Ointments are fatty substances, designed for external use, in which are incorporated certain medicines; their consistence is somewhat like that of good lard, being sufficiently soft to admit of being rubbed into the skin. They are most commonly prepared with benzoinated lard as a vehicle, which should be entirely free from salt or rancidity; soft and hard petrolatum are directed by the British Pharmacopoeia in many instances under the name of hard and soft paraffins; occasionally wax, combined with olive or almond oils, is employed. About one-fifth part of yellow wax is added to the lard in the preparation of many ointments. Glycerite of starch and hydrous wool fat (Adeps Lanae Hydrosus) are also convenient ointment vehicles; they readily mix with water. Sometimes fresh butter is used. Lard may be prepared for this purpose by melting it in twice its quantity of boiling water, stirring the mixture constantly; then setting it aside to cool, and separating the lard when it has solidified. This forms a fair prepared lard (Adeps Suillus Preaeparatus), or the benzoinated lard of the Pharmacopoeia may be used. Substances entering into the formation of ointments, and which are not soluble in the fatty matter, should be reduced to a very fine powder previous to incorporation with it; or, if they are dissolved in alcohol or water as hard extracts, etc., they may be first softened by trituration with a small quantity of one of these solvents. Alcoholic fluids are more difficult to incorporate than concentrated aqueous preparations, and the latter should be employed slightly warmed. When ointments prepared of animal fats are long kept they are very apt to become rancid, hence it is usually preferable to make up only small portions at a time, or whenever required for use. Either benzoic acid, or poplar buds, if not objectionable, or incompatible with the ointment, will, when added to it, prevent in a great degree the disposition to rancidity. About 1 drachm of tincture of benzoin to each pound of lard has been found to answer the purpose much better than benzoic acid in the preservation of this fat from rancidity. This, however, is unnecessary where benzoinated lard has been employed. The greasy odor of ointments may be removed by triturating each ounce of ointment with 10 drops of sweet spirit of niter. According to Dr. C. W. Wright, fats and fixed oils may be preseved free from rancidity and disagreeable odor, for a long time, by melting them with powdered slippery-elm, in the proportion of 1 drachm of the bark to 1 pound of the fat; after 10 to 15 minutes' application of heat, the fat must be strained off. The elm bark communicates an odor to the fat that is scarcely distinguishable from that of the kernel of the hickory nut. Prof. E. S. Wayne long ago recommended paraffin as a substitute for lard; it might be added to lard if some third body could be found which would prevent separation on cooling, or it can be used alone, as is now recommended in the British preparations. In European pharmacy the term unguenta includes both ointments and cerates. Onguent, in French pharmacy, has reference only to ointments containing resinous matter; cerates, to mixtures of fatty bodies and wax; and pommades, to those containing fats only.
Oleic Ointments.—OINTMENTS OF THE OLEATES. M. L'Hermite proposed as a substitute for the oleaginous and glycerinic solution of the alkaloids, solutions of these bases in oleic acid. He objected to the oils from their incapability of dissolving the alkaloids, and to the glycerin from its not possessing unctuous properties. Oleic acid triturated with the alkaloids, dissolves them and their salts perfectly, and may then be perfumed.
- OLEATE OF MORPHINE.—A grain and a half of powdered morphine, 1 ounce of pure oleic acid, and 6 drops of essence of bergamot.
- OLEATE OF QUININE.—A drachm of powdered sulphate of quinine to 10 drachms of aromatized oleic acid; dissolved by the aid of a gentle heat.
- OLEATE OF VERATRINE.—Six grains of powdered veratrine dissolved in an ounce of oleic acid.
- OLEATE OF ATROPINE, or of STRYCHNINE.—Three to 15 grains of atropine, or strychnine, dissolved in 10 drachms of oleic acid.
These oleates will serve for the preparation of ointments, and may be hardened by the addition of stearic acid or a mixture of stearic and palmitic acids, which acids will also dissolve the vegetable bases when heated. Thus: OLEIC OINTMENT OF QUININE.—Take of sulphate of quinine, 1 drachm; oleic acid, 7 ½ drachms; stearic acid (of candles), 2 ½ drachms; fuse and dissolve. OLEIC OINTMENT OF VERATRINE.—Take of veratrine, 6 grains; oleic acid, 6 drachms; stearic acid, 2 drachms; mix and dissolve, etc. Oleic acid is also a good solvent for resinous matters and the volatile oils (Amer. Jour. Pharm., Vol. XXVII, p. 72). (See also Unguentum Zinci Oleati.)