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Pharmaceutical Calculations Flashcards

7 cards from real PSI practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. A drug has a half-life of 6 hours. What fraction of the original dose remains in the body after 24 hours?

    Answer: 1/16

    24 hours equals 4 half-lives; (1/2)^4 = 1/16 of the original dose remains.

  2. A patient has a creatinine clearance of 30 mL/min (normal = 100 mL/min). A renally cleared drug is normally dosed every 8 hours. What is the appropriate adjusted dosing interval?

    Answer: Approximately every 27 hours

    Adjusted interval = normal interval × (normal CrCl ÷ patient CrCl) = 8 × (100/30) ≈ 27 hours.

  3. An aminoglycoside is to be dosed to achieve a peak concentration of 8 mg/L. The patient weighs 60 kg and the volume of distribution is 0.25 L/kg. What loading dose is required?

    Answer: 120 mg

    Loading dose = target Cp × Vd = 8 mg/L × (0.25 L/kg × 60 kg) = 8 × 15 = 120 mg.

  4. A 500 mL bag of 5% dextrose for infusion contains how many grams of dextrose?

    Answer: 25 g

    5% w/v = 5 g per 100 mL; 500 mL contains 5 × 5 = 25 g of dextrose.

  5. A topical preparation contains a drug at 0.1% w/v. How many milligrams of drug are present in 20 mL of the preparation?

    Answer: 20 mg

    0.1% w/v = 0.1 g/100 mL = 1 mg/mL; 1 mg/mL × 20 mL = 20 mg.

  6. A pharmacist mixes 300 mL of a 6% solution with 200 mL of a 1% solution of the same drug. What is the final percentage concentration?

    Answer: 4.0%

    (300 × 6 + 200 × 1) ÷ 500 = 2000 ÷ 500 = 4.0%.

  7. Insulin is available as 100 units/mL in 10 mL vials. A patient requires 30 units twice daily for 28 days. How many vials must be dispensed?

    Answer: 2 vials

    Total units = 30 × 2 × 28 = 1,680 units; each vial holds 1,000 units; therefore 2 vials are required.