Atropina

Atropine

Atropine. Is in yellowish-white, silky, prismatic crystals, without smell, but having a bitter and acrid taste. It is soluble in three hundred parts of water at 60° Fahr., in twenty-five parts of ether, and in much less alcohol. It has a strong alkaline reaction, and forms crystallizable salts with acids.

Atropinae Sulphas

Sulphate of atropine. Is a white, crystalline powder, very soluble in water and in alcohol. Dose, gr.1/120 gr.1/60

Atropinae Salicylas, Atropinae Hydrobromas

The salicylate and hydrobromate, especially the former, are preferred to the sulphate by many ophthalmologists.

Antagonists and Incompatibles

Caustic alkalies act on atropine, and ammonia is evolved; they are, therefore, incompatible with the preparations of belladonna. As respects physiological antagonism, pilocarpus and physostigma counterbalance the actions of belladonna in almost the whole range of its influence, and opium—within certain limitations to be hereinafter described—prevents the respiratory failure, the cause of death.

Physiological Actions

Dryness of the mucous membrane of the nose, mouth, throat, and larynx, is produced by the direct application of atropine to these parts, and the same effects in a more positive manner follow the stomach or subcutaneous administration. A peculiar bluish appearance of the lips, as well as dryness, the author has frequently observed. Nausea is occasionally produced by belladonna, but this effect is probably due to cerebral disturbance. Dryness of the mucous membrane of the stomach and intestines is doubtless produced by belladonna, but increased secretion occurs subsequently, for the stools are rendered more liquid, and are also voided more frequently. Increased peristalsis is most probably a result of the action of belladonna on the unstriped muscular fiber of the intestines.

The active principle of belladonna (atropine) is an extremely diffusible substance. What changes it induces in the blood, if any, are not known. It affects the circulation in a remarkable manner. In some subjects a decided slowing of the heart takes place immediately after the administration of a considerable dose (atropine hypodermatically) and in all, most probably, an instantaneous retardation of the pulse-rate, but a very decided rise in the number of pulsations quickly follows. Not only is the number of the heart-beats increased, but their vigor also, and the area over which the pulsations are distributed is enlarged. It has been conclusively shown that the increased action of the heart is due, first, to stimulation of the cardiac ganglia of the sympathetic, and, secondly, to a paralyzing action on the pneumogastric terminal filaments. In other words, the motor power of the heart is increased in activity, and the inhibiting control is lessened.

The stimulation of the vaso-motor centers by belladonna, or atropine, causes a general rise of blood-pressure owing to contraction of the arterioles. This action of atropine rapidly produces a state of over-excitation, and the irritability of the vaso-motor nervous system, at first increased, soon diminishes; the action of the heart becomes weak, the vessels dilate, and the blood-pressure falls below the normal. In large medicinal doses this effect is easily seen, and, in lethal doses in animals, it may be most certainly demonstrated.

As regards the function of respiration, atropine increases the number and depth of the respiratory movements, but the increase is not in the same ratio as is the elevation of the pulse-beat. The more rapid action of the heart, the increased respiratory movements, the contraction of the arterioles, result in an increased supply of blood to the periphery, more rapid nutritive changes, and consequent elevation of temperature. The rise in temperature in man, from a full medicinal dose, is from ½° to 1° Fahr. This increased body-heat is not long maintained; with the fall in the blood-pressure (vaso-motor paresis), there ensues a diminution in temperature.

In persons of a light complexion, more especially in women, a full dose of atropine is frequently followed by a diffused redness of the skin, not unlike the rash of scarlatina, but wanting in the punctated character of this specific eruption. Redness of the fauces, and some difficulty of swallowing, owing to the dryness of the mucous membrane, occur at the same time, rendering the similitude to scarlet fever very striking. The flush of atropine succeeds to a marked but temporary pallor, which is the first effect, and is a symptom of the vasomotor paresis which succeeds to the vaso-motor stimulation. The belladonna rash is sometimes followed by desquamation.

Dilatation of the pupil is a conspicuous effect of atropine. Whether dropped into the eye, introduced into the stomach, or injected under the skin, prompt and decided dilatation of the pupil follows. A much smaller quantity suffices to produce this effect, when applied directly to the eye. Paresis of the muscle of accommodation is caused by atropine, and this agent also lessens the intraocular pressure. It has been conclusively shown that atropine produces these remarkable effects by an action on the peripheral filaments of the nerves of the iris, and not on its muscular fibers; atropine paralyzes the oculo-motor nerve end-organs, and stimulates those of the sympathetic.

The cerebral effects of belladonna are very characteristic. Headache, vertigo, illusions, hallucinations, a busy delirium, sometimes somnolence, are produced by large doses. The vision is usually lost, the pupils are dilated to the utmost, the eyes are brilliant and staring. Muscular weakness, incoordination, and complete motor paralysis occur; but sensation is not destroyed; although occupied with fancies and illusions, the patient may be indifferent to moderate irritation. The delirium which occurs has a peculiar character: it may be gay and laughing, or busy, the patient being incessantly occupied with a single object or idea; or it may be noisy and furious, the patient fighting and striking all who approach. In lethal doses convulsions may occur, or profound stupor may result after a period of delirious excitement.

The voluntary muscles are not affected by belladonna. The muscular paresis which results from the administration of this drug is due to its action on the motor nerves, but the excitability of these nerves is diminished only, and not wholly destroyed. Both the motor-nerve trunks and the end-organs are affected. The sensibility of the sensory nerves is also impaired, but is not diminished to the same extent as is that of the motor nerves.

Although the action of belladonna is so largely paralyzant, it is not exclusively so, and, under certain circumstances, a tetanic action very similar to that caused by strychnine is developed. In frogs, a day or two after the induction of paralysis by the subcutaneous injection of atropine, the tetanic state occurs. When this state is reached, although the frog lies perfectly limp and motionless if undisturbed, an irritation applied to the periphery will at once cause general tetanic rigidity and spasms. The author was the first to show that this condition of the nervous system is attained in frogs an hour or two after the conjoined administration of atropine and physostigma (eserine).

Atropine, by virtue of the greater than normal transmission of blood through the tissues, increases metamorphosis, and the results of this are represented in an increased elimination of the products of waste.

Atropine is eliminated chiefly by the urine, and the urine of an atropinized animal will dilate the pupil of another animal.