This section is from the book "Materia Medica Pharmacy, Pharmacology And Therapeutics", by W. Hale White. Also available from Amazon: Materia Medica Pharmacy, Pharmacology And Therapeutics..
Synonyms. - Spanish Flies. Blister Beetles. The Cantharis vesicatoria De Geer (class Insecta; order Coleoplera.)
Southern and Central Europe, mainly on 01eaceae and Caprifoliacae.
About 25 mm. long and 6 mm. broad; flattish cylindrical, with filiform antennae, black in the upper part, and with long wing-cases and ample, membranous, transparent, brownish wings; elsewhere of a shining, coppery-green color. The powder is grayish-brown, and contains green shining particles. Odor strong and disagreeable; taste slight, afterwards acrid.
The chief constituents are - (1) Cantharidin, C10H12O4, 0.4 to I per cent., the active principle, a crystallizable body forming colorless plates, soluble in Alcohol, Ether, Acetic Ether, Glacial Acetic Acid, Chloroform, and oils. It is found especially in the generative apparatus, the eggs, and the blood. (2) A volatile oil giving the odor and said to have the same action as Cantharidin. (3) A green oil, the coloring principle, closely allied to chlorophyll. (4) Various extractives and salts.
Cantharides Cerate is contained in Emplastram Picis Canthari-datum. See Burgundy Pitch, p. 522.
2. Collodium Cantharidatum. - See Pyroxylin, p. 665.
3. Tinctura Cantharidis. - Tincture of Cantharides. Cantharides, 50; by percolation with Alcohol to 1000.
Dose, 1 to 15 m.; .06 to 1.00 c.c.
Cantharides is a powerful irritant; but it is slower in its action than most irritants. If any of its preparations are applied to the skin, no effect is noticed for two or three hours; then a tingling, burning pain is perceived. Soon the part becomes red from vascular dilatation, the drug now producing its rubefacient effect. The next stage is the formation of several vesicles. These soon run together to form one large bleb full of clear serum. Not only is cantharides an irritant and vesicant, but it is a powerful counter-irritant, probably dilating by reflex action the vessels of the deep-seated organs under the point of application.
Cantharidin can be absorbed by the skin in sufficient quantity to produce internal effects.
Cantharides is hardly used internally in medicine, as it is such a powerful irritant.
Gastro-intestinal tract. - It produces severe gastro-intestinal irritation, the patient suffering from abdominal pain, diarrhoea and vomiting. There may be a burning pain in the throat; the motions and vomited matters may contain blood. These symptoms naturally cause much general depression.
Genito-urinary tract. - The active principle is absorbed into the blood, and a few hours after the gastro-intestinal symptoms have set in the patient complains of great pain in the loins and strangury - that is to say, there is an urgent desire to urinate; the effort is very painful from vesical tenesmus, and the quantity of urine passed is very small; it may contain albumin and blood.