Aconitine, 8 gr., dissolved in rectified spirit, 1/2 fl. dr., and mixed with prepared lard, 1 oz. For external application only.

Physiological Action. - General Action. - The action of aconite is exerted most markedly on the peripheral ends of sensory nerves, on the heart, and on the respiration.

In frogs it produces steady loss of motion, both voluntary and reflex, with gradually increasing weakness of respiration, and of the heart, which finally stops in diastole, usually about the same time as the respiration.

In man one of the most marked symptoms is the local tingling and numbness produced in the mouth by aconite or aconitine if they come into actual contact with it. This irritation is not limited to the mouth,' but occurs also in the gullet and stomach, where it produces belching, nausea, and vomiting.

If aconite preparations, or aconitine, are taken in capsules so that they do not touch the mouth or tongue, this local tingling and numbness are hardly felt at all.

After absorption, however, the poison is carried by the circulation throughout the body, and then causes a tingling in all parts of the body in the order of their sensitiveness as determined by Weber. The most sensitive parts are affected first, viz. the tongue and lips, the finger-tips, face, perineum, breast, belly, and last the back.

The heart is quickly affected even by very small doses, and a single drop of the tincture (B.P.) given in water twice or thrice at intervals of a quarter of an hour will in many cases greatly reduce the rate of the pulse. This slowness of the pulse is due to an action of the aconite upon the vagus-roots, and does not occur after the administration of atropine. In some cases of disease also the pulse seems little affected by aconite. In larger doses the vaso-motor centre becomes gradually paralysed, while the heart remains slow, the blood-pressure falls greatly, and the pulse is not only slow but exceedingly weak and irregular.

Great muscular weakness and dyspnoea occur, the respirations being slow, shallow, and feeble. The dyspnoea, and probably the weakness also, depend to a considerable extent upon the feebleness of the circulation and consequent imperfect nutrition of the nerve-centres, for the administration of atropine lessens the dyspnoea.

In addition to this, however, there must be a direct paralysing action on the respiratory centre, and death usually occurs from stoppage of the respiration.

When the heart is examined immediately after death, it is generally found to be still pulsating, although sometimes it is found to have stopped and even lost its irritability. In the latter stage of aconite poisoning the effects of imperfect respiration may become manifest in the livid colour and anxious appearance of the face, the cold sweat on the skin, and sometimes protrusion of the eyes with dilatation of the pupil.

Death is sometimes preceded by convulsions, which do not appear to be entirely due to asphyxia.

Action on Individual Organs. - The muscles are little if at all affected by aconite. The terminations of the motor nerves appear to be first irritated, so that fibrillary twitchings of the muscles occur in a frog; afterwards they are paralysed. The peripheral ends of sensory nerves in the skin and mucous membranes are first irritated, so that the peculiar tingling and numbness is felt, and sometimes also intense neuralgia, affecting branches of the fifth nerve; afterwards they are paralysed. The motor centres of the spinal cord, and the respiratory and vasomotor centres in the medulla, appear to be first slightly stimulated, so that clonic convulsions may occur. The reflex power of the cord is diminished, the sensory ganglia being affected before the motor ganglia. The paralysis of the cord is probably to a great extent, however, due to its imperfect nutrition from failure of circulation. The brain remains unaffected, the mental faculties being usually clear up till death. Sometimes drowsiness occurs, which may, however, be due to the circulation; and headache is also observed, which seems to involve the interior of the head, and is distinct from the facial neuralgia observed in earlier stages of the poisoning. Like the motor centres in the cord, the vaso-motor centre in the medulla oblongata appears to be first stimulated and then paralysed, so that the blood-pressure rises at first in rabbits, though it falls in dogs and cats, apparently from the slowing of the pulse produced by stimulation of the vagus-roots (p. 288). Later on, the vaso-motor centre becomes paralysed to a considerable extent, though not entirely, so that the blood-pressure falls greatly. Although not completely paralysed, it becomes insensible to reflex stimulation, so that irritation of a sensory nerve will no longer raise the blood-pressure.

