This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol2", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
From the above facts, it may be inferred that the acid operates directly on the cerebral and spinal centres, and indirectly upon the lungs and heart, probably first suspending respiration through the want of the proper nervous influence to the pulmonary function, and secondly arresting the heart's action through the want of blood from the lungs. Death, therefore, takes place from asphyxia. Hence the general venous congestion observed after death, affecting the brain, lungs, abdominal viscera, etc. The insensibility, however, is the antecedent of the asphyxia, and depends not upon the want of blood in the brain, but upon the immediate paralyzing influence of the poison.
The convulsions serve in no degree to prove an irritant action of the acid; for the same effect is sometimes produced by a very copious loss of blood.
It would seem also that hydrocyanic acid has a direct sedative effect on the nervous peripheries; for numbness and relief of pain have occasionally resulted from its local action, without any apparent influence on the brain.
In inflammations, it is of little use during the stage of highest action; but sometimes, when the heart remains unusually irritable, after the local excitement has in great measure yielded or been subdued, it may be employed with advantage to calm the circulation. in the pulmonary inflammations, it also acts beneficially by quieting the cough, for which purpose it may be substituted for opium, when the latter medicine is contraindicated by its property of checking bronchial secretion. it is most conveniently used, in connection with expectorants and demulcents, in the form of cough mixtures.
In various nervous diseases it has been extensively used. At one time it had great reputation in pertussis, and was even thought to be adequate to the cure of that affection; but experience has shown that it is useful only as a palliative; and, even in this respect, it has no advantage over the cerebral and nervous stimulants, as belladonna and assafetida. it has also been employed in the paroxysm of spasmodic asthma; but it is quite unequal to the violence of this complaint, unless employed in doses which might prove hazardous; and the disease is, therefore, left to safer medicines. indeed, this is the great disadvantage of hydrocyanic acid, that it cannot be given so as to produce a vigorous therapeutic impression, without the danger of inducing its poisonous effects; a disadvantage which it shares with all the most powerful cerebral and nervous sedatives, but which, in consequence of the great rapidity and violence of its action, belongs to it in greater degree probably than to any other. We are, therefore, compelled to satisfy ourselves with those milder curative influences which can be obtained from small and safe doses. Nervous cough sometimes yields very happily to the medicine. it has recently been employed by Dr. Kenneth McLeod, with great advantage, in various forms of insanity, with especial reference to its efficacy in allaying the paroxysms of excitement so often attendant on that disease. The relief afforded is various in degree and duration; being sometimes complete, in other cases partial; in some temporary, and in others again permanent. He uses it both by the mouth and by subcutaneous injection, and in the ordinary doses, never exceeding six drops. A single dose will sometimes be sufficient; but if no benefit is experienced, or the effect has been dissipated, it may be repeated at the end of an hour. (Med. Times and Gaz., March, 1863, p. 262.)
But it is in diseases of the heart that hydrocyanic acid exhibits, I think, its most valuable powers. in the more violent inflammatory affections of the organ or its membranes, or in the excessive excitement of high febrile disease, it will do little good in safe or prudent doses; nor is it adequate, in such doses, to the control of strong hypertrophic action; but in palpitation and other irregularities in the function of the organ, of no very energetic character, whether purely nervous, or associated with organic disease, I know no medicine better calculated to alleviate the disturbed function, and afford ease and comfort to the patient. I use the officinal diluted acid habitually in such cases, in the dose of two or three drops every two or three hours, in emulsion of sweet or bitter almonds, and often find it to afford relief, after failing with the more powerful action of digitalis. it may be used also in aneurism of the aorta; but, as the indication here is rather simply to reduce the circulation than to regulate it, more good may be expected from digitalis, or the arterial sedatives. it is the element of nervous disturbance in the heart's derangements, that hydrocyanic acid is peculiarly calculated to control.
Some years since, much was expected from hydrocyanic acid in phthisis; and the remedy was often used without due regard to its poisonous powers. While in the height of its vogue in Philadelphia, I happened to hear of two cases of this disease, in which it was supposed to be the immediate cause of death. Such accidents deterred from its continued use, and it has fallen into neglect in the treatment of this disease, at least in its ordinary medicinal form; though, as it exists in wild cherry bark tea, it is still much and advantageously employed in this country. its influence in quieting cough, and in calming the excessive frequency of pulse so common in phthisis, renders it useful as a palliative, and adjuvant of other measures; and its association with a tonic principle, in the bark just alluded to, gives peculiar efficiency to that medicine. Next to cod-liver oil, there is no one medicine upon which I am disposed to place more reliance, in the treatment of phthisis, than upon the wild cherry bark, or Prunus Virginian a of our national Pharmacopoeia.
Gastric Pains. in the neuralgic pains of the stomach so frequent in dyspepsia, whether in the form of gastrodynia, gastric spasm, or pyrosis, hydrocyanic acid is much esteemed by many British practitioners. it is said sometimes to act with great promptness and efficiency in the relief of those pains, when purely nervous; and it has been recommended also in similar affections of the bowels. it has been employed, moreover, in ordinary cholera morbus, and in epidemic cholera; but, in the latter at least of these affections, it can be of little service in any safe dose.
Externally it has been found useful in allaying the itching and irritation of certain cutaneous eruptions, such as lichen, prurigo, eczema, impetigo, etc. The mode of its application will be mentioned, under the several preparations or forms in which the medicine is used.