Cantharides, or Spanish fly, consists of the dried beetle, Cantharis vesicatoria, Latr. (Order Coleoptera), which is widely distributed over Southern Europe, living gregariously in olive trees, ash trees, etc. The drug is also official in the U.S.P. The beetles are collected before sunrise, while unable to use their wings, by shaking them from the trees on to cloths spread underneath. They are then killed by means of ammonia, vinegar, sulphur dioxide, or by stove heat. The beetles are from 18 to 25 millimetres long and about 6 millimetres broad, smooth, and of a shining green or bronze-green colour. The wing-cases are long and narrow, and conceal, two transparent, brown membranous wings. When fresh the insects have a strong and disagreeable odour, which diminishes by keeping. This drug is not often adulterated, but occasionally the rose beetle (Cetonia aurata, Lind.) is found mixed with cantharides. This, though similar in colour, is easily distinguished by being much broader. Admixture with beetles deprived of their cantharidin may be detected by determining the proportion of this substance and of the fat; the latter should not be less than 10 percent. Two species of blistering beetles, viz., Mylabris sidae, Fab., and M. cichorii, Fab., are regularly imported from China in considerable quantities, and known as Chinese blistering flies. They are readily recognised by their black wing-cases traversed by three broad yellow bands. These two species, which are very similar in appearance, contain more cantharidin than the official, viz., from 0.75 to 1.9 per cent. They are used as a source of cantharidin, but may not be substituted for the European drug in making official galenical preparations. Corresponding preparations are prepared, however, from mylabris, for use in India and the African and Eastern Colonies (see Mylabris). On incineration, cantharides yields about 7 per cent. of ash.
Constituents.—The chief constituent of cantharides is cantharidin, a crystalline lactone, of which good specimens yield from 0.4 to 0.8 per cent. It exists in the beetles chiefly in the free state, but a varying proportion (about 0.03 to 0.40 per cent.) is combined in the form of salts. Cantharides also contains about 12 per cent. of fat.
Action and Uses.—The drug, or its preparations, when applied to the skin, produces redness followed by vesicles, which coalesce to form a blister. Externally, preparations of cantharides are used as rubefacients, counter-irritants, and vesicants (see Emplastrum Cantharidis below). They should not be applied over very large surfaces on account of the risk of absorption, especially when there is renal disease. Internally, cantharides is very irritating to the alimentary canal; after absorption it produces marked vaso-constriction, and during excretion it produces irritation of the kidneys and urinary tract, so that the urine may contain both blood and albumin. Small doses are still given in cystitis, incontinence of urine, gleet and some forms of nephritis and haematuria. It is administered in the form of tincture of cantharides. For external application the powdered beetles are used in Emplastrum Calefaciens, Emplastrum Cantharidis, and Unguentum Cantharidis. The first plaster mentioned is a "warming" plaster, not tending to blister the skin, but only to cause slight redness. Emplastrum Cantharidis will sometimes raise a blister in a few hours. Unguentum Cantharidis will not blister of itself, but will promote discharge from a blister already produced. For application to surfaces where plasters cannot readily be used, Liquor Epispasticus and Collodium Vesicans are of service. The preparations of cantharides are very common ingredients of stimulating hair-washes, the vinegar and tincture being those most frequently used. The former is preferable in acid washes, the tincture for combination with ammonia. All these preparations owe their activity to cantharidin. In cases of poisoning by cantharides, the same treatment should be adopted as in cases of poisoning by cantharidin.
Dose.—5 to 30 milligrams (1/12 to 1/2 grain).
- Acetum Cantharidis, B.P.—VINEGAR OF CANTHARIDES.
- Cantharides, bruised, 10; glacial acetic acid and distilled water, sufficient to produce 100. Extract the cantharides by maceration and subsequent percolation with glacial acetic acid mixed with an equal volume of distilled water. Vinegar of cantharides is used generally, in a dilute form, to stimulate the growth of the hair, but it should not be prescribed in ammoniacal hair washes. As the quantity of cantharidin in this preparation is apt to vary, Acetum Cantharidini has been suggested as an alternative preparation.
- Ceratum Cantharidis, U.S.P.—CANTHARIDES CERATE.
- Cantharides, in No. 60 powder, 32; liquid paraffin, by weight, 13; yellow beeswax, 18; resin, 18; lard, 17.
- Collodium Cantharidatum, U.S.P.—CANTHARIDAL COLLODION.
- Cantharides, in No. 60 powder, 60; flexible collodion, U.S.P., by weight, 85; chloroform, a sufficient quantity. Exhaust the cantharides by percolation with chloroform, evaporate the percolate to 15, by weight, and dissolve the residue in the flexible collodion.
