LESSON VII.

POSOLOGY.

We have to-day to consider the extremely important subject of dosage. It is very necessary for you at the outset to understand that a medicine will exert a very different effect according to the dose administered; thus, tartar emetic in doses of from 1-16th to 1-6th of a grain acts as a diaphoretic; in doses of from 1-6th to a grain, when tolerance is established, it will act as a depressant; and in doses of from 1 to 2 grains it will produce emesis.

There is one matter of great interest and import connected with posology to which sufficient attention is not paid by the generality of practitioners-I allude to the modification of action exercised by a medicinal agent according as it is administered in one large dose or in several small doses at stated intervals. We have yet much to learn concerning this matter, and the subject opens up for you a wide field for original investigation. One of the most pungent writers in one of the most incisive articles which ever issued from his thus expresses himself: "No greater service could be performed by the colleges or the great medical societies than the formation of a committee of competent men for the special investigation of this question of dosage for it is a subject which is as yet only in its infancy, and the best knowledge which exists about it is undoubtedly confined to a very small section of the medical profession."

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I have recently published, for the use of students and practitioners, a Posological Chart, (a) in which I have endeavoured as far as possible to assist the memory and to facilitate reference. I purpose in this lesson to give you such a summary of the contents of this chart as will enable you to obtain and retain such a knowledge of official dosage as will be sufficient for the exigencies of ordinary practice. I use the term "official dosage" advisedly, for exception must be taken to many of the posological dicta of the British Pharmacopoeia. For instance, the Pharmacopoeia directs as a maximum dose of tincture of digitalis 30 minims, whereas, half an ounce is not unfrequently given in delirium tremens. A drachm is the maximum dose recommended for tincture of henbane, but halfan-ounce of that preparation is often given with benefit to maniacal patients. The minimum dose stated for tincture of belladonna is too large, and the maximum dose is too small. On the other hand, the maximum dose recommended for tincture of nux vomica would tetanise many a patient. A drachm is allotted as the maximum dose of succus conii, but I have myself seen an ounce of that preparation administered with great benefit. The Pharmacopoeia specifies 5 grains as the extreme dose of sulphate of quinine, a dose which would be utterly useless in many cases of intermittent fever, &c. Again, the minimum dose recommended for strychnia and the salts of morphia is much too large.

(a) Posological Tables: being a Classification of the Doses of all Officinal Substances? Third Edition. London: Baillière, Tindall, and Cox, King William Street, Strand.

Less than a year ago the late Dr. Anstie directed the attention of the profession to these defects in our "official dosage." (a) You will understand, therefore, that although in apportioning doses I have followed the British Pharmacopoeia as an authority, I dissent in many instances from the recommendations in that volume. The doses which I am about to give are those for adults, so that I will ask your attention to the methods of Gaubius and Young for regulating doses according to age.

"For children under twelve the doses of most medicines must be diminished in the proportion of the age to the age increased by 12." Thus :

(a) Practitioner, vol. ix. p. 259. 1873.

Not only must age be taken into consideration in apportioning a dose, but sex, habit, temperament, idiosyncrasy, disease, race, and climate must all receive due consideration. It is unnecessary for me to do more than remind you that certain drugs, as opium, are very badly borne by children.

In the following posological summary I will adopt the classification which I have used in my chart.

INORGANIC SUBSTANCES.

Dilute acids, average dose m v.-xx., except acid. hydrocyanic. dil., the dose of which is mii.-viii., and acid. acetic. dil., the dose of which is 3.-i.

The dose of acid. sulph. aromat. is the same as that of the dilute acids.

The dose of acid. sulphurosum is mxxx.-3j.

The following are the doses of the solid acids :

Ammonium.-Dose of all the salts is gr. v.—xx., except the carbonate, the dose of which, as a stimulant, is gr. iii.—x., and as an emetic, gr. xxx., well diluted.

Potassium.-The dose of sulphurated potash is gr. iii.-vi.; that of iodide of potassium is gr. ii.-x.; that of the bromide, carbonate, chlorate, and nitrate is gr. v.—xxx.; that of the bicarbonate is gr. x.—xl.; and that of the acetate, citrate, sulphate (purgative), tartrate, and acid tartrate is gr. xv.-3. The dose of either of the two latter salts when they are used as purgatives is Zii-iv.

Sodium.-Arseniate, gr. 1-16th-1-8th; valerianate, gr. i.-v.; hypophosphite, gr. v.-x. ; dried carbonate, gr. iii.-x.; carbonate, gr. v.-xxx. ; acetate, biborate, bicarbonate, and sulphite, gr. x.-3.; effervescing citro-tartrate, 3i.-ii. ; tartarated soda, 3ii.-iv.; and phosphate and sulphate, 3ii.-3.

Lithium.- Carbonate, gr. iii.—vi.; citrate, gr.

V.-X.

SALTS OF ALKALINE EARTHS.

Barium. The dose of the chloride is usually given