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Practice problems · Injectables · 5 worked

Injectable dosage calculation practice problems

An injectable problem asks how many milliliters to draw up from a vial labeled by concentration, such as 10 mg per 1 mL or 300 mg per 3 mL. The volumes are often under 1 mL, where a decimal point one place out turns 0.5 mL into 5 mL.

The rounding rule on this page

Every answer here is rounded once, at the end, under one stated rule: nearest tenth, half rounds up, except tablets and capsules, rates in milliliters per hour and drip rates in drops per minute, which go to the nearest whole number, half rounds up. Your program's rule may differ, and on an exam it is the one that counts.

Work each problem on paper first, then open its solution. Each one is one of the 20 problems in DoseReady's Injectable family, with the numbers the app drew for it.

No licensed clinician has reviewed the problem set. Where a problem and its source disagree, trust the source and what your program teaches.

Problem 1 of 5

The order reads 40 mg of enoxaparin subcutaneously once daily. The multidose vial on hand is labeled 300 mg per 3 mL. How many milliliters are drawn up?

Show the worked solution

Dimensional analysis

40 × 3 ÷ 300 = 0.4

Ratio and proportion

  1. 300 mg is to 3 mL as 40 mg is to x

    40 × 3 ÷ 300 = 0.4

    x = 0.4 mL

Formula method

D (desired)
40 mg
H (have)
300 mg
Q (quantity)
3 mL

D ÷ H × Q

40 × 3 ÷ 300 = 0.4

The working comes to
0.4 mL
The answer under the stated rule
0.4 mL
Nearest tenth, half rounds up.

What each slip gives here

  • Decimal point one place out4 mL
  • Conversion factor inverted4,000 mL
  • Conversion skipped40 mL
  • Rounded to the wrong precision0.5 mL

“Rounded to the wrong precision” is the same working rounded to some other step, such as a half, a quarter or a hundredth, or left unrounded.

What this problem is built from

Problem 2 of 5

The order reads 10 mg of morphine intramuscularly now. The vial on hand is labeled 10 mg per 1 mL. How many milliliters are drawn up?

Show the worked solution

Dimensional analysis

10 × 1 ÷ 10 = 1

Ratio and proportion

  1. 10 mg is to 1 mL as 10 mg is to x

    10 × 1 ÷ 10 = 1

    x = 1 mL

Formula method

D (desired)
10 mg
H (have)
10 mg
Q (quantity)
1 mL

D ÷ H × Q

10 × 1 ÷ 10 = 1

The working comes to
1 mL
The answer under the stated rule
1 mL
Nearest tenth, half rounds up.

What each slip gives here

  • Decimal point one place out10 mL or 0.1 mL
  • Conversion factor inverted100 mL

What this problem is built from

Problem 3 of 5

The order reads 1.2 mg of naloxone by intravenous push now. The multidose vial on hand is labeled 4 mg per 10 mL. How many milliliters are drawn up?

Show the worked solution

Dimensional analysis

1.2 × 10 ÷ 4 = 3

Ratio and proportion

  1. 4 mg is to 10 mL as 1.2 mg is to x

    1.2 × 10 ÷ 4 = 3

    x = 3 mL

Formula method

D (desired)
1.2 mg
H (have)
4 mg
Q (quantity)
10 mL

D ÷ H × Q

1.2 × 10 ÷ 4 = 3

The working comes to
3 mL
The answer under the stated rule
3 mL
Nearest tenth, half rounds up.

What each slip gives here

  • Decimal point one place out30 mL or 0.3 mL
  • Conversion factor inverted0.5 mL
  • Conversion skipped1.2 mL

What this problem is built from

Problem 4 of 5

The order reads 25 mg of promethazine by deep intramuscular injection. The single-dose vial on hand is labeled 50 mg per 1 mL. How many milliliters are drawn up?

Show the worked solution

Dimensional analysis

25 × 1 ÷ 50 = 0.5

Ratio and proportion

  1. 50 mg is to 1 mL as 25 mg is to x

    25 × 1 ÷ 50 = 0.5

    x = 0.5 mL

Formula method

D (desired)
25 mg
H (have)
50 mg
Q (quantity)
1 mL

D ÷ H × Q

25 × 1 ÷ 50 = 0.5

The working comes to
0.5 mL
The answer under the stated rule
0.5 mL
Nearest tenth, half rounds up.

What each slip gives here

  • Decimal point one place out5 mL or 0.1 mL
  • Conversion factor inverted1,250 mL
  • Conversion skipped25 mL
  • Rounded to the wrong precision1 mL

“Rounded to the wrong precision” is the same working rounded to some other step, such as a half, a quarter or a hundredth, or left unrounded.

What this problem is built from

Problem 5 of 5

The order reads 5,000 units of heparin subcutaneously every twelve hours. The vial on hand is labeled 10,000 units per 1 mL. How many milliliters are drawn up?

Show the worked solution

Dimensional analysis

5,000 × 1 ÷ 10,000 = 0.5

Ratio and proportion

  1. 10,000 units is to 1 mL as 5,000 units is to x

    5,000 × 1 ÷ 10,000 = 0.5

    x = 0.5 mL

Formula method

D (desired)
5,000 units
H (have)
10,000 units
Q (quantity)
1 mL

D ÷ H × Q

5,000 × 1 ÷ 10,000 = 0.5

The working comes to
0.5 mL
The answer under the stated rule
0.5 mL
Nearest tenth, half rounds up.

What each slip gives here

  • Decimal point one place out5 mL or 0.1 mL
  • Conversion factor inverted50,000,000 mL
  • Conversion skipped5,000 mL
  • Rounded to the wrong precision1 mL

“Rounded to the wrong precision” is the same working rounded to some other step, such as a half, a quarter or a hundredth, or left unrounded.

What this problem is built from

Practice under your own program's rules

In DoseReady you enter your program's passing score, notation and rounding rule once. Every answer is graded under that rounding rule, and each worked solution is written in your notation where the problem allows it.

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