Dosage calculations for the CCMA

Write the unit beside every number as you go; each wrong option is built from a unit that got dropped.

1. Question 1

   The provider orders 0.25 g of an oral suspension. The label reads 125 mg per 5 mL. How many mL should be given?

   • A5 mL
   • B2 mL
   • C20 mL
   • D10 mL
   Answer & explanation

   Answer: D. 10 mL

   First convert 0.25 g to 250 mg, then divide by 125 mg and multiply by 5 mL: 250 ÷ 125 × 5 = 10 mL. Answering 2 mL divides the doses correctly but forgets that each 125 mg is in 5 mL, not 1 mL. Answering 5 mL gives only one labeled unit (125 mg), which is half the dose.

   • 5 mL delivers only one labeled unit, 125 mg — half of the 250 mg ordered.
   • 2 mL comes from 250 ÷ 125, forgetting that each 125 mg sits in 5 mL.
   • 20 mL doubles the dose, a slip such as reading 0.25 g as 500 mg.
   • Correct: 0.25 g = 250 mg; 250 ÷ 125 × 5 mL = 10 mL.

2. Question 2

   An order reads amoxicillin 0.5 g PO. The suspension on hand is 250 mg per 5 mL. How many mL should be given?

   • A2.5 mL
   • B5 mL
   • C10 mL
   • D2 mL
   Answer & explanation

   Answer: C. 10 mL

   Convert first: 0.5 g = 500 mg. Then 500 mg ÷ 250 mg × 5 mL = 10 mL. Stopping at 500 ÷ 250 gives 2, which is the number of 5-mL portions, not mL; inverting the ratio gives 2.5 mL; and 5 mL delivers only 250 mg, half the order.

   • 2.5 mL inverts the ratio (250 ÷ 500 × 5) and gives only 125 mg.
   • 5 mL holds just 250 mg, half the 500 mg ordered.
   • Correct: 0.5 g = 500 mg; 500 ÷ 250 × 5 mL = 10 mL.
   • 2 is the number of 5-mL portions, not the number of milliliters.

3. Question 3

   A medication is ordered 10 mg/kg/day divided q8h for a child weighing 30 kg. How many milligrams are given per dose?

   • A75 mg
   • B300 mg
   • C150 mg
   • D100 mg
   Answer & explanation

   Answer: D. 100 mg

   Daily dose = 10 mg/kg × 30 kg = 300 mg/day. q8h means 3 doses in 24 hours, so 300 ÷ 3 = 100 mg per dose. 300 mg is the whole day's amount given at once, 150 mg treats q8h as twice a day, and 75 mg divides by 4 as if it were q6h.

   • 75 mg divides the daily dose by 4, as if the order said q6h.
   • 300 mg is the total daily dose, not one of the three divided doses.
   • 150 mg treats q8h as twice a day; q8h means three doses in 24 hours.
   • Correct: 10 mg/kg × 30 kg = 300 mg/day; ÷ 3 doses = 100 mg each.

4. Question 4

   The provider orders heparin 7,500 units SubQ. The vial is labeled 10,000 units/mL. How many milliliters should be given?

   • A1.33 mL
   • B7.5 mL
   • C0.75 mL
   • D0.075 mL
   Answer & explanation

   Answer: C. 0.75 mL

   Divide the ordered dose by the concentration: 7,500 ÷ 10,000 = 0.75 mL. Answering 1.33 mL inverts the division (10,000 ÷ 7,500), a common error when the order is smaller than the vial strength. The answers 0.075 mL and 7.5 mL are decimal-place errors, and 7.5 mL is also far too much for a SubQ injection.

   • 1.33 mL flips the division (10,000 ÷ 7,500), a classic error when the order is below vial strength.
   • 7.5 mL is a decimal slip and far too large for any SubQ injection.
   • Correct: 7,500 ÷ 10,000 units/mL = 0.75 mL.
   • 0.075 mL moves the decimal one place too far and gives only 750 units.

5. Question 5

   An order reads 500 mg. The vial is labeled 250 mg/mL. How many milliliters should be drawn up?

   • A2 mL
   • B0.5 mL
   • C1 mL
   • D4 mL
   Answer & explanation

   Answer: A. 2 mL

   Divide the ordered dose by the concentration: 500 mg divided by 250 mg/mL equals 2 mL. Confirming unit consistency prevents dosing errors with parenteral medications.

   • Correct: 500 mg ÷ 250 mg/mL = 2 mL.
   • 0.5 mL inverts the division (250 ÷ 500) and gives only 125 mg.
   • 1 mL holds 250 mg, half of the ordered 500 mg.
   • 4 mL would deliver 1,000 mg, double the order.

6. Question 6

   The provider orders 1 g of a medication IM. It is supplied as 500 mg/mL. How many milliliters should be given?

   • A5 mL
   • B0.5 mL
   • C2 mL
   • D1 mL
   Answer & explanation

   Answer: C. 2 mL

   Convert first: 1 g = 1,000 mg, then 1,000 mg ÷ 500 mg/mL = 2 mL. Answering 0.5 mL inverts the division (500 ÷ 1,000). Answering 1 mL treats 1 g as if it were one unit of the supply, and 5 mL comes from a misplaced decimal.

