# Pharmacy Calculation Questions and Answers (Part-3)

#### Q1. An over-the-counter cough remedy contains 120 mg of dextromethorphan in a 60-mL bottle of product. The label states the dose as 1 1⁄2 teaspoonfuls for a child 6 years of age. How many milligrams of dextromethorphan are contained in the child’s dose?

1 1⁄2 teaspoonfuls = 7.5 mL

60 mL/120 mg = 7.5 ml/X mg

X = 15 mg.

#### Q2. The usual initial dose of chlorambucil is 100 mcg/kg of body weight. How many milligrams should be administered to a person weighing 154 lb.?

100 mcg = 0.10 mg

1 kg = 2.2 lb.

2.2 lb/154 lb = 0.10 mg/X mg ; X = 7 mg.

#### Q3. If the dose of a drug is 5 mg/m2, what would be the dose for a patient with a BSA of 1.9 m2?

Answer: 5 mg /1.9 = 9.5 mg.

#### Q4. A physician prescribed 100 units of insulin to be added to 500 mL of D5W in treating a patient with severe diabetic acidosis. How many milliliters of insulin injection concentrate, U-500, should be used?

U-500 insulin contains 500 units/mL

500 (units)/100 (units) = 1 (mL)/X (mL)

X = 0.2 mL

#### Q5. If neomycin sulfate has a potency of 600 g of neomycin per milligram, how many milligrams of neomycin sulfate would be equivalent in potency to 1 mg of neomycin?

600 (g of neomycin)/1,000 (g of neomycin) = 1 (mg of neomycin sulfate)/X (mg of neomycin sulfate)

X = 1.67 mg

#### Q6. A biologic contains 50 Lf Units of diphtheria toxoid in each 2.5 mL of product. If a pediatric patient is to receive 10 Lf Units, how many milliliters of product should be administered?

50 (Lf Units)/10 (Lf Units) = 2.5 (mL)/X (mL)

X = 0.5 mL

#### Q7. Determine the creatinine clearance rate for an 80-year-old male patient weighing 70 kg and having a serum creatinine of 2 mg/dL. Use both the Jelliffe and Cockcroft-Gault equations.

By the Jelliffe equation:

CrCl = [98 - 0.8 × (80 - 20)]/2 (mg/dL)

= 98 - (0.8 × 60)/2 (mg/dL)

= 98 - 48/2 (mg/dL)

= 50/2 (mg/dL)

= 25 mL/min.

By the Cockcroft-Gault equation:

CrCl = [(140 - 80) × 70]/(72 × 2) (mg/dL)

= 60 × 70/144

= 4200/144

= 29.2 mL/min

#### Q8. If a patient is determined to have a serum cholesterol level of 200 mg/dL, what is the equivalent value expressed in terms of millimoles (mmol) per liter?

Molecular Weight (m.w. of cholesterol) = 387

1 mmol cholesterol = 387 mg

200 mg/dL = 2000 mg/L

387 (mg)/2000 (mg) = 1 (millimole)/X (millimoles)

X = 5.17 mmol/L

#### Q9. What is the pH of a buffer solution prepared with 0.05 M sodium borate and 0.005 M boric acid? (The pKa value of boric acid is 9.24]

pH = pKa + log salt/acid

= 9.24 + log 0.05/0.005

= 9.24 + log 10

= 9.24 + 1

= 10.24

#### Q10. What is the concentration, in milligrams per milliliter, of a solution containing 2 mEq of potassium chloride (KCl) per milliliter?

Molecular weight of KCl = 74.5

Equivalent weight of KCl = 74.5

1 mEq of KCl = 1⁄1000 × 74.5 g = 0.0745 g = 74.5 mg

2 mEq of KCl = 74.5 mg × 2 = 149 mg/mL.

#### Q11. How many grams each of dextrose and sodium chloride are used to prepare a 250-mL bag of D 5 1⁄2 NS for intravenous infusion?

250 mL × 0.05 (5% w/v) = 12.5 g dextrose, and

250 mL × 0.0045 (0.45% w/v) = 1.125 g sodium chloride

SOME COMMON INTRAVENOUS INFUSION SOLUTIONS

• 0.9% Sodium Chloride [NS (Normal Saline)]
• 0.45% Sodium Chloride [1⁄2 NS]
• 5% Dextrose in Water [D5W]
• 5% Dextrose in 0.9% Sodium Chloride [D5NS]
• 5% Dextrose in 0.45% Sodium Chloride  [D5 1⁄2 NS]

#### Q12. A physician orders midazolam hydrochloride (VERSED) 2 mg IV Stat. A pharmacist delivers a vial containing midazolam hydrochloride 5 mg/mL. How many milliliters should be administered?

5 mg/1 mL = 2 mg/X mL;

X = 0.4 mL

#### Q13. General guidelines in the treatment of severe diabetic ketoacidosis include an initial bolus dose of 0.1 to 0.4 unit of insulin/kg IVP, followed by an insulin drip. Calculate the bolus dosage range for a 200-lb patient.

200 lb / 2.2 lb/kg = 90.9 kg,

90.9 kg × 0.1 unit/kg = 9.09 units, and

90.9 kg × 0.4 unit/kg = 36.36 units.

#### Q14. Calculate the daily infusion volume of D10W to be administered to a neonate weighing 3 lb. 8 oz. on the basis of 60 mL/kg/day.

3 lb. 8 oz. = 3.5 lb. / 2.2 lb./kg = 1.59 kg or 1.6 kg

1.6 kg × 60 mL = 96 mL

#### Q15. If 10 mg of a drug are added to a 500-mL large-volume parenteral fluid; what should be the rate of flow, in milliliters per hour, to deliver 1 mg of drug per hour?

10 (mg)/1 (mg) = 500 (mL)/X (mL)

X = 50 mL per hour.