Ratio Solutions
Ratio solutions are usually prepared in strengths as
follows: 1:10, 1:150, 1:1000, 1:25000, etc., using even
numbers to simplify the calculations. When a solution
is made by this method, the first term of the ratio
expresses the part of the solute (the substance
dissolved in a solvent), while the second term
expresses the total amount of the finished product.
Rules for solving ratio-solution problems are as
follows:
W/W (weight/weight) solution: Divide the total
weight (grams) of solution desired by the larger
number of the ratio, and the quotient will be the
number of grams of the solute to be used.
W/V (weight/volume) solution: Divide the total
volume (in milliliters) of solution desired by the larger
number of the ratio, and the quotient will be the
number of grams of the solute needed.
V/V (volume/volume) Solution: Divide the total
volume (in milliliters) of the solution desired by the
larger number of the ratio, and the quotient will be the
number of milliliters of the drug to be used.
Percentage solutions from stock and/or ratio
solutions:
PHARMACEUTICAL PREPARATIONS
LEARNING OBJECTIVE:
Recall the
composition and physical characteristics of
commonly used pharmaceutical prepara-
tions.
While assigned to a pharmacy or naval vessel, you
may be required to make pharmaceutical preparations.
The following sections will acquaint you with the
composition and physical characteristics of some of
these preparations.
Elixirs
Elixirs are aromatic, sweetened hydroalcoholic
solutions containing medicinal substances. The color
of elixirs varies according to the nature of the
ingredients; some are artificially colored.
Suspensions
Suspensions are coarse dispersions comprised of
finely divided insoluble material suspended in a liquid
medium. To keep the insoluble material suspended, a
third agent, called a suspending agent, is required. The
process of mixing or combining the ingredients to form
a suspension is called reconstitution.
Ointments
Ointments are semisolid, fatty, or oily preparations
of medicinal substances. These preparations are of
such a consistency as to be easily applied to the skin
and gradually liquefy or melt at body temperature.
Ointments vary in color according to their ingredients.
The base of an ointment is generally greasy in texture,
6-16
Example: How many grams of KMNO4 are needed
to make 500 g of a 1:2000 solution?
Solution:
500 ÷ 2000
=
0.25 g of drug needed
500 - 0.25
= 499.75 g of solvent needed
500.00 g total solution
Example: How many grams of bichloride of mercury
are needed to prepare 500 ml of a 1:1000 solution?
Solution:
500 ÷ 1000 =
0.50 g of drug needed
Add sufficient solvent to make 500 ml of solution.
Example: From a 1:10 solution of silver nitrate in
water, prepare 60 ml of a 1.5% solution of the same
ingredients.
Solution: A 1:10 (W/V) solution contains 1 g of
solute and enough solvent to total 10 ml of solution
(finished product). Therefore, 1 ml of the solution
would contain 0.1 g of the solute. Since it is re-
quired that 0.9 g of the solute be used to prepare
60 ml of the required strength, use 9 ml of the stock
solution and enough solvent (water) to make the total
volume measure 60 ml.
Example: How many milliliters of HCl are needed to
prepare a 1:250 solution with a total volume of 500
ml?
Solution:
500 ÷ 250 =
2.0 ml of drug needed