This section is from the "A Handbook of Useful Drugs" book, by State Medical Examining and Licensing Boards.
An alkaloid obtained from several varieties of Coca.
Properties : Cocain forms large colorless prisms, having a slightly bitter taste and producing on the tongue a temporary numbness. It is only slightly soluble in water (1 : 600), soluble in alcohol (1 :5), and also soluble in fixed oils, but insoluble in petrolatum and lard. The hydrochlorid is freely soluble in water.
Incompatibilities: Solutions of cocain or of any of its salts after being kept a long time, or on boiling, are hydrolyzed more or less completely into ecgonin, benzoic acid and methyl alcohol. Solutions of cocain cannot be sterilized by boiling without some loss, but the amount of decomposition is so small as to be insignificant.
Action and Uses : Cocain paralyzes the peripheral nerves when applied locally, causing loss of sensation, and also contracts the blood-vessels. The mucous membrane becomes pale from local constriction of the vessels. When injected into a nerve or around the nerve sheath, anesthesia of the region to which the sensory fibers of the nerve are distributed is produced. By injecting a solution of cocain into the spinal canal anesthesia of the greater part of the body can be produced, but this method has often resulted in serious accidents or fatalities and is not to be recommended, despite the reported successful use by individuals who have become expert in recognizing and combating untoward symptoms.
Cocain produces first stimulation and then depression of the different segments of the central nervous system, beginning with the brain and extending to the spinal cord and the medulla. The stimulation of the brain has generally passed into depression before that of the spinal cord has begun so that when considerable doses have been given the symptoms may consist of a mixture of stimulation and depression. Stimulation of the brain is shown by increased psychic activity, loss of sense of fatigue, insomnia and muscular irritability. Depression is shown by somnolence, stupor and finally coma.
Convulsions frequently occur owing to cerebral action.
Respiration is at first quickened, it may have a Cheyne-Stokes character and later symptoms of respiratory paralysis appear. The heart may be temporarily stimulated, but is later paralyzed. The pulse is accelerated by nervous stimulation. The blood-pressure is raised by small doses but later falls from vasomotor paralysis. The temperature may be increased by cocain.
Cocain is a mydriatic acting both locally and centrally. The dilatation is not so complete as that produced by atropin, and reaction to light is not abolished.
The therapeutic use of cocain is derived almost exclusively from its anesthetic properties. It is much used to secure bloodlessness and anesthesia of the mucous membranes of the conjunctiva, nose and pharynx. In the eye it is said to increase the action of other alkaloids. It has an injurious action on the cornea in certain cases, producing desquamation of the epithelium and causing a keratitis. It is said that the danger of such injury can be minimized by closing the eyes for some time after cocain instillations. A moist compress may also be applied when strong solutions are used. The possible danger of absorption of the drug from the conjunctiva should not be forgotten. Cocain may be used as an anesthetic in operations on the eye and is considered better than any of its substitutes by many ophthalmologists.
In the nose cocain is used for astringent purposes in early stages of coryza and other inflammations in which it renders nose breathing easier by reducing the swelling of the turbinated bodies. It is also employed for the checking of hemorrhage. For anesthetic purposes it is advantageously combined with solution of an epinephrin salt. Hemorrhage of capillary origin is particularly amenable to the use of cocain.
The painful deglutition and other inconveniences of laryngeal tuberculosis may be alleviated by local applications of cocain solutions to the ulcerated areas. A more effectual method is the injection of cocain solution into the sheath of the superior laryngeal nerve. Cocain has been much used by local application to. the nasal mucous membrane or by insufflation for the relief of asthma. Swabbing the pharynx with a solution of cocain is sometimes employed to facilitate the swallowing of the stomach tube. Such an application, however, is seldom needed.
Cocain has been employed as an antiemetic when vomiting depends on local irritation, but it should not be used for this purpose. It may be applied as a local anesthetic to hemorrhoids, but should be used with caution.
Dosage: For internal use the dose is 0.03 gm. or 1/2 grain. As a local application to mucous membranes it is usually employed in the form of cocain hydrochlorid in a solution of the strength of from 2 to 10 per cent., the average being about 4 per cent. In the stronger solutions it should be used cautiously for fear of poisoning from the alkaloid absorbed. In the vagina and rectum 10 per cent, solutions may be used, but it is not safe to use solutions stronger than from 1 to 2 per cent, in the urethra.