Caffeina Citrata (U. S. P.)—Citrated Caffeine.
SYNONYM: Caffeine citrate.
Preparation.—"Caffeine, fifty grammes, (50 Gm.) [1 oz. av., 334 grs.]; citric acid, fifty grammes (50 Gm.) [1 oz. av., 334 grs]; distilled water (hot) one hundred cubic centimeters (100 Cc.) [3 fl℥, 183♏]. Dissolve the citric acid in the hot distilled water, add the caffeine, and evaporate the resulting solution, on a waterbath, to dryness, constantly stirring towards the end of the operation. Reduce the product to a fine powder, and transfer it to well-closed bottles"—(U. S. P.).
Commercial citrate of caffeine, so-called, is not a definite salt, but as the pharmacopoeial. name (citrated caffeine) would indicate, it is the alkaloid caffeine, with a portion of adherent citric acid, as shown by Hager and Haarmann. While the process above given produces a citrated caffeine only, Prof. J. U. Lloyd has shown that a true citrate of caffeine may be obtained by dissolving caffeine in chloroform and citric acid in alcohol, and mixing the two solutions, when, by evaporation, crystals of caffeine citrate result. He has further shown that this salt, so obtained, decomposes immediately in contact with water. (See New Remedies, 1881, p. 38).
Description.—"A white powder, odorless, having a purely acid taste and an acid reaction. One part of citrated caffeine forms a clear, syrupy solution, with about 3 parts of water. Upon dilution with water, this yields a white precipitate (caffeine), which redissolves when about 25 parts of water have been added. It is also soluble in a mixture of 2 volumes of chloroform and 1 volume of alcohol"—(U. S. P.).
Action, Medical Uses, and Dosage.—The general action and uses of this drug are the same as those given under caffeine. This salt is used chiefly as a remedy for the idiopathic headache, called migraine (pain in the forehead). This salt is very soluble in water, and is assimilated much more readily than pure caffeine when taken into the stomach. It may be made into a pill mass with some simple extract, say 8 grains of the salt to 15 of the extract, and divided into 10 pills, of which 1 may be given every 1 or 2 hours. Pills, however, are not as desirable as other forms for administration. Or, 2 1/2 drachms of the salt may be dissolved in 4 ounces of simple syrup, of which 1 tablespoonful may be given as above, according to the violence of the attack. The dose of citrated caffeine ranges from 3 to 8 grains (see Caffeina for Uses and Specific Indications).
Related Salts of Caffeine.—VALERIANATE OF CAFFEINE. Like the citrated caffeine, this is not a definite product, and is liable to great variability in strength and quality. It has been employed in 1/3 to 1/2-grain doses, administered twice daily, for the relief of pertussis. It is asserted to be useful in allaying the vomiting hysteria.
CAFFEINE DIIODIDE-HYDRO-IODIDE (2C8H10N4O2I2HI+3H2O) or so-called caffeine triiodide, occurs as long prismatic crystals, of a deep-green color. It is freely dissolved by alcohol. Dose, 1 to 4 grains.
CAFFEINAE SODIO-BENZOAS (N.F.), Caffeine sodio-benzoate.—Formulary number, 15: "Caffeine, fifty grammes (50 Gm.) [1 oz. av., 334 grs.]; sodium benzoate, fifty grammes (50 Gm.) [1 oz. av., 334 grs.]; alcohol, a sufficient quantity. Triturate the caffeine with the sodium benzoate and a sufficient quantity of alcohol, to a smooth paste, and dry this by exposure in a moderately warm place. Rub the dry mass to a powder, and keep in well-stoppered bottles. Note.—The product contains 50 per cent of caffeine, and is soluble in 2 parts of water"—(Nat. Form.).
CAFFEINAE SODIO-SALICYLAS (N. F.), Caffeine sodio-salicylate.—Formulary number, 16: "Caffeine, fifty grammes (50 Gm.) [1 oz. av., 334 grs.]; sodium salicylate, fifty grammes (50 Gm.) [1 oz. av., 334 grs.]; alcohol, a sufficient quantity. Triturate the caffeine with the sodium salicylate and a sufficient quantity of alcohol, to a smooth paste, and dry this by exposure in a moderately warm place. Rub the dry mass to powder, and keep it in well-stoppered bottles. Note.—The product contains 50 per cent of caffeine, and is soluble in 2 parts of water "—(Nat. Form.).