Botanical name: 

The dried beetles, Cantharis vesicatoria (Linné), De Geer. (Ord. Coleoptera.) Southern Europe. Dose, 1 grain.
Common Name: Spanish Fly; Synonym: Cantharides.

Principal Constituents.—Crystallizable Cantharidin (C10H12O4) and a volatile oil are said to be the active or vesicating principles.
Preparations—1. Specific Medicine Cantharis. Dose, 1 to 10 drops.
2. Ceratum Cantharidis. Cantharides Cerate. (Blistering Cerate.) Epispastic.
3. Collodium Cantharidatum. Cantharidal Collodion, (Blistering Collodion, Vesicating Collodion). Epispastic.
Specific Indications.—Vesical irritation; paresis of the vesical sphincter; dribbling and involuntary expulsion of urine; teasing desire to urinate, accompanied with tenesmus.

Action and Toxicology.—Applied to the skin cantharis first reddens then slowly blisters. Its final action may be so intense as to cause sloughing and gangrene; or by absorption to cause strangury and acute nephritis. Small doses stimulate the excretion of urine; large doses are destructively irritant. The earliest symptom from moderate doses is irritation of the urino-genital tract, with strangury and burning pain. If continued, or the dose is large, blood and albumen appear in the urine. Large doses produce all the intense agonies of a violently destructive gastro-enteritis and acute inflammation of the kidneys and bladder; with final suppression of urine and death from uremia. Intense burning pain, soreness and tenderness of the abdomen, excessive burning thirst, profuse ptyalism, with cadaverous odor of the breath, rapid breathing, small thready pulse, griping and purging, profuse urination followed by suppression, exceedingly painful micturition drop by drop, priapism, violent sexual desire, and seminal emissions are among the awful results of a toxic dose of cantharis. Six (6) grains of powdered cantharides is the smallest amount known to have produced death. Cases of poisoning are almost always confined to those who take cantharis to produce abortion.

There is no known chemical or physiologic antidote to cantharis. Poisoning by it must be treated on general principles, with opiates to control pain. When non-toxic doses have produced strangury it may be relieved by opium and camphor, and large draughts of water.

Therapy.—External. As a vesicant cantharis acts kindly as compared with some other agents. It is sometimes used as a derivative in deep-seated inflammation, to absorb inflammatory products, and to relieve local pain, as in intractable neuralgias and persistent headache. In Eclectic therapy the use of blisters is scarcely ever deemed advisable, or even necessary.. Certainly they should not be used in states of great debility following grave illness, or the exanthems, nor when renal congestion or inflammation is present. Cantharis has been used in lotions to promote the growth of hair. Howe advised it with bay rum, specific medicine uvedalia, and Fowler's solution, for this purpose. Others have used the cantharidal collodion, painted upon the scalp about every two weeks, to encourage the growth of hair in alopecia circumscripta, with asserted success.

Internal. Cantharis has a limited use in modern specific therapeutics. In very small doses it is a decided stimulating diuretic and special sedative to the bladder. One must be very careful, however, to avoid irritant doses. It is the remedy for vesical irritation, to allay teasing desire to urinate and the tenesmus accompanying it. It is one of the most certain remedies for the day-time enuresis of women, particularly the middle-aged, when due to a paretic condition of the sphincter vesicae; and in women and children with irritable bladders or weak sphincters, in whom coughing, sneezing, or exertion cause an involuntary expulsion of urine. It is equally effective in men who pass their urine with difficulty or dribbling, and intense scalding heat. In minute doses it may be cautiously used in the late stages of acute desquamative nephritis, where the kidneys are weak and functionate sluggishly, every little exertion seeming to produce an increase of albumen in the urine. It has also been advised for the torpid kidney action in the chronic parenchymatous nephritis of inebriates, in pyelitis, and in chronic cystitis. Used carefully in renal medication it may accomplish great good; but when recklessly employed it is a dangerous medicine, producing or aggravating the very conditions sought to be relieved by it.

Cantharis promotes menstruation in atonic amenorrhoea with marked depression. It also increases the sexual appetite and has been used to strengthen the procreative functions. Old gleet and prostatorrhoea are first awakened and aggravated and then relieved by it. Its internal use has been advised in some chronic skin diseases, such as psoriasis, prurigo, lichen, and eczema; upon what grounds we are not advised.

The Eclectic Materia Medica, Pharmacology and Therapeutics, 1922, was written by Harvey Wickes Felter, M.D.