Pralidoxime

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Pralidoxime
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Clinical data
Other names1-methylpyridine-6-carbaldehyde oxime
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  • C
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  • In general: ℞ (Prescription only)
Identifiers
  • 2-[(hydroxyimino)methyl]-1-methylpyridin-1-ium
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Chemical and physical data
Formula C7H9N2O+
Molar mass 137.162 g·mol−1
3D model (JSmol)
  • ON=Cc1cccc[n+]1C
  • InChI=1S/C7H8N2O/c1-9-5-3-2-4-7(9)6-8-10/h2-6H,1H3/p+1 Yes check.svgY
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Pralidoxime (2-pyridine aldoxime methyl chloride) or 2-PAM, usually as the chloride or iodide salts, belongs to a family of compounds called oximes that bind to organophosphate-inactivated acetylcholinesterase. [1] It is used to treat organophosphate poisoning [2] in conjunction with atropine and either diazepam or midazolam. It is a white solid.

Contents

Chemical synthesis

Pralidoxime, 2-pyridinaldoxime methylchloride, is prepared by treating pyridine-2-carboxaldehyde with hydroxylamine. The resulting pyridine-2-aldoxime is alkylated with methyl iodide giving pralidoxime as the iodide salt. [3] [4] [5] [6]

Pralidoxime synthesis.png

Mechanism of action

Pralidoxime is typically used in cases of organophosphate poisoning. Organophosphates such as sarin bind to the hydroxy component (the esteric site) of the active site of the acetylcholinesterase enzyme, thereby blocking its activity. Pralidoxime binds to the other half (the unblocked, anionic site) of the active site and then displaces the phosphate from the serine residue. The conjoined poison / antidote then unbinds from the site, and thus regenerates the fully functional enzyme.

Some phosphate-acetylcholinesterase conjugates continue to react after the phosphate docks to the esteric site, evolving into a more recalcitrant state. This process is known as aging. Aged phosphate-acetylcholinesterase conjugate are resistant to antidotes such as pralidoxime. Pralidoxime is often used with atropine (a muscarinic antagonist) to help reduce the parasympathetic effects of organophosphate poisoning. Pralidoxime is only effective in organophosphate toxicity. It has no beneficial effects if the acetylcholinesterase enzyme is carbamylated, as occurs with neostigmine, pyridostigmine, or insecticides such as carbaryl.

Pralidoxime has an important role in reversing paralysis of the respiratory muscles but due to its poor blood–brain barrier penetration, it has little effect on centrally-mediated respiratory depression. Atropine, which is choice of drug to antagonise the muscarinic effects of organophosphates, is administered even before pralidoxime during the treatment of organophosphate poisoning. While the efficacy of atropine has been well-established, clinical experience with pralidoxime has led to widespread doubt about its efficacy in treatment of organophosphorus poisoning. [7]

Dosage

Intravenous infusions can lead to respiratory or cardiac arrest if given too quickly. [8]

Interactions

When atropine and pralidoxime are used together, the signs of atropinization (flushing, mydriasis, tachycardia, dryness of the mouth and nose) may occur earlier than might be expected when atropine is used alone. This is especially true if the total dose of atropine has been large and the administration of pralidoxime has been delayed.

The following precautions should be kept in mind in the treatment of anticholinesterase poisoning, although they do not bear directly on the use of pralidoxime: since barbiturates are potentiated by the anticholinesterases, they should be used cautiously in the treatment of convulsions; morphine, theophylline, aminophylline, succinylcholine, reserpine, and phenothiazine-type tranquilizers should be avoided in patients with organophosphate poisoning.

Contraindications

There are no known absolute contraindications for the use of pralidoxime. Relative contraindications include known hypersensitivity to the drug and other situations in which the risk of its use clearly outweighs possible benefit.

See also

Related Research Articles

Nerve agents, sometimes also called nerve gases, are a class of organic chemicals that disrupt the mechanisms by which nerves transfer messages to organs. The disruption is caused by the blocking of acetylcholinesterase (AChE), an enzyme that catalyzes the breakdown of acetylcholine, a neurotransmitter. Nerve agents are acetylcholinesterase inhibitors used as poison.

