PHARMACEUTICAL MATH I PHRA 1209

Most medication problems can be reduced to simple ratio and proportion problems.  Learning to set up ratios and proportions is an extremely valuable problem solving skill in pharmaceutical calculations.

Ratio

A ratio is the relationship between two factors. 

Ratios may be expressed in the form of 1:5 or as a fraction 1 / 5 .  In English, one would say "1 in 5"  or "one fifth" or "one part in five parts".

If there was one blue pill for every five green pills, the ration would be 1:5 ("one to five" or "one in five").

Proportions

A proportion is where two ratios are equal to each other.  When two ratios or fractions in a proportion are equal, there cross product is also equal.  

The cross product is obtained by multiplying the numerator of one ratio by the denominator of the other ration.  The cross products should be equal if the proportion is correct.

Example:

If three of the four values in a proportion are known, the fourth unknown value can be obtained.

Example:

If a valium injection is available in a concentration of 12 mg per 3 ml, how many mgs of valium would be in a 5 ml injection?

Solve for X mg

mg valium in 5 ml = 20 mg