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Pralidoxime Injection (Pralidoxime Chloride Injection) - Description and Clinical Pharmacology

 
 



PRALIDOXIME CHLORIDE INJECTION
(AUTO-INJECTOR)

FOR USE IN NERVE AGENT POISONING ONLY

A Sterile Solution For Intramuscular Use Only

Rx Only

DESCRIPTION

Pralidoxime Chloride Injection (auto-injector) provides pralidoxime chloride in a sterile solution for intramuscular injection.

Each prefilled auto-injector provides a dose of the antidote, pralidoxime chloride in a self-contained unit, specially designed for automatic self- or buddy- administration by military personnel. Pralidoxime in the auto-injector may also be administered by qualified civilian emergency responders who have had adequate training in the on-site recognition and treatment of nerve agent intoxication in the event of an accidental release of nerve agent. The recommended procedure (see DOSAGE AND ADMINISTRATION) is to inject the contents of the auto-injector into the muscles of an outer thigh.

After an auto-injector has been activated, the empty container should be disposed of properly (see DOSAGE AND ADMINISTRATION), it cannot be refilled nor can the protruding needle be retracted.

When activated, each auto-injector dispenses 600 mg of pralidoxime chloride in 2 mL of a sterile solution containing 20 mg/mL benzyl alcohol, 11.26 mg/mL glycine in Water for Injection, USP. The pH is adjusted with hydrochloric acid. The pH range is 2.0-3.0. The product is pyrogen free.

Pralidoxime chloride is a cholinesterase reactivator.

Chemical Name: 2-formyl-1 methylpyridinium chloride oxime (pyridine-2-aldoxime methochloride). Also referred to as 2-PAM Chloride.

Structural Formula:

Pralidoxime chloride occurs as an odorless, white, nonhygroscopic, crystalline powder which is soluble in water to the extent of 1 g in less than 1 mL.  Stable in air, it melts between 215°C and 225°C, with decomposition.

The specific activity of the drug resides in the 2-formyl-1 methylpyridinium ion and is independent of the particular salt employed. The chloride is preferred because of physiologic compatibility, excellent water solubility at all temperatures, and high potency per gram, due to its low (173) molecular weight.

CLINICAL PHARMACOLOGY

Pralidoxime chloride is a cholinesterase reactivator.

The principal action of 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 non-reactivatable 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.

Pralidoxime is distributed throughout the extracellular water, it is not bound to plasma protein. The drug is rapidly excreted in the urine partly unchanged, and partly as a metabolite produced by the liver. Consequently, pralidoxime is relatively short acting and repeated doses may be needed, especially where there is any evidence of continuing absorption of the poison.

The minimum therapeutic concentration of pralidoxime in plasma is 4 μ g/mL, this level is reached in about 16 minutes after a single injection of 600 mg pralidoxime chloride. The apparent half-life of pralidoxime chloride is 74-77 minutes.

It has been reported that the supplemental use of oxime cholinesterase reactivators (such as pralidoxime) reduces the incidence and severity of developmental defects in chick embryos exposed to such known teratogens as parathion, bidrin, carbachol and neostigmine. This protective effect of the oximes was shown to be dose related.

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