The heart in the frog is first quickened and then slowed. In man or mammals there is first slowness of the pulse, but shortly before death it may become more rapid. This effect appears to depend chiefly upon primary stimulation succeeded by paralysis of the motor ganglia in the heart, the effect in mammals being altered by the simultaneous action of the drug upon the vagus roots in the medulla.

The respiration is at first slow and deep with marked expiratory effort; afterwards slow, shallow, and laboured.

This effect appears to be due to the direct action of the poison on the respiratory centre, together with its indirect action through weakening of the circulation (pp. 238 and 239). Before death convulsions occasionally occur, and these are, to a great extent, due to the indirect effect of the drug through the circulation, but possibly also to a direct irritating effect on a convulsive centre in the medulla.

The temperature falls constantly throughout. The stomach is irritated immediately by the poison taken directly into it, so that violent vomiting may occur; but it may also be irritated by the poison being eliminated by the gastric mucous membrane after injection subcutaneously or into the blood, so that the effects are similar to those produced by the direct introduction of the drug into the stomach (p. 39). The secretion of the salivary glands is increased, and usually the sweat also, possibly other secretions. The intestines are irritated like the stomach, and diarrhoea occurs in consequence.

The pupil at the commencement of poisoning alternately contracts and dilates, the tendency to contraction being most marked; and a similar result occurs from the local application of aconitine to the eye. Later on there is extreme dilatation. This dilatation may be due to reflex irritation from the gastrointestinal mucous membrane (p. 218). Aconite quickly passes from the blood into the tissues, for if the greater part of the blood of a poisoned dog is transfused into the veins of a healthy one within a few minutes after poisoning has begun, it produces no effect.

Therapeutic Uses of Aconite. - Aconitine is applied locally in the form of ointment in cases of severe neuralgia, a small piece about the size of a pea being rubbed into the painful part. If the neuralgia affects the temple, great care must be taken that the ointment does not get into the eye, as rapid absorption occurs from the conjunctiva, and general poisoning may result.

Aconite liniment is frequently employed in muscular rheumatism; in various forms of neuralgia, such as sciatica; and over swollen and painful joints. Admixture with chloroform facilitates the absorption of alkaloids through the skin, so that a mixture of aconite liniment with chloroform liniment may be more efficacious than either the one or the other separately; but the mixture should be employed with care, and not over too large a surface, to prevent any risk of too rapid absorption.

As a local sedative to the stomach it has been employed in full doses to check the vomiting of pregnancy. Its chief use, however, is in the febrile condition depending upon local inflammations, such as tonsillitis, sore-throat, pleurisy, pneumonia, phthisis, peritonitis, pericarditis, acute rheumatism, gout, erysipelas, otitis, gonorrhoea, and in urethral fever. In many of those conditions small doses of aconite slow the pulse, lower the temperature, and give much relief to the patient. In cardiac disease its action is somewhat uncertain. In nervous palpitation it is sometimes useful, and it may give relief in palpitation depending upon hypertrophy, but frequently it is of no use in this condition. In diseases of the nervous system its internal application alone, or combined with its external use, sometimes gives relief in headache, toothache, noises in the ear, neuralgia, especially in the face, in intercostal neuralgia, and neuralgia accompanying herpes zoster. It has been found useful, also, in some cases of amenorrhoea depending on a sudden check to the menstrual flow, and also in severe menorrhagia.

Mode of Application. - Externally it may be applied in the form of ointment or liniment, internally in the form of tincture or extract. The extract is uncertain in its strength, and death has occurred from the two grains laid down as a maximum dose by the British Pharmacopoeia. The tincture should also be administered in very small doses, as it is difficult to counteract its effect when too much has been given. Instead of giving a large dose, therefore, all at once, it is much better to give it in divided doses, such as one drop in a little water, every quarter or half an hour until the pulse has begun to be affected, and then every hour or two afterwards, according to the necessities of the case, so as to maintain the action (Ringer).