Pharmaceutical Calculations (15th Edition) Edit edition

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In pharmacology, we usually follow SI units of measurement which includes units such as liter, gram, etc. Until these came into being, a system referred to as apothecaries system was used which included units such as grain, pint, pound, gallon etc.

Irrespective of what system is being followed we can easily switch between units and denominations by using simple multiplication and division, provided we know the equivalence of the units.

Step 1: Find the grams of phenobarbital equivalent to 3/4 gr.

We know:

Multiplying equation on both sides by 3/4, we get:

Thus, 3/4 grains of phenobarbital are equivalent to 0.0486 g.

Step 2: Find the milligrams of phenobarbital equivalent to 0.0486 g.

We know:

Multiplying equation on both sides by 0.0486, we get:

Thus, 0.0486 g of phenobarbital are equivalent to 48.6 mg.

Step 3: Find the grams of hyoscyamine sulfate equivalent to 0.3111 mg.

We know:

Multiplying equation on both sides by 0.3111, we get:

Thus, 0.3111 g of hyoscyamine sulfate are equivalent to 0.0003111 mg.

Step 4: Find the grains of hyoscyamine sulfate equivalent to 0.0003111 g.

We know:

Multiplying equation on both sides by 0.0003111, we get:

Thus, 0.000311 g of hyoscyamine sulfate are equivalent to 0.0048 gr.

Converting the decimal form to common fraction form, we get:

Thus, quantity of hyoscyamine sulfate, expressed as a common ratio, is 1/209.

Answer: Quantity of phenobarbital, in milligrams, is and that of hyoscyamine sulfate, as a common ratio, is