C22H26NO6 = 399.21.
Colchicine, C22H25NO6, is an alkaloid found in colchicum corm, flowers, and seeds. It is official in the U.S.P. It occurs in the form of yellow flakes, or as a whitish-yellow amorphous powder, having a hay-like odour when damped and warmed, a very bitter taste, and darkening on exposure to light, owing to the formation of oxydicolchicine. The aqueous solution of colchicine is neutral to litmus, and laevorotatory. Melting-point, when dry, 142.5°. It is a feeble base and is decomposed when warmed with dilute acids or alkalies, methyl alcohol and colchicine being formed. It may be extracted from acid solution by chloroform. If a small quantity be dissolved in sulphuric acid, and a little nitric acid added, a greenish-blue colour is produced, which changes through sky-blue to red and yellow; on the addition of sodium hydroxide to the yellow solution it becomes red. Nitric acid produces with colchicine a dull violet colour, which passes to greenish, and finally to yellow. It should leave no residue on ignition. If 1 decigram be mixed with 3 decigrams of calcium carbonate, moistened with water, dried, and ignited, the residue, when dissolved in nitric acid, should be free from chlorides (absence of a compound of colchicine and chloroform). Colchicine should be kept in a dark place.
Soluble in water, alcohol, or chloroform; very slightly soluble in.ether; almost insoluble in petroleum ether.
Action and Uses.—Colchicine has a marked action upon plain muscle, especially of the intestine, producing increased peristalsis and setting up diarrhoea and vomiting. It is a slow poison to the brain; in large doses after a latent period of from one to three hours, a motor and sensory paralysis occurs, ending in death from respiratory failure. Colchicine undergoes change to oxydicolchicine in the system. It first decreases and then increases the proportion of leucocytes in the blood, and excites karyokinesis in bone marrow cells. Colchicine is employed as a specific in acute gout. Its action in gout may be due to its effect upon the white corpuscles or a corresponding stimulation of other tissues of the body. It has no effect on the heart and circulatory system. It is occasionally administered in the form of solution, but solutions do not keep well, and pills are better. These may be prepared with milk sugar and glycerin of tragacanth. The alkaloid is largely used in combination with methyl salicylate in capsules containing ¼ milligram.(1/250 grain) of the base or of colchicine salicylate. For hypodermic injection, a solution should be freshly prepared, containing 2 milligrams in 1 mil (1/32 grain in 15 minims). In cases of poisoning by colchicine, the antidotes described under colchicum corm should be employed.
Dose.—½ to 2 milligrams (1/120 to 1/30 grain).