This section is from the book "Botanic Drugs Their Materia Medica, Pharmacology and Therapeutics", by Thomas S. Blair. Also available from Amazon: Botanic Drugs, Their Materia Medica, Pharmacology and Therapeutics.
The leaves of Atropa belladonna, official in every pharmacopeia; the root in the United States and five other countries.
The Solanaceae (belladonna, hy-oscyamus, and stramonium) may be considered together pharmacologically. The nomenclature of the alkaloids is involved; but there are really but two, atropine (racemic) or hyoscyamine (laevorotary) and hyoscine or scopolamine (mixed r. and 1.). Atropine (or hyoscyamine) contains a basic nucleus, tropine, united to a radicle of tropic acid. Homatro-pine is a substitution product. The basic nucleus in hyoscine (or scopolamine) is scopoline, and it is combined with a tropic acid radicle. The alkaloids exist in varying proportions in the various plants of the species, and racemisation occurs in the process of extraction, rendering the alkaloidal therapy complex.
Qualitatively the actions of the various alkaloids are somewhat similar and a statement of the action of Atropine will serve, qualitatively considered. The peripheral action is opposed to those phenomena exhibited by pilocarpine, muscarine, and physostig-mine, paralyzing their stimulating effects on involuntary muscle and gland cells. Atropine paralyzes the nerve-endings of the cerebral and sacral autonomic systems and the true sympathetic nerve-endings in the sweat glands. Certain irregularities occur involving the blocking of impulses.
The peripheral action of atropine tends to diminish secretion and to arrest it in large doses; but the quantitative effect varies, bile and milk being somewhat diminished, pancreatic secretion and gastric secretion being somewhat diminished but largely under normal physiologic stimulus, urine and lymph being little if any diminished, but saliva, tears, mucus of the mouth and respiratory passages markedly diminished, and the sweat diminished most of all.
Atropine produces mydriasis and loss of accommodation; it causes a rise in intraocular tension.
In very small doses atropine annuls the inhibitor effect of the vagus on the heart and its motor action on the muscular coats of the bronchioles.
On the nerve-endings of cerebral nerves in most other tracts atropine has little influence; but in large doses it depresses all involuntary muscle (Cushny). There is slight local anesthesia.
In man atropine induces garrulity, confusion of ideas, emotional instability, and finally delirium due to direct excitation rather than to weakened inhibition. Tremor and coma may be produced and temperature be raised.
The respiration is stimulated by therapeutic doses, and fails under large doses, sometimes thus causing death.
Peripheral effect is twice as active with hyos-cyamine (laevorotary) as with atropine (racemic). The narcotic effect is marked in hyoscine over that of atropine (Peebles). Respiration is best stimulated by atropine.
Of this group of plant drugs belladonna is valuable for effects depending on paralysis of nerve-endings, to control night-sweats, etc. Both belladonna and stramonium are effective as antispasmodics - to control spasmodic asthma. Belladonna the better controls intestinal spasm. Atropine and members of its series are used in ocular conditions. Atropine is preferred for respiratory stimulation. Hyoscyamus and its alkaloids are superior in its role, that of central action and hypnosis. See "Hyoscyamus" and "Stramonium."
In small doses belladonna has been used, sometimes with effect, in congestion of the cerebrum, especially in cases marked by delirium. In pharyngitis and laryngitis small doses are often effective. It cooperates well with aconite in these cases.
In the ordinary medicinal doses belladonna acts well in night sweats, in asthma, in whooping cough with copious secretion, in intestinal spasm and to reduce the griping of purgatives, in the spasm of calculus irritation, in enuresis, in mercurial salivation, in bromidrosis, in gastralgia, in heart disease when it is desired to completely empty the ventricles, or in cardiac pain, in some cases of shock, in the early stages of "colds" or coryza, in vesical spasm, in cystitis, in the insomnia of delirium tremens, in neuralgia of the spasmodic type, and in lumbago.
In some severe spasmodic affections atropine is preferable to belladonna, as also in the passage of a calculus, the use before an anesthetic to check the tendency to excessive cardiac inhibition, as an antidote to morphine, pilocarpine, muscarine, and physostigmine poisoning, and when the respiratory center must be quickly stimulated.
Hyoscine, scopolamine, and allied agents will be discussed under "Hyoscyamus" (q. v.).
Externally is anesthetic and used in liniments and the U. S. P. Unguentum Belladonnae (10% of extract) and in plasters. The official Linimentum Belladonnae combines belladonna and camphor. The extract is used in pills, suppositories, etc.
The average dose of the extract of the leaves is 1/4 grain; fl., 1 minim, but ranges from 1-10 minim up; tincture, from 1 to 10 minims. Atropine is given from 1-200 to 1-100 grain; homatropine hydrobromide, 1-64 to 1-32 grain, in some texts; but the U. S. P. IX gives the average dose as 1-120 grain.
To dilate the pupil and paralyze accommodation. For dilation preliminary to retinoscopy homatropine may be used. Atropine is used for breaking down adhesions of the iris to the lens, and relieving reflex ciliary spasm. Never use if there is glaucoma. After examination with atropine, physostigmine may be instilled to relieve the intra-ocular pressure induced. The technic of the ophthalmic uses are important, as harm may be done if one ventures incautiously. Consult works on ophthalmology.
Eumydrin is the nitrate of methylated atropine and is mydriatic and antihidrotic. It is used like atropine, but is claimed to be less toxic, internal doses ranging from 1-60 to 1-24 grain, and as a mydriatic one-tenth stronger than the usual atropine solutions. Euphthalmin is a combination of maudelic acid and a base similar to that contained in beta-eucaine; it is a synthetic analogue of atropine and resembles it in effect, but is used only in ophthalmic work. It is claimed not to increase intra-ocular tension.