This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol2", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
Lobelia has already been sufficiently treated of, in all its relations, except as an emetic. (See page 135.) it will be necessary to say but a few words of it in this capacity. in its emetic operation, it is prompt and powerful, but is apt to be attended with distressing and continued nausea and relaxation; and, in some instances, it cannot be made to act, in any safe dose, or, indeed, in any quantity whatever. in these latter cases, its use, if persisted in with the object of vomiting, is liable to cause great and dangerous prostration; and death has in numerous instances taken place.
In view of the above facts, it would seem that lobelia is not calculated for ordinary employment as an emetic. Though it may often act well, and answer all the desired purposes, yet we have no right to expose a patient to the chances of danger or great inconvenience, to attain an object which may be accomplished quite as beneficially, and without risk, by other medicines. The only circumstances which would justify the employment of lobelia as an emetic, are the absence of any safer medicine in cases of emergency, and the existence of symptoms which offer a strong indication for those effects by which it is distinguished; much nausea, namely, and great relaxation. Such an indication is presented in the paroxysm of spasmodic asthma, in which lobelia is efficient probably beyond all other medicines, and in the spasm of croup when the disease refuses to yield to the ordinary measures. Even in asthma, as it will frequently afford relief in nauseating doses, it is, I think, better to use it in quantities sufficient merely to produce this effect, without vomiting.
When given as an emetic, the dose should not be repeated indefinitely, if preceding doses fail. As already stated, the most fatal results have followed this kind of reckless or ignorant use of the medicine. Unless the first two or three doses vomit, it should not be carried further; nor even so far, should symptoms of general relaxation exist. Under such circumstances, if vomiting be necessary, recourse should be had to other medicines.
The dose of the powder, as an emetic, is from ten to twenty grains; of the officinal tincture, about half a fluidounce; for an infant one or two years old, one or two grains of the powder, or from twenty to forty minims of the tincture.
Besides the above emetics, there are many other vegetable products which have this property in a greater or less degree, and a few which may be resorted to under peculiar circumstances, or in cases of emergency. The following appear to require a brief notice.