This section is from the book "A Text-Book Of Pharmacology, Therapeutics And Materia Medica", by T. Lauder Brunton. Also available from Amazon: A text-book of pharmacology, therapeutics and materia medica.
The medicinal use of strychnine is said to cause in some cases fits resembling those of tertian ague.1 It is not improbable that these are true ague fits, due to malaria, the action of which has been aided by that of strychnine on the vaso-motor centre (cf, p. 287, and action of opium, p. 862).
Strychnine stimulates the motor ganglia of the heart, for Dr. Cash and I found that when a frog is under the action of strychnine a ligature placed between the sinus venosus and auricle did not stop the auricle and ventricle as in Stannius' experiment (p. 319), and if this experiment has already been performed, strychnine injected into the interior of the ventricle causes the auricle and ventricle to recommence beating.2 The action of strychnine on the motor centre in the heart is probably similar to its action on the vaso-motor and respiratory centres.
Respiration is quickened and rendered more deep, owing to stimulation of the respiratory centre, just as in the case of the vaso-motor centre the spinal part of the respiratory centre is rendered so active; if strychnine be given to an animal and the cord be divided below the medulla, respiration is not entirely arrested, as it usually is; and if strychnine be given to an animal after division of the cord, respiration will recommence (p. 236).
On the Muscles. - These are but little affected directly, but indirectly they become greatly exhausted by the wear and tear due to the convulsions. After death they quickly enter into rigor mortis.
Nervous System. - The sensory nerves are so stimulated that the slightest impression is most distinctly felt; the action of the drug has not been shown to be on the nerves themselves, but probably is due to stimulation of the nerve-centres (pp. 226, 229, and 230). Small doses do not affect the motor nerves, large doses paralyse them. This paralysis is partly due to exhaustion from the convulsions, but not entirely, since if one sciatic nerve of the frog be divided before poisoning, so as to pre1 Lewin, Nebenwirkungen der Arzneimittel, p. 50.
2 Brunton and Cash, St. Bartholomew's Hospital Reports, vol. xvi.
vent any convulsions in the corresponding limb, it still loses its irritability, though not so soon as the undivided nerve.
On the Brain. - Small doses increase the mental powers and sharpen the senses. Large doses cause anxiety and malaise, but the functions of the cerebrum continue until death, the mind remaining clear to the last. The convulsions are not cerebral (pp. 179, 180).
On the Spinal Cord. - The spinal cord is greatly stimulated, so that a slight stimulus through a sensory nerve produces not merely increased reflex action but, by increasing the diffusion or ' radiation ' of impulses, causes general convulsions. This action of strychnine has been supposed to be due to increased excitability of the nerve-cells in the spinal cord, but is more probably caused by an alteration in the comparative rate of transmission of stimuli from one cell to another (pp. 161, 173). The con-vulsant action of strychnine was first localised to the spinal cord by the experiments of Magendie, as already described (p. 180).
Strychnine acts more powerfully when injected into the rectum than when swallowed, contrary to the general rule.
Brucine, thebaine, and some other opium alkaloids act in the same way as strychnine.
The effect of brucine in producing convulsions has been said to depend on admixture with strychnine. Mr. Shenstone prepared some pure brucine, and in experiments with this I have found it cause convulsions and death in rabbits when injected subcutaneously. It appears to be both less powerful than strychnine, and to be eliminated more rapidly, for when given to rats as a paste with butter it caused no symptoms whatever.
Methyl-strychnine and methyl-brucine, like methyl-the-baine, do not affect the cord, but paralyse the ends of the motor nerves, like curare.
Uses. - Strychnine is one of the best gastric tonics in dyspepsia when there is a tendency to catarrh and congestion. It probably acts by perfecting co-ordination between the various functions of the parts concerned in the processes of digestion and assimilation. It probably also increases the movements of the stomach and gives tone to the gastric vessels, and thus relieves congestion of the stomach due to bronchitis, cirrhosis, and cardiac disease (p. 367). As a tonic it is very useful during convalescence from acute diseases, in anaemia, in dyspepsia due to indigestible articles of diet or excess of alcoholic stimulants; also in 'sick headache ' in doses of one minim of tincture of nux vomica in a teaspoonful of water every ten minutes (Ringer).
In doses of 10 min. before meals I have found it prevent frontal headache in persons liable to it.
It also gives contractile power to the intestines and is used as an adjunct to purgative pills. A very good dinner pill is pil. rhei co. gr. iv., pulv. ipecac. 1/2 gr., ext. nucis vom. 1/2 gr.; given before dinner. A few drops of tincture of nux vomica just before dinner both increase the appetite and tend to lessen habitual constipation. In dilated heart it is useful as a cardiac tonic. It is useful as a respiratory stimulant in bronchitis, especially when there is a tendency to failure of respiration.
The night-sweats of phthisis are usually checked by taking 10 min. of tincture of nux vomica at bed-time. The probable mode of action has already been discussed (p. 443). It may also increase the cough during the day.
In depression due to mental overwork it is very valuable, as it increases the mental powers, but we must be cautious not to give it for too long a time. One of the chief dangers of giving it to overworked men is that it increases their powers temporarily and they are tempted to overwork themselves still more.
In some forms of paralysis (hemiplegia, paraplegia, wristdrop), except where there still exist symptoms of irritation, it is serviceable; it is also useful in some forms of local paralysis, as atony of the bladder. It is useful in infantile paralysis after the acute symptoms have passed away.
In sexual debility it is often serviceable. Its marked aphrodisiac action is sometimes inconvenient and interferes with its use as a tonic (p. 450). In some cases where debility is associated with sexual excess, strychnine increases instead of diminishes the weakness, and in such cases bromide of potassium should be employed. It has been used in hysteria and chorea with low spirits. It is a cumulative poison, as it contracts the renal arteries and thus prevents its own excretion (p. 40).