A nurse is to give a 150 mg injection from a vial containing 500 mg diluted in 5 ml. How many ml will she inject?

Appeared in: IGIMS Staff Nurse - 2018

Explanation

The question requires the nurse to calculate the correct volume of medication to administer based on the prescribed dose and the available concentration.
The standard formula for dosage calculation is (Dose Desired / Dose on Hand) × Quantity on Hand.
Plugging in the given values: (150 mg / 500 mg) × 5 ml.
First, divide 150 by 500, which equals 0.3.
Then, multiply 0.3 by the volume of 5 ml, which results in 1.5 ml.
Thus, 1.5 ml is the correct volume to inject to deliver a 150 mg dose.

Option A: Administering 1 ml would result in an incorrect and lower dose. 1 ml of this solution contains 100 mg of the drug (500 mg / 5 ml = 100 mg/ml), which is less than the prescribed 150 mg.
Option C: Administering 2 ml would result in an overdose. 2 ml of this solution contains 200 mg of the drug (100 mg/ml × 2 ml), which is more than the prescribed 150 mg.
Option D: Administering 2.5 ml would result in a significant overdose. 2.5 ml of this solution contains 250 mg of the drug (100 mg/ml × 2.5 ml), which is much higher than the prescribed 150 mg.

Clinical Relevance

Nursing practice connection: Knowing Medication Dosage Calculation helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Accurate dosage calculation is a fundamental and critical nursing skill to ensure patient safety. Errors can lead to underdosing (ineffective treatment) or overdosing (toxicity and adverse effects).
Nurses must always perform the 'three checks' and adhere to the 'rights of medication administration' before giving any drug. Double-checking calculations, especially for high-alert medications, is a crucial safety measure.
What if the medication was available as 500 mg in a 10 ml vial? The concentration would be 50 mg/ml. To give 150 mg, the nurse would need to inject 3 ml (150 mg / 50 mg/ml).

How to Approach the Question

First, identify the key pieces of information given in the question: the desired dose, the available dose (dose on hand), and the volume the available dose is in (quantity on hand).
Desired Dose = 150 mg
Dose on Hand = 500 mg
Quantity on Hand = 5 ml
Recall or look up the standard formula for dosage calculation: (Desired / Have) × Quantity.
Substitute the values into the formula: (150 mg / 500 mg) × 5 ml.

Concept Tested & Keywords

QLTdMPSvptNVHYvwcZKwfB

E6 Pharmacology Nurses Shanbhag 3e p. 55-57

E6 Nursing Fundamentals Taylor p. 848-850

Practise the full IGIMS Staff Nurse - 2018

Attempt every question from this paper in a timed mock, then review the full solution for each one.