Ratio Strength Calculations with Practice Problems and Answers

[bjwojcik]

Hi Students,

You may already know everything about ratio strength calculations, but in case you need a refresher, here it is. The attached PDF has all the information below along with FREE practice problems and answers.

Ratio Strength

Very occasionally, drug strengths are expressed as ratio strengths.

These calculations have similarities to percent strength calculations.

The units are always g and mL. (If you can find an example where they aren't, let me know!)

Solutions may be w/w, w/v, v/v, or v/w.

The conventional format is 1:another number, where the other number is the amount of final product. Examples: 1:100, 1:500, 1:10,000.

A 1:100 w/w preparation is 1 g active ingredient in 100 g of final product.

It is not 1 g of active ingredient mixed with 100 g of inactive ingredient.

A 1:100 w/v solution is 1 g active ingredient in 100 mL solution.

A 1:100 v/v solution is 1 mL of active ingredient in 100 mL solution.

A 1:100 v/w solution is 1 mL of active ingredient in 100 g of product.

Keys to preforming calculations involving ratio strengths.

Determine the type of solution (w/w, w/v,v/v, v/w).

Assign the units of g to w and mL to v.

Convert from the colon format into the fraction format with the units attached.

Example: 1:1000 w/v becomes 1 g/1000 mL.

Proceed with calculations using DA or RP.

Example: How many mg of epinephrine are in 45 mL of a 1:10,000 solution of epinephrine?

This is a w (mg) of epinephrine in v (45 mL) solution.

1:10,000 w/v is 1 g:10,000 mL

1 g:10,000 mL converted to fraction format is 1 g/10,000 mL.

Proceed with calculations using DA.

45 mL (1 g/10,000 mL)(1000 mg)/g=4.5 mg

Important: Many fatalities have resulted from incorrect calculations involving ratio strength, with epinephrine being one of the most common drugs involved. Be very careful when preforming ratio strength calculations. Most drugs labeled with ratio strength will include the strength listed in mg/mL, which is safer to use.

Ratio Strength.pdf