Antispasmodics, the means of removing spasm. Spasm or cramp occurs in muscular structures, and is caused by irritation of the nerves. Spasm consists in an irregular and sometimes excessive action of a group of muscles, or a single muscle, or some particular fibres only of a muscle; and various names are applied to spasms of the different muscles or sets of muscles. The conditions giving rise to spasm are various, and affect one or more parts of the nervous circuit, which may be conceived to consist of an afferent or sensitive fibre conveying sensitive impressions to a nervous centre, the latter transforming them into motor impulses, which, passing out by an efferent or motor fibre to a muscle, stimulates it to contraction. When these contractions take place irregularly, or in a degree disproportionate to the stimuli giving rise to them, or when they arise from stimuli which should not normally occasion them, and more especially when they take place unconsciously or involuntarily, they become spasms. They often arise from organic disease of the nervous centres, as in inflammation of the brain or spinal cord, or their membranes, from tumors and haemorrhages, as possibly in chorea or St. Vitus's dance.
A poisoning of the centres by abnormal constituents of the blood, as in Bright's disease, also gives rise to them. The nervous centres, especially the spmal cord and medulla oblongata, and the sensitive nerves, may become too sensitive, as in tetanus or lockjaw, poisoning by strychnia, and epilepsy. Other forms of spasm are due to special local irritations, as colic to improper food, uterine colic to the introduction of fluids into the uterus for therapeutic purposes, asthma to certain states of the atmosphere, cramps of the feet and legs to cold or constrained positions. In treating these various affections, various drugs may be used, which so far deserve the name of antispasmodics. Heat often relieves many spasms, as colic, cramps of the legs and feet, and the general convulsions of children from intestinal irritation, and may be applied in the form of hot baths or hot fomentations. Abnormal excitability of the spinal cord and medulla oblongata is diminished by bromide of potassium, which does excellent service in epilepsy, and sometimes by belladonna. The newly discovered hydrate of chloral has also the same property. Opium relieves the intense pains of uterine or other colic, and relaxes spasmodically contracted intestinal or uterine fibres.
Ether and chloroform, inhaled, not only diminish but nearly destroy the activity of the nervous centres; they control all the voluntary muscles, and are the most powerful antispasmodics which can be used in any form of spasmodic disease. Unfortunately, their effect is often temporary. It is possible that the physostigma (Calabar bean) and woorara (South American arrow poison) may be practically used in some convulsive diseases. In organic diseases of the brain and cord, the disease rather than the symptom deserves attention. The substances to which the name antispasmodics in the narrowest sense is applied are used either in the treatment of colic, of some children's diseases, in many hysterical affections, and some others. They are the " volatile oils," such as mint, lavender, etc, derived chiefly from the tribe of plants called labiatœ; cajeput oil, from the myi-taceœ; dill, anise, fennel, etc., from the umbelliferœ - from which tribe also are derived the foetid gum resins, such as asafœtida, galbanum, ammoniac, etc. These, with valerian, myrrh, and camphor, derived from the vegetable kingdom; musk and castoreum, from the animal kingdom; cyanide of iron and the oxides of bismuth and zinc, from the mineral kingdom, are among the most valuable antispasmodics.
In the treatment of hysteria, moral, tonic, hygienic, and sometimes surgical measures are of far greater importance than antispasmodics, which at the most can only temporarily relieve symptoms. - Spasmodic affections may be complicated with inflammation, and in that case they require most careful and somewhat different treatment. They may also occur in debilitated constitutions, or in persons of full habit; and here again the treatment differs. Thus the medicines classed under the head of antispasmodics are of small importance in comparison with a correct diagnosis and an appropriate mode of treatment in each special form of spasmodic affection.