Compounding Calculations: Practical Examples

Calculating Ingredient Quantities

When filling a compounding formula, you must calculate the exact amount of each ingredient. If a formula calls for 2% salicylic acid in 60 grams of ointment, you need: 60 g x 0.02 = 1.2 g of salicylic acid, with the remaining 58.8 g as ointment base.

For solutions, if you need 500 mL of a 5% dextrose solution, you need 25 g of dextrose (500 mL x 0.05 = 25 g) dissolved and brought to a final volume of 500 mL with purified water.

Scaling Formulas

Master formulas may need to be scaled up or down. If the master formula makes 100 capsules but you only need 30, multiply each ingredient by 0.3 (30/100). Always compound a small overage (typically 10-20% extra) to account for losses during preparation.

For a 10% overage on 30 capsules, prepare enough for 33 capsules. This ensures you have enough to fill all capsules and perform quality checks.

Practice Compounding Math

Compounding calculations combine multiple math skills. Practice with PTCB flashcards and mini exams focused on calculation problems.