This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
The action of bromides on the nervous system, especially of the lower animals, has been carefully studied by many observers, but with different and somewhat confusing results. Thus, while Damourette, Pelvet, and R. Amory conclude that the functions of nerve-tissue become paralyzed by its direct local application (Bulletin Th'era-peutique, tome lxxiii., and "Essay on Bromide," 1872), Saison finds no trace of such paralysis (Du Bromure: These, 1868); and while Laborde and Purser are satisfied that reflex function is early abolished (Archives de Physiol., tome i., and Dublin Journal, 1869), Bill holds this to be un-proven, and argues that results with frogs are but little guide to effects on men (American Journal, July, 18G8).
I believe myself, that in this instance there is much analogy in the action of the drug on men and animals, and a careful consideration of the evidence before us warrants the following statements.
In batrachians, the bromides, when injected under, or absorbed through the skin, after producing spasm, exert a local paralyzing effect on the neighboring tissues, whether nervous or muscular. If the injection be made close to the brain or to the cord, the centre which is nearest will be paralyzed soonest; but if absorption occur at a distance, e.g., through the web of foot, then reflex power is first lost, so that pinching or irritation does not excite the usual contractions. The periphery of sensory nerves loses its sensibility very soon afterward; then the motor tract of the cord and motor nerves are affected, and lastly the cerebrum. Most of the characteristic effects of the drug may be seen on frogs after the medulla is divided from the brain, but, if it be left undivided, the persistence of some voluntary power, after the cessation of reflex function, is made evident by movements even after apparent death.
In warm-blooded animals the demonstration of early loss of reflex power is not so complete, but there is evident impairment of sensibility and of cerebral action, with partial paralysis, especially of the hind limbs.
In man, the earliest effects of full doses on the nervous system are usually seen in impaired sensibility, especially of mucous surfaces, such as the fauces and pharynx, the conjunctiva, and the urethral membrane. It is possibly most marked in these regions because the drug is largely eliminated there, but loss of tactile sensibility is also sometimes observed in the palms and the soles. Affection of the nerve-centres is shown, sooner or later, by languor, lassitude, and drowsiness; giddiness is complained of, and exceptionally there may be cerebral excitement; mental working power is temporarily impaired, so that ordinary accounts become puzzling and memory fails. The amount of the drug that produces such symptoms varies in different persons. Dr. Lockhart Clarke has noted them from half-drachm and drachm doses, but usually they are not seen until after much larger quantities have been absorbed. The impaired nerve-condition is known as "bromism," and when developed in an extreme degree, the special senses, sight and hearing, are greatly dulled, reflex and motor power are almost wholly lost, and the cerebral state is one of absolute apathy and indifference bordering upon idiocy. As a rule, these serious symptoms subside quickly on omission of the drug.
In seeking for an explanation of the mode of action of bromide, it is clear that we must go farther than the contraction of minute vessels in the nerve-tissue; we may grant that it produces, in certain doses, such a contraction, and may therefore believe that it irritates or stimulates vasomotor nerves, but, besides this, must be admitted, for toxic doses at least, a direct sedative depressing action on the cerebro-spinal system, both central and peripheral, and, in some instances, the action on the vasomotors is also paralyzing, and is accompanied by relaxation of capillaries and local congestions. It is thus that we may explain the exceptional occurrence of diarrhoea or diuresis under bromides, and more particularly the retinal congestions found by Dr. Nicol after doses of 1/2 to 1 dr. (Medico-Chirurgical Transactions, ii., 1872); but this point requires further investigation.
Nothnagel says the temperature always goes down after large doses in men and animals - after 10 grammes (2 1/2 dr.) by 0.5° to 0.8° C., after 15 grammes by 1.2°C. (Krosz).