half-life of nitroprusside is 1–2 minutes, but the metabolite thiocyanate has an excretion half-life of several days.

Use in research

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.

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. Colour change on the strip indicates the relative concentration of ketones.

Sodium nitroprusside spectrum is used to calibrate Mössbauer spectrometers

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 colour 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, also known as Brand's 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 colour 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 pathology in the transport of dibasic amino acids.

SNP is also used in microbiology, where it has been linked with the dispersal of Pseudomonas aeruginosa biofilms by acting as a nitric oxide donor.^[5]

References

1. ^ A. R. Butler, I. L. Megson (2002). "Non-Heme Iron Nitrosyls in Biology". Chemical Reviews 102 (4): 1155–1165. doi:10.1021/cr000076d. 
2. ^ Coppens, P.; Novozhilova, I.; Kovalevsky, A. (2002). "Photoinduced Linkage Isomers of Transition-Metal Nitrosyl Compounds and Related Complexes". Chem. Rev. 102 (4): 861–883. doi:10.1021/cr000031c. 
3. ^ A. Navaza, G. Chevrier, P. M. Alzari, P. J. Aymonino (1989). "Single-crystal neutron diffraction structure of sodium pentacyanonitrosylferrate(2−) (sodium nitroprusside) dihydrate". Acta Cryst. 45 (6): 839–841. doi:10.1107/S0108270188013691. 
4. ^ Nitropress (Nitroprusside Sodium) Drug Information: User Reviews, Side Effects, Drug Interactions and Dosage at RxList. Rxlist.com. Retrieved on 2010-12-11.
5. ^ Barraud, N; Hassett, DJ; Hwang, SH; Rice, SA; Kjelleberg, S; Webb, JS (2006). "Involvement of nitric oxide in biofilm dispersal of Pseudomonas aeruginosa". Journal of bacteriology 188 (21): 7344–53. doi:10.1128/JB.00779-06. PMC 1636254. PMID 17050922. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1636254.