Discussion.

The average dose of tincture of belladonna leaves is 12 minims. A child 2 years old usually takes 1/7 of an adult dose (Young's rule); 1/7 of 12 minims equals 12/7 or about 1% minims. One drop is about 1/2 minim, so the child receives about 1/3 of the average dose. It should be remembered that size, sex, etc., should also be considered.

(14) What is the approximate percentage of alkaloid in the following prescription:

M.

Discussion.

This prescription contains 25 per cent. of belladonna ointment. Belladonna ointment contains 10 per cent. of the extract (as other vegetable ointments). The extract is about five times as strong as the drug (as most other extracts). The leaves contain 0.3 per cent. of alkaloids, principally atropine. If the ointment of belladonna represents 10 per cent. of the extract, which is five times as strong as the drug, it represents 50 per cent. of the drug, and a preparation containing 25 per cent. of this would represent 12.5 per cent. of the drug (0.50 x 0.25 equals 0.125). The drug containing about 0.3 per cent. of alkaloids, the preparation would contain 0.3 per cent of 12.5 per cent. (0.003 x 0.125 - 0.000375) or 0.0375 per cent. of alkaloids. This, of course, could be calculated directly from the alkaloidal content of the extract, but the student does well to remember the content of the drug, and, for approximate work, the foregoing answers well.

(15) Write a prescription for Fowler's solution, alone, to be taken by drops, so that the patient will get the equivalent of 1/25 grain of arsenic trioxide to each dose.

Discussion.

Fowler's solution (as most other solutions) averages about a drop to the minim. It represents 1 per cent. of arsenic trioxide, therefore 100 drops would represent about 1 grain of the salt, 1 drop about 1/100 of a grain, 4 drops about 4/100 or 1/25 of a grain. It should be remembered that drops vary in size owing to style of dropper, rapidity of dropping and many other conditions.

(16) A patient taking Fowler's solution after meals, gradually increased to 9 drops per dose before showing toxic symptoms. How much, and of what salt, was he getting per day?

Discussion.

In making Fowler's solution 1 per cent. of arsenic trioxide is used. This is acted upon by potassium bicarbonate to form potassium arsenite, which is the form in which arsenic is present in the solution. If the solution represents 1 per cent. of arsenic trioxide, 1 minim would represent Moo of a grain, 9 minims would represent 9/100 of a grain or about Mo grain as a dose. Three doses a day would give a total of nearly 1/3 of a grain.

(17) Write a tonic prescription (for an adult) containing solution of arsenous acid in such amount that there will be an average dose of arsenic trioxide to each teaspoonful of the preparation.

Discussion.

Solution of arsenous acid contains 1 per cent. of arsenic trioxide, or about 1 grain to each 100 minims or 1/100 of a grain to each minim. The dose of arsenic trioxide is1/30 grain, so it would take about 3% minims of the solution to give an average dose of the salt, and each teaspoonful of the prescription must contain that much. A prescription for 4 fluid-ounces would contain about 32 doses, so multiply this (32) by the 3 1/3 minims (for each dose) and the total amount is obtained- 3 1/3 x 32 = 107. In practice we would use 1 1/2 or 2 fluidrachms.

Name, etc.

Date,

M.

Sig

Teaspoonful in water after meals.

(18) The Pharmacopoeia gives 1 1/2 minims as the average dose of Donovan's solution.

(a) How much, and of what, does this dose contain?

(b) How do these amounts compare with the average doses of these salts?

(c) Based on the average doses of its contents, what would be a safe dose of the solution?

Discussion.

(a) Donovan's solution contains 1 per cent. each of arsenous iodide and red mercuric iodide, therefore 100 minims contain about 1 grain each of the salts, 1 minim contains 1/100 of a grain each, 1 1/2 minims contains about 1/66 of a grain of each.

(b) The average dose of arsenous iodide is 1/10 grain, of red mercuric iodide 1/20 grain, so the dose of the solution as stated would be about 3/20 of the average dose of the arsenic salt and 3/10 of the dose of the mercuric salt.

(c) Five minims would contain the average dose of the mercuric salt and 1/2 the average dose of the arsenous salt.

(19) A physician wished to prescribe the tincture of digitalis in drops so that the dose could be easily changed as conditions might require. Write the prescription so that the patient will begin with about 20 minims at a dose.

Discussion.

The tincture of digitalis, as most other tinctures, averages a little more than 2 drops to 1 minim.

Patient's name, etc.

Date,

Big

Begin with forty (40) drops in water as directed.

(Over)

Signature.

On the back of the prescription it is well to specify "Dispense a physiologically standardized, fat-free tincture of digitalis."

(20) Write a prescription for tincture of digitalis so that the patient will get 15 minims in each teaspoonful.

Discussion. •

If the prescription is to contain 15 minims to each fluidrachm (tea-spoonful), it would have to contain eight times as much to each ounce-8 x 15 = 120 minims = 2 fluidrachms. Or, as 15 minims is 1/4 of a tea-spoonful, 1/4 of the prescription must be for tincture of digitalis.

Name of patient, etc.

Date,

M.

Sig

Teaspoonful in water 3 times a day.

(Over)

Signature.

It is well to write on the back of the prescription blank, "Use a physiologically standardized, fat-free tincture of digitalis."

(21) Write a prescription in the metric system calling for 60 capsules, each containing an average dose of a strychnine salt, an arsenic salt and about 2 grains of actual FeCO3.