Calculations: Basics and Compounding

How many grams of bacitracin and nystatin are required to prepare 150g of a 2:3 topical bacitracin:nystatin ointment?

60g of bacitracin

90g of nystatin

How many grams of NaCl are in 1 liter of normal saline (NS)?

9 grams

How many grams of NaCl are in 500mL of 1/2NS? Round to the nearest hundredth.

2.25 grams

How many grams of dextrose are in 250mL of D5W? Round to the nearest tenth.

12.5 grams

How many milligrams of triamcinolone should be used in preparing the following prescription? Round to the nearest whole number.

PRESCRIPTION:

triamcinolone (w/v) 5%

Glycerin qs 60mL

SIG: two drops in right ear once daily

3,000 mg

A prescription reads as follows: “Prepare a 3% w/w coal tar preparation; qs with petrolatum to 150 grams.” How many grams of petrolatum are required to compound the prescription? Round to the nearest tenth.

145.5 grams of petrolatum

A pharmacist is compounding a vancomycin oral suspension. The master formulation record says to reconstitute a 5g vial of vancomycin powder for injection with 50mL of sterile water, then dilute with sterile water to 200mL. What is the final percentage strength of the compounded product?

2.5%

If 1,250 grams of a mixture contains 80 grams of a drug, what is the percentage strength (w/w) of the mixture? Round to the nearest tenth.

6.4%

A mouth rinse contains 1/12% (w/v) of chlorhexidine gluconate. How many grams of chlorhexidine gluconate should be used to prepare 18 liters of mouth rinse? Round to the nearest whole number.

15 grams

A pharmacist dissolves 6 tablets. Each tablet contains 250mg of metronidazole. The pharmacist will put the drug into a liquid base to prepare 60mL of a topical solution. What is the percentage strength (w/v) of metronidazole in the prescription? Round to the nearest tenth.

2.5%

If 12 grams of lanolin are combined with 2 grams of white wax and 36 grams of petrolatum to make an ointment, what is the percentage strength of lanolin in the ointment?

24%

Express 1.04% as a ratio strength.

1:2,500

Express 1:4,000 as a percentage strength.

0.025%

There are 50mg of drug in 50mL of solution. Express the concentration as a ratio strength.

1:1,000

How many milligrams of iodine should be used in compounding the following prescription?

Iodine: 1:4,000

Hydrophilic ointment qs ad 10g

SIG: apply as directed

25mg

A 10mL mixture contains 0.25mL of active drug. Express the concentration as a percentage strength (v/v) and a ratio strength.

2.5% (v/v)

1:40

What is the concentration, in ratio strength, of a trituration made by combining 150mg of albuterol sulfate and 4.05 grams of lactose?

1:28

Express 0.00022% (w/v) as ppm. Round to the nearest tenth.

2.2 ppm

Express 30 ppm of copper in solution as a percentage.

0.003%

Express 5 ppm of iron in water as a percentage.

0.0005%

A patient’s blood contains 0.085 ppm of selenium. How many micrograms of selenium dose the patient’s blood contain if the blood volume is 6 liters?

510 mcg

A sample of an intravenous solution is found to contain 0.4 ppm of DEHP. How much of the solution, in milliliters, will contain 50mcg of DEHP?

125mL

What is the specific gravity of 150mL of glycerin weighing 165 grams? Round to the nearest tenth.

1.1

What is the weight of 750mL of concentrated acetic acid (SG = 1.2)?

900 grams

How many milliliters of polysorbate 80 (SG = 1.08) are needed to prepare a prescription that includes 48 grams of the surfactant/emulsifier (polysorbate)? Round to the nearest hundredth.

44.44mL

What is the specific gravity of a 30mL of a liquid weighing 23,400 milligrams? Round to the nearest hundredth.

0.78

What is the weight of 0.5L of polyethylene glycol 400 (SG = 1.13)?

565 grams

A pharmacist has an order for parenteral nutrition that includes 550mL of D70%. The pharmacist checks the supplies and finds the closest strength he has available is D50%. How many milliliters of D50% will provide an equivalent energy requirement?

770mL

How many grams of petrolatum (diluent) should be added to 250 grams of a 20% ichthammol ointment to make a 7% ichthammol ointment? Round to the nearest tenth.

464.3g petrolatum

A patient has been receiving 200mL of an enteral mixture that contains 432 mOsm/L. The pharmacist will reduce the contents to 278 mOsm/L. How many milliliters of bacteriostatic water should be added to the bag? Round to the nearest mL.

111mL

If 1 gallon of a 20% (w/v) solution is evaporated to a solution with a 50% (w/v) strength, what will be the new volume (in milliliters)? Round to the nearest 100mL.

1,500 mL

Using 20 grams of a 9% boric acid ointment base, the pharmacist will manufacture a 5% ointment. How much diluent is required?

16 grams

A pharmacist is asked to prepare 80 grams of a 12.5% ichthammol ointment with 16% and 12% ichthammol ointments that she has in stock. How many grams of the 16% and 12% ointment are required?

10g of 16% ichthammol

70g of 12% ichthammol

When the two quantities are mixed together, the pharmacist will have 80g of a 12.5% ichthammol ointment.

