This section is from the book "A Text-Book Of Materia Medica, Pharmacology And Therapeutics", by George F. Butler. Also available from Amazon: A text-book of materia medica, pharmacology and therapeutics.
Origin. - An alkaloid obtained from nux vomica, and also derived from other plants of the Loganiacece.
Description and Properties. - Colorless, transparent, octahedral or prismatic crystals, or a white, crystalline powder, odorless, and having an intensely bitter taste, perceptible even in highly dilute (1: 700,000) solution. Permanent in the air. Soluble at 15o C. (59o F.) in 6400 parts of water, in no parts of alcohol, in 2500 parts of boiling water, and in 12 parts of boiling alcohol; also soluble in 7 parts of chloroform, but almost insoluble in ether.
Dose. - 1/64-1/16 grain (0.001-0.004 Gm.) [1/64 grain (0.001 Gm.), U. S. P.].
Strychninas Nitras - Strychninae Nitratis - Strychnine Nitrate (U. S. P.). - Colorless, glistening needles, odorless, and having an intensely bitter taste; permanent in the air. Soluble in water (1: 42), alcohol (1: 120), and glycerin (1: 60); much more soluble in warm water or alcohol. The nitrate contains no water of crystallization and is permanent in the air. - Dose, "Average dose: 1/64 grain (0.001 Gm. = I milligramme)," U. S. P.
Strychninas Stilphas - Strychninas Sulphatis - Strychnine Sulphate (U.S. P.). - Description and Properties. - Colorless or white, prismatic crystals, odorless, and having an intensely bitter taste, perceptible even in highly dilute (1: 700,000) solution. Efflorescent in dry air. Soluble at 25o C. in 31 parts of water and in 65 parts of alcohol; also soluble in 2 parts of boiling water and 8.5 parts of boiling alcohol. Almost insoluble in ether. - Dose, 1/64-1/16 grain (0.001-0.004 Gm.) [1/64 grain (0.001 Gm.), U. S. P.].
Strychnine or its salts enter into a number of official preparations.
Antagonists and Incompatibles. - Chloral, chloroform, ether, and other of the methane derivatives antagonize the toxic action of strychnine.
Physiological Action. - Since strychnine fully represents the physiological action of nux vomica, that of the former is here given.
Externally and Locally. - In large doses strychnine acts as an antiseptic, but on account of its poisonous nature it is too dangerous to be serviceable. When applied locally to unicellular organisms, in very dilute solutions, the drug acts as a stimulant, increasing their movements. In slightly more concentrated solutions strychnine arrests these movements and destroys life.
Internally. - Digestive System. - Strychnine is an excellent stomachic tonic, improving the appetite greatly and aiding digestion. By its action as a bitter it reflexly stimulates the saliva and increases the secretion of gastric juice, and by imparting tone to the muscular walls of the intestines it increases peristalsis and allays constipation when due to lack of muscular tone. Strychnine is fully absorbed and exerts its chief activities in the spinal axis.
Circulatory System. - Strychnine stimulates the heart by its action on the cardiac muscle. Pharmacologically the pulse should be decreased, owing to the stimulating action of the vagus center in the medulla. But this depressing influence seems to be overcome by the direct stimulating action upon the heart-muscle. In therapeutic doses it is generally held that the pulse is slightly increased. In poisonous doses the pulse is slowed and weakened, owing to overstimulation of both the heart-muscle and the motor mechanism. There is marked increase in the blood-pressure, with constriction of the vessels, particularly those of the viscera.
Nervous System. - Strychnine increases markedly the excitability of the central nervous axis. On the cerebrum it acts as an excitant, particularly keying up the patient. The motor cortex is somewhat stimulated. The acuity of the special senses is heightened. It stimulates attention. Even its cerebral action may be interpreted, however, as due to an increase in the reflex excitability. Physiologically it may be said that the motor and sensory neurons are more closely bound together, either being more permeable to nervous influences or their insulation-becomes reduced. There is no direct impairment of consciousness as the result of large doses.
Spinal Cord and Peripheral Nerves. - The first symptom of the drug is an increase in the spinal reflexes. This Holton and Muir-head think is due to a diminished resistance between the cells in the anterior and posterior horns of the cord. Normally, stimulation of a certain part - as, for instance, of a frog's toe - simply occasions a movement of the part stimulated, no other point being affected. But under the influence of strychnine the slightest stimulation is often sufficient to throw the whole body into tetanic contraction, showing that not only is the resistance in the normal path followed by lessened reflexes, but that resistance in all directions is diminished to such an extent that the impulse affects the entire muscular system. This action on the reflexes is principally on the cord. In fact, the action of strychnine upon the cord seems to be more powerful than upon any other portion of the central nervous axis. Very large doses of strychnine cause paralysis of the motor apparatus, with loss of voluntary movement, due to overstimulation of the reflex centers in the cord, producing exhaustion.
It must be remembered that strychnine does not increase the automatic powers, but simply augments their susceptibility to external stimulation; the slightest external stimulus leading to a greatly exaggerated reflex; he exact mechanism in man is not yet known. Analogies drawn from the reflexes in frogs are not reliable. The reflexes in the human spinal cord are so complex that a study of the action of strychnine on monkeys alone will probably unravel the actual feature in its activity.
Respiratory System. - By the stimulating effect of strychnine upon the respiratory center in the medulla the breathing is rendered quicker and deeper. Owing to the tetanic contractions of the respiratory muscles, under poisonous doses the breathing is greatly interrupted, and the patient may become asphyxiated. At length, the respiratory muscles becoming completely exhausted, death ensues either from excessive tetanic contraction and asphyxiation or from central respiratory paralysis. It is to be noted that the heart continues to beat for some time after respiration has ceased.