Cantharis - Cantharides. - Cantharis vesica-toria. The Beetle, dried ; collected chiefly in Hungary.

Characters.-From eight to ten lines long, furnished with two wing-covers of a shining metallic-green colour, under which are two membranous transparent wings; odour strong and disagreeable. Powder greyish-brown, containing shining green particles.

Substance resembling powdered Cantharis: Kamala, which has no shining particles Composition.-Cantharides contains .20 to .50 per-cent. of cantharidint a greenish volatile oil, and peculiar fatty bodies. Cantharidin, C10H12O4, is obtained as shining colourless prisms, soluble in ether, chloroform, alcohol, and oils, and is the active principle, being a most powerful irritant. Some of the other properties of cantharides may possibly be referable to the oil.

Preparations.

1. Acetum Cantharidis..-1 in 10 of Glacial Acetic, and Acetic Acids.

2. Charta Epigpastica.

3. Emplastrum Cantharidis

Emplastrum Cantharidis. 1 in 3.

4. Emplastrum Calefaciens

Emplastrum Calefaciens. 1 in 24.

5. Liquor Epispasticus

Liquor Epispasticus. Cantharides, 8; Acetic Acid, 4;

Ether, to 20.

6. Tinctura Cantharidis -1 in 80. Dose, 5 to 20 min.

7. Unguentum Cantharidis

Unguentum Cantharidis. 1 in 7.

Action And Uses. 1. Immediate Local Action And Uses

Externally.-Cantharis is a rubefacient and vesicant when applied to the skin, acting upon the nerves and vessels of the part like mustard and other measures of the same class, as described under Sinapis, to which the student is referred. Its effects differ from those of mustard chiefly in being much less rapid, but of a more severe degree. The Emplastrum or Charta has to be applied for a few hours before a sense of smarting, heat, and burning, is felt in the part; small vesicles then form, and at the end of eight to twelve hours have united into a single largo bulla. The removal of the plaster after six hours, and the application of a poultice, will "raise the blister" more effectually and pleasantly. Vesication is decidedly more rapid after the application of the Acetum or Liquor Epispasticus. When the blister has been developed, the fluid is carefully incised, and the raw surface encouraged either to heal by simple dressing, or to discharge by the application of irritant ointments, such as Unguentum Sabinae. Cantharis is the vesicant in ordinary use for purposes of counter-irritation.

Blisters are chiefly employed to control hyperaemia and the inflammatory process; to promote the absorption of morbid products; to relieve pain; and to arrest spasm and other reflex symptoms. The principle upon which they are believed to act is discussed under Counter-irritants in Part III.

Spanish fly is most frequently used in cerebral hyperemia, being applied to the nape ; in acute pleurisy, pericarditis, peritonitis, and meningitis-sometimes in the first stage, especially if pain be severe, but more frequently in the third stage, to promote absorption of effusions and exudations; in subacute or chronic inflammation of the viscera, such as pneumonia, when resolution is slow, or the disease threatens to become chronic; and in subacute or chronic inflammation of peripheral parts, such as the conjunctiva, joints, bones, etc. Neuralgia, if distinctly local in origin and due to congestion or inflammation of the nerves, is sometimes completely relieved by cantharides blisters; and the pains of acute rheumatism are undoubtedly dispelled, by the same means, which is further believed by some physicians to cut short the whole rheumatic process. A blister on the epigastrium is a successful mode of treatment in some forms of gastric pain and vomiting.

In every instance, cantharis should be cautiously applied to children, to persons suffering from kidney disease, and to the aged and infirm. The back must not be blistered in bedridden persons, lest bed-sores be produced. Blisters must never be forgotten or left too long on the skin, otherwise ulceration may be set up, as well as the remote local effects of the drug to be presently described.

Internally.-Cantharis is an irritant to the mouth, throat, and stomach, and must be given well diluted and in small doses of the tincture only.

2. Action In The Blood, And Specific Action And Uses

Cantharidin enters the blood both from the blistered surface and the stomach. The active principle finds its way into all the organs, to which it clings rather tenaciously. In large doses it disturbs the heart, respiration, and nervous system, producing a rapid pulse, headache, sensory disturbances, mental confusion, and finally death by asphyxia. It is not used in this connection.

3. Remote Local Action And Uses

Cantharidin is slowly excreted by the kidneys, and appears in the urine, which conveys it to the bladder and genital organs. Here it sets up a second set of local effects similar to its immediate action. Small doses cause a sense of heat in the perineum, itching of the meatus, frequent desire to micturate, and some diuresis. Larger doses set up acute parenchymatous nephritis, with all its characteristic symptoms, including scanty bloody urine, or even suppression; the penis becomes swollen, and painful erections occur, so that the drug has been described as an aphrodisiac. In women, the uterus may become congested and menstruation may be brought on.

In certain ill-understood cases of kidney disease, cantharis has proved a useful diuretic and renal alterative ; also in some instances of disease or disorder of the bladder, prostate, and urethra, including spermatorrhoea. It is too dangerous a drug to be generally used for this purpose. For the same reason care must be taken to prevent the absorption of cantharidin by the skin.