Sterile Compounding Certification Pharmacy Math Calculations
NEED TO KNOW STERILE COMPOUNDING MATH BASICS
CONCENTRATION CALCULATION FORMULAS
For solids %w/w = gm/100 gm w = weight
For liquids %v/v = ml/100 ml v = volume
For a mix of solid and liquid %w/v = gm/100 ml
1% Hydrocortisone (HC) cream contains 1g of HC per 100g of cream.
A 1% solution = 1ml of active ingredient per 100ml of the solution.
A 3% w/v solution = 3g of solid per 100 ml of the solution.
1.Compare 2 numbers in relation to each other ¼ = 1:4
2. When added together make a whole - 1:2:2 = total of 5 parts
Two solutions are combined in a 2:1 ratio to make a final solution. How many mLs of each solution is needed to make 100 ml of the final solution?
In this case, you would need to solve this question using #2 above.
1. Total parts = 3 (2+1)
2. mLs needed for the numerator (top number) = 2/3 x 100 ml = 66.67 mLs
3. mLs needed for the denominator = 1/3 x 100 ml = 33.33 mLs
The total from 2 & 3 above should equal 100 mLs.
To change the strength of a preparation, adding a diluent to it is necessary which would result in the final preparation having a lower percent strength. The most common formula used for liquids and solids is:
V1 x S1 = V2 x S2 (V = Volume and S = Strength (may be entered as whole numbers).
Example: How many mLs of a 0.5% stock solution (SS) is required to make 1.5 L of a 0.05% solution using water as a solvent?
As in proportions, 3 variables must be known to solve for the fourth. Leave percent strength as shown. So for this example….
V1 = ? S1 = 0.5% V2 = 1.5L = 1500ml S2 = 0.05%
V1 x S1 = V2 x S2
V1 x 0.5% = 1500ml (1.5 L) x 0.05%
V1 = 1500ml x 0.05
V1 = 150 ml of stock solution (SS) required.
From above, you know the diluent or solvent is water so 1500 (total) – 150 (SS) = 1350 ml of water required.