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.
Dr. Gibb was one of the first to ascertain the value of bromides in this disorder, and he found the ammonium salt to act best; it quickly relieved the whoop, i.e., the laryngeal spasm. Dr. G. Harley also early recorded satisfactory cases (Lancet, i. and ii., 1863). I have often verified this use of the bromides, especially in early stages. I order for children 3 to 5 gr. every two to four hours, as a rule not giving more than 20 gr. in the day, because of the depression induced in weakly subjects; I often combine belladonna, and sometimes chloral, with the treatment. Dr. Ringer reports them as useful only in simple, uncomplicated cases, but neither dentition nor a pyrexial state need prevent their use if the spasm continue; they are fairly presumed to lessen congestion in the medulla as well as in the mucous membrane of the fauces, and to diminish reflex excitability.
If catarrh be present, an expectorant may be conjoined, and if bronchitis or pneumonia supervene, the spasm generally subsides for a time, and a different treatment is indicated. The convulsion of pertussis I have frequently seen relieved by bromide, but belladonna is much more serviceable.