PHYSIOSTIGMINE

PHYSIOSTIGMINE




Brad Names : Eserine; Physostol.

Physostigmine. m.p. 105-106°. is an alkaloid obtained from the calabar bean (ordeal beam, chopnut), the seed of Physostigma venenosum (Leguminosae). 




It occurs as a white, odourless, microcrystalline powder which becomes pink on exposure to heat, light, air, or contact with traces of metals. It is slightly soluble in water; very soluble in chloroform; freely soluble in alcohol; soluble in fixed oils. Under certain conditions the oxidation may proceed to yield eserine blue. The compound is stored in airtight containers and protected from light.

Physostigmine salicylate is prepared by neutralizing an ethereal solution of the alkaloid with an ethereal solution of salicylic acid. Excess salicylic acid is removed from the precipitated product by washing it with ether.

The salicylate, m.p. 185-187, is a colourless, shining odourless crystalline material or white powder; soluble in water, alcohol orchloroform; slightly soluble in ether. The crystals and their aqueous solutions become red on exposure to heat, light, air and contact with traces of metals. The red solutions are not effective. Therefore, solutions should be kept well closed in light-resistant, alkali-free glass containers and used within a week .


Physostigmine sulphate, m.p. 140°, is a white, deliquescent, odourless, microcrystalline powder; soluble in alcohol and water; slightly soluble in ether. The powder and its aqueous solution become red on exposure to heat, light, air and contact with traces of metals. The red colour may be removed by washing the crystals with alcohol.


The degradation products of physostigmine are eseroline, red coloured compound rubreserine, eserine blue, and esernine brown. The oxidation of eserinol (a phenol) may be prevented by adding sodium sulphite and no red colour will be formed. In solution, physostigmine is first hydrolyzes to methylcarbamic acid and eserinol which is oxidized rapidly to rubreserine. Solutions are most stable at pH 6 and they should not be sterilized by heat. Physostigmine is stabilized up to 6 months on addition of ascorbic acid.

Uses :



 Physostigmine is cholinergic (anticholinesterase) and used as a miotic, to counteract the dilation of the pupil caused by atropine, homatropine, or cocaine and to decrease intraocular pressure in glaucoma.




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