<span class="mw-page-title-main">Soman</span> Chemical compound (nerve agent)

Soman is an extremely toxic chemical substance. It is a nerve agent, interfering with normal functioning of the mammalian nervous system by inhibiting the enzyme cholinesterase. It is an inhibitor of both acetylcholinesterase and butyrylcholinesterase. As a chemical weapon, it is classified as a weapon of mass destruction by the United Nations according to UN Resolution 687. Its production is strictly controlled, and stockpiling is outlawed by the Chemical Weapons Convention of 1993 where it is classified as a Schedule 1 substance. Soman was the third of the so-called G-series nerve agents to be discovered along with GA (tabun), GB (sarin), and GF (cyclosarin).

<span class="mw-page-title-main">Atropine</span> Tropane alkaloid anticholinergic medication & used as antidote for nerve agent poisoning

Atropine is a tropane alkaloid and anticholinergic medication used to treat certain types of nerve agent and pesticide poisonings as well as some types of slow heart rate, and to decrease saliva production during surgery. It is typically given intravenously or by injection into a muscle. Eye drops are also available which are used to treat uveitis and early amblyopia. The intravenous solution usually begins working within a minute and lasts half an hour to an hour. Large doses may be required to treat some poisonings.

<span class="mw-page-title-main">Cholinesterase</span> Esterase that lyses choline-based esters

The enzyme cholinesterase (EC 3.1.1.8, choline esterase; systematic name acylcholine acylhydrolase) catalyses the hydrolysis of choline-based esters:

<span class="mw-page-title-main">Chlorfenvinphos</span> Chemical compound

Chlorfenvinphos is the common name of an organophosphorus compound that was widely used as an insecticide and an acaricide. The molecule itself can be described as an enol ester derived from dichloroacetophenone and diethylphosphonic acid. Chlorfenvinphos has been included in many products since its first use in 1963. However, because of its toxic effect as a cholinesterase inhibitor it has been banned in several countries, including the United States and the European Union. Its use in the United States was cancelled in 1991.

Obidoxime is a member of the oxime family used to treat nerve gas poisoning. Oximes are drugs known for their ability to reverse the binding of organophosphorus compounds to the enzyme acetylcholinesterase (AChE).

<span class="mw-page-title-main">Azinphos-methyl</span> Chemical compound

Azinphos-methyl (Guthion) is a broad spectrum organophosphate insecticide manufactured by Bayer CropScience, Gowan Co., and Makhteshim Agan. Like other pesticides in this class, it owes its insecticidal properties to the fact that it is an acetylcholinesterase inhibitor. It is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S. Emergency Planning and Community Right-to-Know Act, and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.

<span class="mw-page-title-main">Phosmet</span> Organophosphate non-systemic insecticide

Phosmet is a phthalimide-derived, non-systemic, organophosphate insecticide used on plants and animals. It is mainly used on apple trees for control of codling moth, though it is also used on a wide range of fruit crops, ornamentals, and vines for the control of aphids, suckers, mites, and fruit flies.

<span class="mw-page-title-main">Organophosphate poisoning</span> Medical condition

Organophosphate poisoning is poisoning due to organophosphates (OPs). Organophosphates are used as insecticides, medications, and nerve agents. Symptoms include increased saliva and tear production, diarrhea, vomiting, small pupils, sweating, muscle tremors, and confusion. While onset of symptoms is often within minutes to hours, some symptoms can take weeks to appear. Symptoms can last for days to weeks.

<span class="mw-page-title-main">Chlorethoxyfos</span> Chemical compound

Chlorethoxyfos is an organophosphate acetylcholinesterase inhibitor used as an insecticide. It is registered for the control of corn rootworms, wireworms, cutworms, seed corn maggot, white grubs and symphylans on corn. The insecticide is sold under the trade name Fortress by E.I. du Pont de Nemours & Company.

<span class="mw-page-title-main">Disulfoton</span> Chemical compound

Disulfoton is an organophosphate acetylcholinesterase inhibitor used as an insecticide. It is manufactured under the name Di-Syston by Bayer CropScience. Disulfoton in its pure form is a colorless oil but the technical product used in vegetable fields is dark and yellowish with a sulfur odor. Disulfoton is processed as a liquid into carrier granules, these granules are mixed with fertilizer and clay to be made into a spike, designed to be driven into the ground. The pesticide is absorbed over time by the roots and translocated to all parts of the plant. The pesticide acts as a cholinesterase inhibitor and gives long lasting control.

An ATNAA is any of a variety of autoinjectors in use with the US Armed Forces. An autoinjector is a medical device designed to deliver a single dose of a particular drug.

