Pharmaceutical Calculations Flashcards

A 250 mg vancomycin dose is prepared in 250 mL of NS and must infuse over 90 minutes. What is the required infusion rate in mL/hr?

Answer: 166.7 mL/hr

250 mL ÷ (90 min ÷ 60 min/hr) = 250 ÷ 1.5 = 166.7 mL/hr.

Calculate the osmolarity of a solution containing 154 mEq/L of sodium and 154 mEq/L of chloride.

Answer: 308 mOsm/L

Total osmolarity = sum of all dissolved particles = 154 + 154 = 308 mOsm/L (equivalent to 0.9% NaCl).

A prescription requires hydrocortisone 2.5% cream, 60 g. How many grams of hydrocortisone active ingredient are needed to prepare this compound?

Answer: 1.5 g

2.5% w/w of 60 g = 0.025 × 60 = 1.5 g of hydrocortisone.

A patient has a GFR of 30 mL/min. A drug is normally dosed at 500 mg every 8 hours for patients with normal renal function (GFR ≥ 90 mL/min). Using proportional dose reduction, what is the renally adjusted dose?

Answer: 167 mg every 8 hours

Adjusted dose = (patient GFR ÷ normal GFR) × normal dose = (30 ÷ 90) × 500 = 167 mg.

How many mL of a 1:1000 epinephrine solution must be drawn up to administer a 0.5 mg dose?

Answer: 0.5 mL

1:1000 = 1 mg/mL; 0.5 mg ÷ 1 mg/mL = 0.5 mL.

A pharmacist needs to prepare 200 mL of a 0.05% benzalkonium chloride solution using a 10% stock solution. How much stock solution is required?

Answer: 1.0 mL

Using C1V1 = C2V2: V1 = (0.05% × 200 mL) ÷ 10% = 1.0 mL of stock solution.

A patient is prescribed digoxin 0.25 mg once daily. The only available tablets are 0.125 mg. How many tablets should be dispensed per dose?

Answer: 2 tablets

0.25 mg ÷ 0.125 mg per tablet = 2 tablets per dose.