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Physostigmine (Physostigmine Salicylate) - Description and Clinical Pharmacology

 
 



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DESCRIPTION:

Physostigmine Salicylate Injection is a derivative of the Calabar bean, and its active moiety, physostigmine, is also known as eserine. Its chemical structure is:

It is soluble in water and a 0.5% aqueous solution has a pH of 5.8.

Physostigmine Salicylate Injection is available in 2 mL ampules, each mL containing 1 mg of Physostigmine Salicylate in a vehicle composed of sodium metabisulfite 0.1%, benzyl alcohol 2.0% as a preservative in Water for Injection.

CLINICAL PHARMACOLOGY:

Physostigmine Salicylate Injection is a reversible anticholinesterase which effectively increases the concentration of acetylcholine at the sites of cholinergic transmission. The action of acetylcholine is normally very transient because of its hydrolysis by the enzyme, acetylcholinesterase. Physostigmine Salicylate Injection inhibits the destructive action of acetylcholinesterase and thereby prolongs and exaggerates the effect of the acetylcholine.

Physostigmine Salicylate Injection contains a tertiary amine and easily penetrates the blood brain barrier, while an anticholinesterase, such as neostigmine, which has a quaternary ammonium ion is not capable of crossing the barrier. Physostigmine Salicylate Injection can reverse both central and peripheral anticholinergia. The anticholinergic syndrome has both central and peripheral signs and symptoms. Central toxic effects include anxiety, delirium, disorientation, hallucinations, hyperactivity and seizures. Severe poisoning may produce coma, medullary paralysis and death. Peripheral toxicity is characterized by tachycardia, hyperpyrexia, mydriasis, vasodilation, urinary retention, diminution of gastrointestinal motility, decrease of secretion in salivary and sweat glands, and loss of secretions in the pharynx, bronchi, and nasal passages.

Dramatic reversal of the effects of anticholinergic symptoms can be expected in minutes after the intravenous administration of Physostigmine Salicylate Injection, if the diagnosis is correct and the patient has not suffered anoxia or other insult. The duration of action of Physostigmine Salicylate Injection is relatively short, approximately 45 to 60 minutes.

Numerous drugs and some plants produce the anticholinergic syndrome either directly or as a side effect; this undesirable or potentially dangerous phenomenon may be brought about by either therapeutic doses or overdoses of the drugs. Such drugs include among others, atropine, other derivatives of the belladonna alkaloids, tricyclic antidepressants, phenothiazines, and antihistamines.

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