This section is from the book "Materia Medica Pharmacy, Pharmacology And Therapeutics", by W. Hale White. Also available from Amazon: Materia Medica Pharmacy, Pharmacology And Therapeutics..
Lobelia. - The leaves and tops of Lobelia inflata Linne (nat. ord. Lobeliaceae), collected after a portion of the capsules have become inflated. Synonym. - Indian Tobacco.
North America, in the fields and open woods.
Leaves alternate, petiolate, the upper ones sessile, ovate or oblong, about 5 cm. long, irregularly toothed, pubescent, pale green; branches hairy, terminating in long racemes of small, pale blue flowers, having an adherent five-toothed calyx, which is inflated in fruit, a bilabiate corolla, and five united stamens; odor slight, irritating; taste mild, afterwards burning and acrid.
The chief constituents are - (1) Lobeline, an alkaloid, as a yellowish, oily liquid of pungent taste, having an odor resembling that of tobacco. (2) Lobelacrin (probably Lobeline Lobelate). (3) Lobelic Acid.
Incompatibles. - Caustic Alkalies, as they decompose Lobeline.
Dose, 1 to 10 gr.; .06 to .60 gm.
Dose, 1 to 10 m.; .06 to .60 c.c.
2. Tinctura Lobeliae. - Tincture of Lobelia. Lobelia, 200. By percolation with diluted Alcohol to 1000.
Dose, 5 to 30 m.; .30 to 2.00 c.c.
Lobelia has no effect on the skin, but it is stated that poisonous symptoms may occur from absorption of it through the epidermis.
Gastro-intestinal tract. - Moderate or large doses are powerfully irritant, and thus they cause violent vomiting and purging. A peculiarity of the action of lobelia is that these results are accompanied by very intense prostration, as shown by the feeble pulse, cold sweats, pale skin, and great muscular relaxation.
Circulation. - In the frog the heart is at first stimulated, but soon depressed, and it finally stops in diastole. The blood-pressure falls. This is due partly to the action on the heart, and partly to paralysis of the vaso-motor centres.
Respiration. - Small doses slow respiration, large doses strongly depress the respiratory centre, and death takes place from respiratory failure. The muscular coat of the bronchi is said to be relaxed.
Nervous system. - Toxic doses are required to affect the higher cerebral centres, and then coma and convulsions are produced, but it is not clear how far these results are due to asphyxia. The respiratory and vaso-motor centres, and probably the cardiac, are, as already mentioned, depressed. Experiments seem to show that the motor centres of the cord are also depressed. Muscles and nerves are unaffected.
Lobeline is probably excreted by the kidneys and skin, and is said to have diuretic and diaphoretic properties.
Lobelia has been recommended as a purgative, and as an emetic, but it should not be used for these purposes, because of its great liability to produce collapse. It is employed for the relief of the symptom asthma to relax the muscular coat of the bronchial tubes. A drachm; 4. c.c. of the tincture should be given till nausea is experienced, but it should never be pushed beyond that point. It may also be prescribed for bronchitis accompanied by spasmodic dyspnoea. As an external application tincture of lobelia with an equal quantity of glycerin is a most useful remedy for the relief of pain of acute epididymitis.