Ceratum Cantharidis (U. S. P.)—Cantharides Cerate.
Related entry: Cantharis (U. S. P.)—Cantharides
SYNONYMS: Emplastrum cantharidis, Emplastrum vesicans, Emplastrum epispasticum, Emplastrum vesicatorium, Blistering cerate, Blistering plaster.
Preparation.—"Cantharides, in No. 60 powder, three hundred and twenty grammes (320 Gm.) [11 ozs. av., 126 grs.]; yellow wax, one hundred and eighty grammes (180 Gm.) [6 ozs. av., 153 grs.]; resin, one hundred and eighty grammes (180 Gm.) [6 ozs. av., 153 grs.]; lard, two hundred and twenty grammes (220 Gm.) [7 ozs. av., 333 grs.]; oil of turpentine, one hundred and fifty cubic centimeters (150 Cc.) [5 fl℥, 36♏]; to make one thousand grammes (1000 Gm.) [2 lbs. av., 3 ozs., 120 grs.]. "Moisten the cantharides with the oil of turpentine, and set the mixture aside, well covered, for 48 hours. Then add it to the yellow wax, resin, and lard, previously melted and strained through muslin, and keep the mixture in a liquid condition, by means of a water-bath, stirring occasionally, until its weight has been reduced to one thousand grammes (1000 Gm.) [2 lbs. av., 3 ozs., 120 grs.]. Then remove it from the bath, and stir it occasionally until it is cool"—(U. S. P.).
This preparation contains 32 per cent of cantharides, and will always vesicate, providing the flies used are of good quality. It should not be heated, in preparation, higher than 100° C. (212° F.), lest the catharidin be lost with the aqueous vapors given off from the powder employed, thus reducing the strength of the cerate. The vapors given off, when heating higher than the above-mentioned point, are liable to produce vesication of the hands and face of the operator. Turpentine, being a solvent of cantharidin, is employed to render that body more readily soluble in the fats employed. In 1860, Wm. R. Warner proposed a formula, which differs principally in embodying an alcoholic extract of cantharides, in place of the powdered drug. This formula was adopted by the U. S. P., of 1880, under the name of CERATUM EXTRACTI CANTHARIDIS, and is by many preferred to the present official cerate. This is practically reproduced in the formula of the National Formulary given below.
Action and Medical Uses.—As a blistering agent (see Cantharis).
"CERATUM EXTRACTI CANTHARIDIS (N. F.). (U. S. P., 1880). Cerate of extract of cantharides.—Formulary number, 20: Cantharides, in No. 60 powder, three hundred grammes (300 Gm.) [10 ozs. av., 255 grs.]; resin, one hundred and fifty grammes (150 Gm.) [5 ozs. av., 127 grs.]; yellow wax, three hundred and fifty grammes (350 Gm.) [12 ozs. av., 151 grs.]; lard, three hundred and fifty grammes (350 Gm.) [12 ozs. av., 151 grs.]; alcohol, a sufficient quantity.
"Moisten the cantharides, with one hundred and eighty cubic centimeters (180 Cc.) [6 fl℥, 41♏] of alcohol, and pack firmly in a cylindrical percolator; then gradually pour on alcohol, until one thousand eight hundred cubic centimeters (1800 Cc.) [60 fl℥, 415♏] of percolate are obtained, or until the cantharides are exhausted. Distill off the alcohol my means of a water-bath, transfer the residue to a tared capsule and evaporate it, on a water-bath, until it weighs one hundred and fifty grammes (150 Gm.) [5 ozs. av., 127 grains]. Add to this the resin, wax, and lard, previously melted together, and keep the whole at a temperature of 100° C. (212° F.), for 15 minutes. Lastly, strain the mixture through muslin, and stir it constantly until cool" (Nat. Form).
CAMPHORATED CANTHARIDAL PLASTER.—A camphorated cantharidal plaster is prepared by spreading a strong ethereal (or chloroformic) solution of camphor on a plaster of cantharides cerate. This, on evaporation, leaves a film of camphor on the surface of the cerate.
Vesicating cloth, or blistering taffetas, are occasionally prepared. The Charta Epispastica of the U. S. P. will probably fulfil all the indications for these various preparations.