This section is from the book "Dental Medicine. A Manual Of Dental Materia Medica And Therapeutics", by Ferdinand J. S. Gorgas. Also available from Amazon: Dental Medicine.
Eucaine is an artificial alkaloid produced by the reaction between acetone (dimethyl ketone, Ch3coch3), and ammonia. Two chemical substances having the name of Eucaine have been introduced, each of them depending for its anaesthetic property upon the presence of the benzoyl molecule in its constitution. They are called, Alpha-Eucaine and Beta-Eucaine. Although Alpha-Eucaine was the substance usually sold under the name of Eucaine, yet it is as poisonous as cocaine, while Beta-Cocaine is not, cocaine being three times more toxic. The use of Alpha-Cocaine has been almost entirely discontinued. The salt principally employed is the hydrochlorate which, when evaporated from the aqueous solution, retains one molecule of water of crystallization.
Eucaine, when applied locally', induces some hyperemia of the mucosae, rather than anemia, but, nevertheless, causes a very decided loss of sensibility. It has a marked advantage over cocaine in being less poisonous, although their dosages are very similar. Lethal doses cause excitation of the central nervous system, convulsions affecting all the muscles, general paralysis, and death by a failure of the respiration. There is no ischemia due to contraction of the blood vessels, as in cocaine anaesthesia, and no paralysis of accommodation. According to Prof. Hare, however, eucaine is capable of producing internal effects resembling an over-dose of cocaine, which must be treated by the use of strong coffee, alcohol, digitalis and strychnine. If the case is pressing, ether, ammonia and nitro-glycerine may be used as rapidly acting stimulants. Solutions of eucaine hydro-chlorate (one part to ten parts of sterilized water) remain permanently unchanged, and boiling will not produce decomposition, which is another advantage over solutions of cocaine hydro-chlorate. This immunity is supposed to be due to its immediate derivation from pure chemicals, instead of from vegetable sources. The local effect of eucaine hydrochlorate upon the circulation is the production of hyperemia, whereas that of cocaine is ischemia. Eucaine also exalts the nervous system, when paralysis follows, the effect being central, causing acceleration of the heart-beats through sedation of the pneumogastric nerve. Experiments made by Dr. A. H. Peck lead him to conclude that the action of cocaine is inconstant, while those of eucaine are constant; that the first action on the heart and respiration of eucaine is that of a stimulant, the after-effects being that of a decided depressant; that eucaine causes death in animals by paralyzing the muscles of the heart and of the respiratory apparatus, they ceasing to operate simultaneously, while cocaine causes death by paralyzing the muscles of the respiratory apparatus, the heart's action continuing in a feeble way for a brief period after breathing ceases; that eucaine in toxic doses nearly always causes nausea, and occasionally vomiting, while cocaine is much less nauseating and scarcely ever causes vomiting; that cocaine is at least three times more toxic than Beta-Eucaine, and that Alpha-Eucaine is as toxic as cocaine. Eucaine solutions should be prepared with distilled or sterilized water, and then brought to the boiling point. All solutions should be freshly prepared to obtain the positive results. Dental Uses. - Beta-eucaine is employed in dental practice as a local anaesthetic. A ten per cent. solution may be made by adding 48 grains of beta-eucaine to the ounce of distilled water, and the solution brought to the boiling point. Of such a solution (10 per cent.) five to eight minims is a proper dose by hypodermic injection. Some recommend an eight per cent. solution as strong enough for the painless extraction of teeth. The mode of application and the precautions to be observed in employing such a solution in the extraction of teeth, are similar to those for the administration of cocaine solutions.
Eucaine solution is also serviceable in capping crowns of teeth, inserting bridge-work, and applying clamps in connection with the rubber dam, especially when the gums are tender and bleeding ; also for hypersensitive dentine, especially by the cataphoric method. (See Vapocaine.)