- Collodium Vesicans, B.P.—BLISTERING COLLODION.
- Pyroxylin, 2.5; blistering liquid, 100. Blistering collodion is used as a blistering agent or counter-irritant, where blistering plasters cannot readily be applied, as to the temple or behind the ear. This preparation contains a less constant proportion of cantharidin, to which its action is alone due, than Collodium Cantharidini, which may therefore be prescribed instead with advantage.
- Emplastrum Calefaciens, B.P.—WARMING PLASTER.
- Cantharides, in coarse powder, 4; yellow beeswax, 4; resin, 4; resin plaster, 52; soap plaster, 32; distilled water, boiling, 20. Pour the water over the cantharides and set aside for six hours, then squeeze strongly through calico and reduce the volume to one-third by evaporation on a water-bath; add the other ingredients, melt, and stir together until well mixed. This plaster is a mild counter-irritant; used to remove pain in rheumatic joints, and where a rubefacient. as opposed to a vesicant, action is required.
- Emplastrum Cantharidis, B.P.—CANTHARIDES PLASTER. Syn. Emplastrum Lyttae; Emplastrum Epispasticum; Blistering Plaster.
- Cantharides, in powder, 35; yellow beeswax, 20; lard, 20; resin, 20; soap plaster, 5. Mix the soap plaster with the previously melted resin, add the beeswax and lard, sprinkle the cantharides into the melted mixture, and stir until cold. Cantharides plaster is usually spread on calico adhesive plaster with a half-inch margin, for blistering purposes. Blisters are used principally to relieve deep-seated inflammation and to promote the absorption of effusions. They act (1) Locally, causing congestion of the surrounding parts, (2) Generally, exciting the medulla reflexly, and so causing vaso-constriction, a rise in blood pressure, and stimulation of respiration, (3) Specifically, influencing the metabolism of some internal organ, the nerves to which proceed from the same segment of the cord as that supplying the blistered area of skin.
- Liquor Epispasticus, B.P.—BLISTERING LIQUID.
- Cantharides, in No. 20 powder, 50; acetic ether, sufficient to produce 100. Moisten the drug With 25 of the acetic ether, pack in a percolator, and set aside for twenty-four hours; then slowly percolate with sufficient of the menstruum to produce the required volume. Blistering liquid is painted on the skin as a vesicant to relieve inflammation of deep-seated parts—on the chest for pleurisy, over the pericardium in pericarditis, over the mastoid process in inflammation of the car, over the painful nerve in neuralgia. The area painted is not usually much larger than a shilling-piece; the blister may be pricked with a sterilised needle, and a little soft boric ointment applied. The use of preparations of cantharides should be avoided in children, the aged, and those suffering from renal disease, since absorption of cantharidin may set up or increase kidney irritation.
- Tinctura Cantharidis, B.P.—TINCTURE OF CANTHARIDES.
- Cantharides, in No. 40 powder, 1.25; alcohol, 100. Tincture of cantharides is sometimes given internally in cystitis, gleet, and renal haemorrhage, but it often irritates the urinary tract, causing pain and strangury. It is used principally in hair lotions (1 in 8) as a stimulant to the scalp. Dose.—3 to 10 decimils (0.3 to 1.0 milliliters) (5 to 15 minims); if frequently repeated, 1 to 3 decimils (0.1 to 0.3 milliliters) (2 to 5 minims).
- Tinctura Cantharidis, P.I.—TINCTURE OF CANTHARIDES, P.I.
- Strength 10 per cent. Prepared by percolation with alcohol (70 per cent.).
- Tinctura Cantharidis, U.S.P.—TINCTURE OF CANTHARIDES, U.S.P.
- Cantharides, in No. 60 powder, 10; alcohol (95 per cent.), sufficient to produce 100. Average dose.—3 decimils (0.3 milliliters) (5 minims).
- Unguentum Cantharidis, B.P.—CANTHARIDES OINTMENT.
- Cantharides, bruised, 10; benzoated lard, 100. Digest the cantharides in the previously melted lard, at a temperature of about 49°, for twelve hours; then strain through calico, gently press the residue, and stir until cold. Cantharides ointment is a counter-irritant. It was formerly used to promote discharge from blisters. Diluted with twice its weight of soft paraffin it is employed as a pomade to stimulate the growth of the hair.
The British Pharmaceutical Codex, 1911, was published by direction of the Council of the Pharmaceutical Society of Great Britain.