Brands, Medical Use, Clinical Data
- Cholinesterase Reactivators
Brands / Synonyms
Atnaa; Duodote; Pralidoxime Chloride; Protopam; Protopam Chloride
For the treatment of poisoning due to those pesticides and chemicals of the organophosphate class which have anticholinesterase activity and in the control of overdosage by anticholinesterase drugs used in the treatment of myasthenia gravis.
Pralidoxime is to reactivate cholinesterase (mainly outside of the central nervous system) which has been inactivated by phosphorylation due to an organophosphate pesticide or related compound. The destruction of accumulated acetylcholine can then proceed, and neuromuscular junctions will again function normally. Pralidoxime also slows the process of "aging" of phosphorylated cholinesterase to a nonreactivatable form, and detoxifies certain organophosphates by direct chemical reaction. The drug has its most critical effect in relieving paralysis of the muscles of respiration. Because pralidoxime is less effective in relieving depression of the respiratory center, atropine is always required concomitantly to block the effect of accumulated acetylcholine at this site. Pralidoxime relieves muscarinic signs and symptoms, salivation, bronchospasm, etc., but this action is relatively unimportant since atropine is adequate for this purpose.
Mechanism of Action
Pralidoxime is an antidote to organophosphate pesticides and chemicals. Organophosphates bind to the esteratic site of acetylcholinesterase, which results initially in reversible inactivation of the enzyme. If given within 24 hours,after organophosphate exposure, pralidoxime reactivates the enzyme cholinesterase by cleaving the phosphate-ester bond formed between the organophosphate and acetylcholinesterase.
Biotrnasformation / Drug Metabolism
There are no known absolute contraindications for the use of Protopam. Relative contraindications include known
hypersensitivity to the drug and other situations in which the risk of its use clearly outweighs possible
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.
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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.