Acetum Cantharidis.—Vinegar of Cantharides.
Related entry: Cantharis (U. S. P.)—Cantharides
Preparation.—Take bruised cantharides, 2 ounces; glacial acetic acid, 2 fluid ounces, and a sufficient quantity of acetic acid to make 20 fluid ounces. Mix with the glacial acetic acid 13 fluid ounces of acetic acid; add the cantharides and digest for a couple of hours at a temperature of 93.3° C. (200° F.). After the mixture has cooled, transfer it to a percolator, and when the fluid has ceased to pass add to the residue 5 fluid ounces of acetic acid. After completion of the percolation, press the residue, filter the fluid so obtained, and mix it with the percolate. Finally, by the addition of acetic acid bring the product to measure 1 pint (Imp.). This agrees with the British Pharmacopoeia.
Action and Medical Uses.—This preparation is a speedy blistering agent. Applied to the skin lightly it acts as a rubefacient. But if applied in successive layers with a soft brush, vesication results in from one to three hours. It is convenient to apply to uneven surfaces where vesicating plasters are less likely to remain in contact. After application the blister should be dressed with simple ointment applied on cotton-wool, or soft linen. It is a painful application, and has been recommended for vesicating small areas in superficial neuralgias and rheumatic parts.