<span class="mw-page-title-main">Acetylcholinesterase inhibitor</span> Drugs that inhibit acetylcholinesterase

Acetylcholinesterase inhibitors (AChEIs) also often called cholinesterase inhibitors, inhibit the enzyme acetylcholinesterase from breaking down the neurotransmitter acetylcholine into choline and acetate, thereby increasing both the level and duration of action of acetylcholine in the central nervous system, autonomic ganglia and neuromuscular junctions, which are rich in acetylcholine receptors. Acetylcholinesterase inhibitors are one of two types of cholinesterase inhibitors; the other being butyryl-cholinesterase inhibitors. Acetylcholinesterase is the primary member of the cholinesterase enzyme family.

<span class="mw-page-title-main">Cholinesterase inhibitor</span> Chemicals which prevent breakdown of acetylcholine and butyrylcholine

Cholinesterase inhibitors (ChEIs), also known as anti-cholinesterase, are chemicals that prevent the breakdown of the neurotransmitter acetylcholine or butyrylcholine. This increases the amount of the acetylcholine or butyrylcholine in the synaptic cleft that can bind to muscarinic receptors, nicotinic receptors and others. This group of inhibitors is divided into two subgroups, acetylcholinesterase inhibitors (AChEIs) and butyrylcholinesterase inhibitors (BChEIs).

<span class="mw-page-title-main">Tetraethyl pyrophosphate</span> Chemical compound

Tetraethyl pyrophosphate, abbreviated TEPP, is an organophosphate compound with the formula [(C2H5O)2P(O)]2O. It is the tetraethyl derivative of pyrophosphate (P2O74-). It is a colorless oil that solidifies near room temperature. It is used as an insecticide. The compound hydrolyzes rapidly.

<span class="mw-page-title-main">Terbufos</span> Chemical compound

Terbufos is a chemical compound used in insecticides and nematicides. Terbufos is part of the chemical family of organophosphates. It is a clear, colourless to pale yellow or reddish-brown liquid and sold commercially as granulate.

<span class="mw-page-title-main">Triazofos</span> Chemical compound

Triazofos is a chemical compound used in acaricides, insecticides, and nematicides.

<span class="mw-page-title-main">Crotylsarin</span> Chemical compound

Crotylsarin (CRS) is an extremely toxic organophosphate nerve agent of the G-series. Like other nerve agents, CRS irreversibly inhibits the acetylcholinesterase. However, since the inhibited enzyme ages so rapidly, the inhibited enzyme can't be reactivated by cholinesterase reactivators.

<span class="mw-page-title-main">Guanitoxin</span> Chemical compound

Guanitoxin (GNT), formerly known as anatoxin-a(S) "Salivary", is a naturally occurring cyanotoxin commonly isolated from cyanobacteria and causes excess salivation in mammals via inhibition of acetylcholinesterase. Guanitoxin was first structurally characterized in 1989, and consists of a cyclic N-hydroxyguanine organophosphate with a phosphate ester moiety.

Cholinesterase reactivators are drugs that reverses the inhibition of cholinesterase by organophosphates or sulfonates. They are used as antidote for treating organophosphate insecticide and nerve agent poisoning.

References

  1. Jokanović M, Stojiljković MP (December 2006). "Current understanding of the application of pyridinium oximes as cholinesterase reactivators in treatment of organophosphate poisoning". European Journal of Pharmacology. 553 (1–3): 10–7. doi:10.1016/j.ejphar.2006.09.054. PMID   17109842.
  2. Jokanović M, Prostran M (2009). "Pyridinium oximes as cholinesterase reactivators. Structure-activity relationship and efficacy in the treatment of poisoning with organophosphorus compounds". Current Medicinal Chemistry. 16 (17): 2177–88. doi:10.2174/092986709788612729. PMID   19519385.
  3. US 2816113,Nachmansonn E, Ginsburg S,published 1957
  4. US 3123613,Black LP,published 1964
  5. US 3140289,Easterday DE, Kondritzer AA,published 1964
  6. US 3155674,McDowell WB,published 1964
  7. Banerjee I, Tripathi SK, Roy AS (2014). "Efficacy of pralidoxime in organophosphorus poisoning: revisiting the controversy in Indian setting". Journal of Postgraduate Medicine. 60 (1): 27–30. doi: 10.4103/0022-3859.128803 . PMID   24625936.
  8. Baxter Healthcare Corporation 2006, Protopam Prescribing Information