   • 5 mL comes from a misplaced decimal and would deliver 2,500 mg.
   • 0.5 mL inverts the division (500 ÷ 1,000) and gives only 250 mg.
   • Correct: 1 g = 1,000 mg; 1,000 ÷ 500 mg/mL = 2 mL.
   • 1 mL treats 1 g as one unit of supply and delivers only 500 mg.

7. Question 7

   A provider orders 1.5 g of an enteric-coated drug. It is available as 500 mg tablets. How many tablets should be given, and how?

   • A3 tablets; crushed in applesauce
   • B2 tablets; swallowed whole
   • C2 tablets; crushed in applesauce
   • D3 tablets; swallowed whole
   Answer & explanation

   Answer: D. 3 tablets; swallowed whole

   Convert 1.5 g to 1,500 mg and divide by 500 mg to get 3 tablets. An enteric coating keeps the drug from dissolving in the stomach, so crushing it destroys that protection and can irritate the stomach lining. Two tablets comes from treating 1.5 g as 1,000 mg, and it delivers only two-thirds of the dose.

   • The count is right, but crushing destroys the enteric coating meant to protect the stomach.
   • Two tablets treats 1.5 g as 1,000 mg and gives only two-thirds of the dose.
   • Both parts are wrong: two tablets is underdosed, and crushing ruins the coating.
   • Correct: 1.5 g = 1,500 mg ÷ 500 mg = 3 tablets, swallowed whole to keep the coating intact.

8. Question 8

   A patient who weighs 154 lb is prescribed 2 mg/kg of an oral suspension. It is available as 100 mg per 5 mL. How many milliliters should be given?

   • A3.5 mL
   • B14 mL
   • C15.4 mL
   • D7 mL
   Answer & explanation

   Answer: D. 7 mL

   Convert the weight first: 154 ÷ 2.2 = 70 kg, then 70 × 2 mg = 140 mg, and 140 ÷ 100 × 5 = 7 mL. Answering 15.4 mL skips the weight conversion and uses 154 kg. Answering 3.5 mL treats the concentration as 100 mg per 2.5 mL, and 14 mL doubles the dose.

   • 3.5 mL treats the strength as 100 mg per 2.5 mL and gives only half the dose.
   • 14 mL doubles the correct volume and delivers 280 mg.
   • 15.4 mL skips the pound-to-kilogram conversion and uses 154 as if it were kg.
   • Correct: 154 ÷ 2.2 = 70 kg; × 2 mg = 140 mg; 140 ÷ 100 × 5 = 7 mL.

9. Question 9

   A provider prescribes 250 mcg of a medication for a patient. The medication is available as 0.5 mg per mL. How many milliliters should the medical assistant administer?

   • A0.25 mL
   • B5.0 mL
   • C0.5 mL
   • D1.0 mL
   Answer & explanation

   Answer: C. 0.5 mL

   Converting micrograms to milligrams: 250 mcg / 1,000 = 0.25 mg. Dividing the ordered dose by the concentration gives 0.25 mg / 0.5 mg per mL = 0.5 mL. Volumes of 0.25 mL, 1.0 mL, and 5.0 mL would deliver 0.125 mg, 0.5 mg, and 2.5 mg, none matching the ordered dose.

   • 0.25 mL delivers only 0.125 mg, half of the 250 mcg ordered.
   • 5.0 mL delivers 2.5 mg, ten times the ordered dose — a dangerous decimal error.
   • Correct: 250 mcg = 0.25 mg; 0.25 ÷ 0.5 mg/mL = 0.5 mL.
   • 1.0 mL delivers 0.5 mg, double the ordered dose.

10. Question 10

    A 44-lb child is prescribed 10 mg/kg/day of an antibiotic, divided into two equal doses. The medication is available as 250 mg per 5 mL of oral suspension. How many milliliters should the medical assistant give per dose?

    • A2 mL by mouth per dose
    • B1 mL by mouth per dose
    • C5 mL by mouth per dose
    • D4 mL by mouth per dose
    Answer & explanation

    Answer: A. 2 mL by mouth per dose

    Convert the weight: 44 lb / 2.2 = 20 kg. The daily dose is 20 x 10 = 200 mg, and each of two doses is 100 mg. Using 250 mg per 5 mL, the required volume is 100 / 250 x 5 = 2 mL. A 1 mL dose provides only 50 mg, 4 mL provides the entire daily dose at once, and 5 mL provides 250 mg, which exceeds the daily dose.

    • Correct: 44 lb = 20 kg; 200 mg/day ÷ 2 = 100 mg; 100 ÷ 250 × 5 = 2 mL.
    • 1 mL delivers only 50 mg, half of each divided dose.
    • 5 mL delivers 250 mg, more than the whole day's 200 mg in one dose.
    • 4 mL delivers 200 mg, the entire daily amount given at once.