3. The Regulation Of The Dose

- Almost every article in the Materia Medica operates differently when given in a small and in a large dose. Tartar Emetic, for example, in doses of from 1/12 to 1/6 of a grain, acts as a diaphoretic and expectorant; in doses of from 1/4 to 1/2 of a grain, as a nauseant; and if carried to the extent of two or three grains, it proves powerfully emetic. A very similar series of effects is produced by graduated doses of Ipecacuanha. The neutral salts are aperient in large doses, and diuretic in small ones, Opium is a stimulant in small, and a narcotic in large doses; and the Oil of Turpentine, in doses of fl. drm. j. - fl. drs. ij. acts as an acrid irritant of the kidneys and genito-urinary organs, whilst in doses of fl. oz. j. especially if combined with Castor Oil, it operates freely on the bowels, without producing any renal or vesical irritation. These are but a few examples out of many which might be quoted; but it may be observed generally, that most of the medicinal substances whose operation is mild and beneficial in small doses, may be converted into powerful poisons by being administered in large quantities.

There is a source of error in regulating the doses of fluid medicines, to which, unfortunately, but little attention is paid. I allude to the differences between the minim and the gutta or drop. They are too often considered as identical, both being regarded as the 1/60th part of a drachm. A reference to the following list will show how erroneous any such conclusion must be: -

Table of the number of Drops of different liquids equivalent to a Fluid Drachm, by Mr. Durand, of Philadelphia.*

Drops.

Acid, Acetic, Crystalliz-able ..................................

Acid, Hydrocyanic (Medical) ...................................

Acid, Hydrochloric. .............

Nitric ..........................

Nitric, Dilute (1 to 7) .................................

Acid, Sulphuric ....................

Sulphuric, Dilute (1

to 7) ..................................

Alcohol (Rectified Spirit) Dilute (Proof Spirit) ..............................

138 120

Arsenite of Potassa (Sol. of)

Ether, Sulphuric ..

Oils of Aniseed, Cinna-

Drops.

mon, Cloves, Peppermint, Almonds, Olives.

Tinctures of Assaftida, Opium, Digitalis, and Guaiacum .........................

T. Ferri Sesquichloridi .......

Vinegar, Distilled .................

of Colchicum, Opium, and Squills ..........

Water, Distilled ....................

of Ammonia (Strong)

(Weak)

Wine (Teneriffe) .................

Antimonial ................

of Colchicum .............

of Opium ....................

* Quoted in Dunglison's Medical Dictionary.

The minim, as affording a certain standard of measurement, should always be employed in preference to the drop; the latter, as is shown by the preceding table, being of extremely different dimensions.

The dose of any given medicine, particularly of narcotics and purgatives, should be regulated rather in accordance with the effect it produces in each individual case, than from published or written directions on the subject; not that these are to be disregarded, but they should be looked upon rather as guides to the dose generally required than as applicable to every instance. It is impossible, in many instances, to lay down positive rules as to the quantity of a certain medicine to be exhibited. Take cancer of the uterus, fox example: here Opium is the sheet-anchor as a palliative; and the dose which at first will afford relief and induce sleep, soon fails to produce these effects, and the quantity requires to be increased almost daily, until enormous doses are required to give the same amount of ease and sleep which were originally produced by comparatively small ones. Iodine, in scrofulous cases, is another example. The tolerance of this medicine varies much in certain individuals, without any peculiar idiosyncrasy existing with respect to it; and a dose which will act beneficially in one case, will be productive of great gastric irritation, &c, in another. The same remark applies to Mercury, and many other medicines.

The following is another circumstance, by no means an uncommon one, with several medicines, which requires the notice of the practitioner, in the regulation of the dose. A scrofulous patient, for example, comes under treatment, and Iodine is administered; for a time, the patient improves rapidly, ulcers heal, glandular enlargements diminish in size, the appetite increases, and the constitution gains tone and vigour. Suddenly, however, from no apparent cause, the reparative process ceases, and the patient, perhaps, retrogrades. Under such circumstances, the dose requires either to be greatly decreased, or, what is still better, the medicine should be discontinued for a few days or weeks, when it may be resumed with the original benefit.

4. The character, period, and form of disease, influence the operation of medicines to a very great degree; and the medical man who treats a disease according to its name, without considering the individual circumstances of each case which comes under his treatment, will find his measures either prejudicially violent, or perfectly inoperative. We know that blood-letting, as a general rule, is a remedy for inflammation; but the practitioner who, on the strength of the fact that he has an inflammation to treat, indiscriminately employs this evacuant, without taking into account all the concomitant circumstances, is, to call it by its mildest name, guilty of a great indiscretion. If, for instance, the disease present any typhoid characters; if it occur in a person of a strongly-marked scrofulous diathesis, or in a scorbutic patient; if for several days it has been allowed to progress unchecked, blood-letting, which, under other circumstances, might have been highly beneficial, would most probably prove in the highest degree prejudicial. If this be true in individuals, no less so is it in epidemics. In the inflammatory fevers which visited Great Britain previous to the year 1820, blood-letting appears to have exercised a most beneficial influence; but, observes Dr. Christison,* in the fevers which have prevailed for some years past, the salutary effects of bloodletting have ceased to be presented. It has been repeatedly remarked, he adds, that for the last fifteen years continued fever has been assuming more and more of the typhoid type, over the whole country, but especially in Edinburgh; a corresponding change has taken place in the effects of remedies, and of bloodletting more than any other. It is also worthy of remark, that in the principal epidemics which have prevailed of late years, a remedy which is highly beneficial at one period appears to possess no efficacy at another. From the history of these epidemics, it appears evident that those persons who are attacked by the disease when it is beginning to decline, recover more rapidly, and in greater proportion, than those who were attacked when the disease first made its appearance, or whilst it was most prevalent. It almost appears that the violence of the disease exhausts itself by the virulence of its action; however this may be, it seems certain that many remedies will prove successful at the wane of an epidemic, which have proved utterly incapable of controlling the disease at its outset or its acme. If this be so, and the history of epidemics appears to warrant the correctness of the statement, it is evident that the period of an epidemic exercises a powerful influence on the action of medicines, the point which it is my object here to illustrate. In individual diseases, this influence is often very marked; numerous examples are met with in daily practice; blisters, for example, are most beneficial in acute inflammation after the violence of the symptoms has been subdued by other remedial means. Opium, in the same disease, is especially useful, generally, after depletion. Stimulant diuretics, which are hurtful in Albuminuria whilst acute symptoms are present, may be given with advantage when the disease is assuming a chronic form. Stimulant diaphoretics are inadmissible in acute febrile attacks, but beneficial in the advanced stages; and, lastly, injections into the urethra, which will prove of the highest service in the first and third stages of Gonorrhoea, would cause stricture, orchitis, inflammation of the bladder, &c, if employed in the second stage, or whilst the inflammatory symptoms run high.