This section is from the "A Handbook of Useful Drugs" book, by State Medical Examining and Licensing Boards.
An alkaloid obtained from Atropa belladonna and from other solanaceous plants.
Properties : The alkaloid itself is only slightly soluble in water and is usually prescribed in the form of one of its salts, which are readily soluble.
Incompatibilities: Solutions of atropin are stated to be incompatible with alkalies. While no precipitate of the alkaloid would form, unless the solution were more concentrated than those ordinarily used in medicine, the alkaloid in the presence of alkalies is likely to be decomposed
Solutions of the alkaloid are also incompatible with tannic acid, with Lugol's solution, and with potassiomercuric iodid, which precipitate compounds of the alkaloid, and with salts of mercury, such as the chlorid, which decomposes it.
Action and Uses: Atropin and the related alkaloids act on the sympathetic and especially on the autonomic nervous system. If the ordinary stimulation of these nerves causes motor or secretory activity, the use of atropin will inhibit it, and if the normal action of the nerve is inhibitory, atropin removes the inhibition.
The alkaloid produces a cerebral stimulation which shows itself by quickened thought and speech, eventuating in a peculiar talkative delirium with hallucinations. Larger doses produce unconsciousness and occasional convulsions.
Atropin checks the secretion of saliva so that the mouth and throat become dry. This dryness is due to some extent to a similar effect on the mucous secretions of the mouth, throat and nose. As an application of this action, the drug is occasionally used to check excessive secretion of saliva in ptyalism, mercurial salivation, etc. It is also used in coryza, especially in the first stage, to lessen the congestion and excessive secretion of the nasal mucus. It is held by some to be very useful in sore throat. It is used in case of excessive expectoration in bronchitis, bronchorrhea, etc. It also checks the secretion of saliva and mucus during anesthesia in operations on the throat, larynx, etc.
Atropin lessens the secretion of hydrochloric acid by the stomach. It is given for this purpose in hyperchlorhydria, gastric ulcer, etc. While it has a decided effect on the secretion, its use should not be continued for a long time. It lessens the secretion of the pancreatic juice, or at least prevents the increase that follows the ingestion of physostigmin and other drugs, but does not prevent the action of secretin. It is doubtful whether it has any effect on bile. It is said not to affect the secretion of intestinal mucus. It relaxes spasm of the intestinal musculature and in small doses favors the normal peristalsis. It is therefore of great service in spasmodic affections of the stomach and intestine. It may be prescribed in colic, painful spasms due to gastric, duodenal or intestinal ulcers, spastic constipation, etc. It is a serviceable anodyne in gall-stone colic and may render the use of morphin unnecessary.
In small or moderate doses it acts as a respiratory stimulant, but large doses cause respiratory paralysis. It may be employed with good effect in cases in which the respiration is embarrassed from other than mechanical agents. It is used for this purpose in morphin poisoning, but it should be administered with great care on account of the respiratory depression caused by large doses. To obviate the effect of morphin on the respiration it is given with the latter drug in hypodermic injections. It has also been given with morphin as a preliminary to anesthesia by ether; in such cases it also serves to lessen the salivary and bronchial secretions
By paralyzing the vagus endings atropin increases the rapidity of the heart-beat. Its depressant action on the vagus is made use of in the diagnosis of certain disturbances of the cardiac rhythm, particularly bradycardia. If the slow pulse is due to an organic lesion of the conducting mechanism (heart-block), it will persist in spite of the action of atropin, but if it is due to vagal stimulation, an increased rate usually results from an effective dose.
Atropin in moderate doses relaxes the blood-vessels of the skin so that the skin, especially of the face and upper extremities, becomes red, sometimes showing an eruption closely resembling that of scarlet fever. In larger doses it contracts the vessels of the splanchnic area and raises the blood-pressure. In still larger doses a general fall of blood-pressure occurs, accompanied by a very rapid and feeble pulse. It is not, however, an essential heart tonic.
The secretion of sweat is reduced by atropin. It is used for the suppression of night sweats, especially in pulmonary tuberculosis. A single dose given at night may be followed the next night by a larger dose if the first was not successful. The use of atropin for this purpose should be deferred as long as practicable and discontinued as soon as may be on account of disturbing influence on digestion.
Atropin produces dilatation of the pupil, paralysis of the accommodation and consequent disturbance of vision by a local action on the oculomotor nerve endings in the iris. When the drug is taken internally the effect is due to the atropin circulating in the blood, and is bilateral. When the drug is applied locally the action is unilateral unless some general absorption takes place or some of the solution is introduced into the other eye by accident.
To produce these actions, atropin is employed in solution dropped into the conjunctival sac for the purpose of facilitating the examination of the eye with the ophthalmoscope. The dilatation of the pupil also serves as a diagnostic measure in case of iritis as the pupil dilates irregularly in this disease. The wide dilatation of the pupil also tends to prevent its adhesion to the cornea or lens.
Sufficient absorption may take place from lotions dropped into the conjunctiva to produce general symptoms and even to cause toxic effects.
Atropin is sometimes used externally in the form of ointment of belladonna for the relief of certain forms of neuralgia, especially those in which pain results from local conditions of the nerve or surrounding tissues. It has been advised for local use in the rectum to relieve the pain of hemorrhoids or fissure. It is an old remedy for enuresis, but must be regarded in most cases as a purely empirical treatment to be used after investigation has shown the absence of organic lesions which may be remedied in other ways. It is used for vesical spasm due to irritable neck of the bladder.
While the action of atropin on the milk is not entirely established, it is quite generally used locally in mammitis, galactorrhea and when it is desired to check the secretion of milk.
Dosage: Unpleasant symptoms indicating the beginning of its physiologic effects are produced in some people by 0.0005 gm. or 1/125 grain. It is best, therefore, to begin with half this dose, 0.00025 gm. or 1/250 grain. Doses can be repeated once in two hours until distinct physiologic effects are produced. For the treatment of the stomach the remedy should be given in solution about fifteen minutes before the meal. For action on the bowels it is commonly given at bedtime. The same time is also chosen when giving it for night sweats.
When atropin is being administered the patient or his friends should be warned of the possible appearance of slight toxic symptoms. The first indication is usually dryness of the throat. Some dimness of vision is also likely to be experienced.
Serious poisoning usually begins with rapid pulse, flushing of the skin, talkative delirium, marked dilatation of the pupils, some elevation of the temperature and dryness of the throat and skin. This is followed more or less quickly by unconsciousness, prostration, paralysis of the voluntary muscles and marked vasomotor paralysis.