A pharmacist is asked to prepare 1 gallon of tincture containing 5.5% iodine. The pharmacy has 3% iodine and 8.5% iodine tincture in stock. How many milliliters of the 3% and 8.5% iodine tincture should be used? (use 1 gallon = 3,785mL)

1,720mL of the 8.5% iodine tincture

2,065mL of the 3% iodine tincture

A hospice pharmacist receives a prescription for 1% morphine sulfate oral solution. She has a 120mL bottle of morphine sulfate labeled 20mg/5mL and a 240mL bottle of morphine sulfate labeled 100mg/5mL. How much of the 100mg/5mL must be mixed with the contents of the 20mg/5mL morphine sulfate bottle to prepare the desired percentage strength for the patient?

72 mL

A pharmacist must prepare 100 grams of a 50% hydrocortisone powder using the 25% and 75% powders that she has in stock. How much of each is required?

50g of 75%

50g of 25%

What is the osmolarity, in mOsm/L, of normal saline (0.9% NaCl)? MW = 58.5 g/mol. Round to the nearest whole number.

308 mOsmol/L

What is the osmolarity, in mOsm/L, of D5W? MW = 198 g/mol. Round to the nearest tenth.

252.5 mOsmol/L

How many milliosmoles of CaCl2 (MW = 111g/mol) are represented in 150mL of a 10% (w/v) calcium chloride solution? Round to the nearest whole number.

405 mOsmol

A solution contains 373mg Na ions per liter. How many milliosmoles are represented in the solution? MW = 23 g/mol. Round to the nearest tenth.

16.2 mOsmol

How many grams of potassium chloride are needed to make 200mL of a solution containing 250mOsmol/L? Round to the nearest hundredth. K (MW = 39g/mol); Cl (MW = 35.5 g/mol)

1.86g

A solution contains 200mg of Ca ions per liter. How many milliosmoles are represented in the solution? MW = 40g/mol

5 mOsmol

Calculate the osmolar concentration, in milliosmoles, represented by 1 liter of a 10% (w/v) solution of anhydrous dextrose (MW = 180g/mol) in water. Round to the nearest decimal place.

555.6 mOsmol

A patient was ordered 1 liter of D5NS with 20 mEq of KCl for dehydration. How many milliosmoles are in 1 liter of this fluid (MW = 198g/mol, Na = 23 g/mol, K = 39 g/mol, Cl = 35.5 g/mol)? Round to the nearest whole number.

600 mOsm/L

Calculate the E value for mannitol (MW = 182 g/mol). Round to the nearest hundredth.

0.18

The E value for ephedrine sulfate is 0.23. How many grams of sodium chloride are needed to compound the following prescription? Round to the nearest 3 decimal places.

Ephedrine sulfate: 0.4g

Sodium chloride qs

Purified water qs 30mL

Make isotonic

SIG: use 2 drops in each nostril as directed

0.178 g

Calculate the E value for potassium iodide, which dissociates into 2 particles (MW = 166 g/mol). Round to two decimal places.

0.35

Physostigmine salicylate (MW = 413 g/mol) is a 2-ion electrolyte, dissociating 80% in a given concentration (ie. use a dissociation factor of 1.8). Calculate its sodium chloride equivalent. Round to two decimal places.

0.14

The pharmacist receives an order for 10mL of tobramycin 1% ophthalmic solution. He has tobramycin 40mg/mL solution. Tobramycin does not dissociate and has a MW of 468 g/mol. Find the E value for tobramycin and determine how many milligrams of NaCl are needed to make the solution isotonic.

E value: 0.07

83mg

How many mols of anhydrous magnesium sulfate (MW = 120.4 g/mol) are present in 250 grams of the substance? Round to the nearest hundredth.

2.08 mols

How many moles are equivalent to 875 milligrams of aluminum acetate (MW = 204 g/mol)? Round to three decimal places.

0.004 mols

How many millimoles of sodium phosphate (MW = 138 g/mol) are present in 90g of the substance? Round to the nearest whole number.

652 mmols

How many moles are equivalent to 45 grams of potassium carbonate (MW = 138 g/mol)? Round to the nearest thousandth.

0.326 mols

How many millimoles of calcium chloride (MW = 147 g/mol) are represented in 147mL of a 10% calcium chloride solution?

100 mmols

How many milligrams of sodium chloride (MW = 58.5 g/mol) represent 0.25 mmol? Do not round the answer.

14.625mg

How many grams of sodium chloride (MW = 58.5 g/mol) should be used to prepare this solution? Do not round the answer.

Methylprednisolone: 0.5g

NaCl solution: 60mL

Each 5 mL should contain 0.6 mmols of NaCl

0.4212g

A 20mL vial is labeled potassium chloride (2mEq/mL). How many grams of potassium chloride (MW = 74.5 g/mol) are present? Round to the nearest hundredth.

2.98g

How many milliequivalents of potassium chloride are present in a 12 mL dose of a 10% potassium chloride (MW = 74.5 g/mol) elixir? Round to 1 decimal place

16.1 mEq

Calculate the milliequivalents of a standard ammonium chloride (MW = 53.5 g/mol) 21.4 mg/mL sterile solution in a 500mL container.

200mEq

How many milliequivalents of MgSO4 (MW = 120.4 g/mol) are represented in 1 gram of anhydrous magnesium sulfate? Round to the nearest tenth.

16.6 mEq

How many milliequivalents of sodium are in a 50mL vial of 8.4% sodium bicarbonate (MW = 84 g/mol)?

50 mEq

A 74 year old male takes lithium carbonate (Li2CO3) 450mg BID, but reports difficulty swallowing the capsules. How many milliliters of lithium citrate syrup provide an equivalent daily dose of lithium? Round to the nearest whole number. MW of lithium carbonate = 74g/mol

15mL