## PHARMACY CALCULATIONS REVIEW PROBLEMS

### Percentages and Other Measures of Concentration

• 1) What would be the resulting strength of 500 mL of a 25% v/v ethanol solution is diluted to 1.2 L?

• 2) How many milliliters of mineral oil are contained in 1 tablespoonful of a 55% mineral oil microemulsion? Round to 1 decimal place.

• 3) What is the percentage strength % w/v of a 90 mL of an aqueous solution containing 200 mg sodium benzoate? Round to 2 decimal places.

• 4) How many sildenafil 50 mg tablets are required to prepare 25 mL of compounded 0.2% sildenafil otic drops?

• 5) What is the labelled strength of epinephrine hydrochloride in a 50 gram of a topical gel containing 50 mg of epinephrine hydrochloride? Round to 2 decimal places.

• 6) How many grams of niacinamide are required to prepare 90 g of a 4% acne gel? Round to 1 decimal place.

• 7) If 45 mL of a 5% drug suspension is diluted to 60 mL, what is the concentration of the 60 mL suspension? Round to 2 decimal places.

• 8) A vaginal cream contains 0.01% w/w dienestrol. Express this concentration as a ratio strength, with the first figure in the ratio being 1.

• 9) How many milliliters of a stock solution of 1:750 benzalkonium chloride are required to prepare 15 mL of a 0.01 % w/v ophthalmic solution? Round to 1 decimal place.

• 10) A prescription for a testosterone gel includes 1.2 mL of the surfactant polysorbate 80. How many grams does polysorbate 80 contribute to the total weight of the preparation? (The specific gravity of polysorbate 80 = 1.08). Round to 1 decimal place.

### Osmolarity

• 11) Calculate the theoretical osmolarity (mOsm/L) of 23.4 % sodium chloride injection (MW NaCl = 58.5). Round to a whole number.

• 12) Calculate the theoretical osmolarity of an 8.4% sodium bicarbonate (MW = 84) solution. Round to a whole number.

• 13) How many grams of calcium chloride dihydrate (CaCl2-2H2O) would be needed to produce 90 mOsm of CaCl2? (FW for CaCl2-2H2O = 147. Note: Water of hydration becomes part of the solvent water, so is not osmotically active.) Round to 2 decimal places.

• 14) Calculate the theoretical osmolarity of a 15% w/v mannitol (MW = 182) solution? Round to a whole number.

• 15) A prescription calls for the preparation of 30 mL of a 2% tropicamide ophthalmic solution. How many grams of sodium chloride should be included in the formulation to make it isotonic with tears. (The sodium chloride equivalent for tropicamide is 0.11.) Round to 3 decimal places.

• 16) A prescription calls for the preparation of 15 mL of a 0.5% tobramycin ophthalmic solution. How many grams of sodium chloride should be included in the formulation to make it isotonic with tears. (The sodium chloride equivalent for tobramycin is 0.07.) Round to 2 decimal places.

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