This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
For its action in this way opium is indicated in all kinds of disorder throughout the system, which consists in or depends on nervous irritation. When the capacity to feel, and the power to act fail in the centres, there must be a corresponding depression of their dependent functions, and an irritated or over excited state of these functions must be diminished or cease. The particular affections which may thus be relieved or remedied are extremely numerous. They include pain in all its varieties, abnormal special sensations, irregular muscular contraction of all kinds, restlessness, wakefulness, dyspnoea, etc. The most important therapeutic effects, however, may be ranked under the three following heads.
a. For the Relief of Pain, or the Anodyne Effect. Opium probably relieves pain by an active congestion of the cerebral centres, which, according to the law already stated, at length diminishes or suppresses their sensorial function, or, in other words, renders them insensible to irritant impressions sent to them from other parts of the body. It is not the condition of the suffering part itself that is modified by the opiate, but mainly that of the corresponding nervous centre or centres. The same relief would be obtained, by cutting off the nervous communication between the centre and the diseased part where the source of the pain may exist. As the congestion, in the degree necessary to the suspension of the sensibility of the centres, comes on only after the symptoms of excitement have subsided, it follows that the anodyne operation of opium cannot be among its first effects; and the fact is, that it is not until after the lapse of a considerable time that the relief from pain is experienced. Neuralgia, inflammation, and cancer, are among the affections in which opium is given to fulfil the present indication. The occasions for its use on this score are almost innumerable; and, if it were capable of no other application, it would be an invaluable remedy. Something more is often gained by the relief of pain than a mere abatement of the sufferings of the patient. The affection is itself injurious to health, disturbs all the functions, interferes with sleep, and may even, if continued, destroy life. Opium, therefore, must be considered as not only palliative, but frequently also as remedial, even in its relation to pain alone.
In cases of severe injury, as of a compound fracture, lacerated gunshot wound, etc., the relief afforded by opium, and the support which it yields to the nervous system, are often so great as to spare the necessity of amputation, and thus to save a limb, if not life itself, on the battlefield. (J. J. Chisholm, Lancet, July 7, 1866, p. 14).
b. For the Relief of Spasm or Irregular Muscular Contraction. Spasm is of two kinds, that attended with severe pain commonly called cramp, and that which occurs with little pain or none whatever, as in convulsions. The observations in relation to the anodyne operation of opium apply to cramps so far as the relief of pain is concerned. But it does not follow that the spasmodic contraction should be relieved at the same time with the pain. The probability is that the spasm, in all cases in which the involuntary muscles, and often where the voluntary muscles are concerned, depends upon impressions made, not through the cerebral, but the spinal or ganglionic centres; as in spasm of the stomach, bowels, etc., and in tetanus. Now opium, though it acts on the nervous centres of organic life, does so less powerfully than on the cerebral; and it might be expected to relieve the pain more readily than the spasm, and sometimes the former without the latter; and this is really the case. Nevertheless, it has the effect of relaxing the muscular contraction in very many instances, and is among the most efficient remedies in painful spasms. Larger doses, however, are in general required for this condition than either for pain, or for convulsive movements of cerebral origin, as might be anticipated from the less influence of opium over the spinal and ganglionic than the cerebral centres. Thus, spasm of the stomach demands larger doses of opium than gastrodynia; and tetanus often ten times the quantity that would be required to relieve severe rheumatic pain, in the same muscles.
The relaxation of the involuntary muscular contraction produced through the cerebral centres, as in subsultus tendinum, and various convulsive affections, is probably occasioned partly, in the same manner as the relief of pain, by the diminution of the susceptibility of the cerebral centres through which the irritant cause acts, and partly by the diminished power of action in the centres, which prevents them from transmitting to the muscles the influence that induces contraction.
c. For the Production of Sleep. To produce sleep is another most important indication, which opium is capable of fulfilling beyond all other medicines. It may do this in two modes altogether distinct, When wakefulness is caused by some slight nervous disorder, as not unfre-quently happens, small doses of opium, acting in this respect, as a mere nervous stimulant, like assafetida or Hoffmann's anodyne, occasion sleep by simply relieving this disorder. The patient goes to sleep naturally, because he is not kept awake; and the dose of opium, requisite for this effect, would not exercise the slightest soporific influence upon a person in health. This is not, however, the method of producing sleep to which reference is made at present. The soporific action, now under consideration, is the result of a direct influence of the narcotic upon the brain, and is another example of the indirect sedative influence of opium. The sensorial centres are more deeply congested, under the stimulation of the medicine, than is consistent with the performance of their functions, which are for a time nearly or quite suspended. The capacity to feel, to think, and to act, is alike impaired or suspended; though the spinal centres and those of the medulla oblongata still operate. This condition constitutes sleep. It is a higher degree of the same condition in which pain is relieved. The centres are rendered insensible to pain; while still susceptible to impressions from the special senses, the memory, and the intellect. A little further congestion; and these latter susceptibilities cease more or less completely, and sleep, more or less complete, takes place.
The loss of rest is, in many instances, a most serious complication of disease, aggravating, and probably rendering fatal, cases which might, but for it, end in recovery. Whenever it is not attended with high vascular excitement or inflammation of the brain, it may almost always be advantageously treated with opium. The full dose of the medicine is usually required; and, in some cases, this must be greatly increased beyond the ordinary amount. . In febrile and inflammatory diseases, opium is often indicated in reference to this effect; and in delirium tremens, and certain conditions of insanity, in which obstinate wakefulness is one of the most prominent symptoms, it is the remedy chiefly relied on.
(J. For the Suppression of Morbid Discharges. It has been stated that opium has a powerful influence in diminishing the secretions, especially those from the mucous membrane and liver. This property serves as the ground of its employment in various diseases, consisting in, or connected with a morbid increase of these secretions. Hence its use in diarrhoea, cholera morbus, and epidemic cholera. A similar, though less reliable influence on the kidneys, renders it sometimes useful in morbid increase of the urinary secretion. It checks also excessive salivation. By an action, probably of an analogous character, it often proves useful in hemorrhages. The precise principle on which opium produces either of these effects, that is, a diminution of the secretions referred to, or of hemorrhage, is not certainly known. But it may be conjecturally ascribed to the same indirect sedative influence over the capillaries, which is exercised over the heart itself, and, indeed, more or less over the whole system, through the over-excited and congested state of the cerebral centres on which it acts.
The increase of perspiration produced by opium, especially when combined with ipecacuanha or tartar emetic, is among the most useful of its therapeutic effects. But in this relation, the medicine will be treated of among the diaphoretics.
Not unfrequently several of these indications for the use of opium exist conjointly in the same disease, of which frequent examples will be given when we come to treat of its special applications.