A patient is prescribed 250 mg of an antibiotic. The medication is available as 1 gram in 10 ml. How many ml should the nurse administer?

Appeared in: DSSSB 6 September 2024

Explanation

The core of this question is applying the 'Desired over Have' formula for medication dosage.
A critical first step is unit conversion. The prescribed dose (250 mg) and the available dose (1 g) must be in the same unit. Converting 1 gram to 1000 mg is necessary.
The formula is (Desired Dose / Dose on Hand) × Quantity.
Plugging in the values: (250 mg / 1000 mg) × 10 ml.
The calculation simplifies to 0.25 × 10 ml, which equals 2.5 ml.

Option B: This is an incorrect calculation. It may result from dividing 1000 by 250 (which is 4) and then making another error, or simply misplacing the decimal. For example, (250/1000) * 20 would equal 5.
Option C: This result might occur if the nurse incorrectly calculates (250/1000) and gets 0.05, then multiplies by 10. Or, if they calculate 250/1000 = 0.25 but forget to multiply by the quantity (10 ml) and make a decimal error.
Option D: This is a calculation error. There is no standard miscalculation that consistently leads to this answer, suggesting a random math mistake.

Clinical Relevance

Nursing practice connection: Use the key finding related to Medication Dosage Calculation to guide bedside assessment, documentation, and the next nursing action.
Accurate dosage calculation is a fundamental nursing skill and a critical component of the 'Right Dose' within the Rights of Medication Administration, directly impacting patient safety.
Medication errors, often stemming from incorrect calculations or unit conversions, are a leading cause of preventable harm in healthcare. Always double-check calculations, especially for high-risk drugs.
What if? If the available medication was 1 gram in 4 ml, the calculation would change to (250 mg / 1000 mg) * 4 ml = 1 ml. The quantity of the diluent is as important as the strength of the drug.

How to Approach the Question

First, identify the three key pieces of information given in the problem: the Desired dose (what's ordered), the Have dose (what's available), and the Quantity (the volume the 'Have' dose is in).
Next, check if the units for the 'Desired' and 'Have' doses are the same. If not (like mg and grams in this case), convert one to match the other. It's usually easiest to convert the larger unit to the smaller one (grams to mg).
Apply the standard dosage calculation formula: (Desired / Have) × Quantity.
Substitute the numbers into the formula and solve for the unknown.
Finally, critically evaluate your answer. Does it make sense? For example, since 250 mg is a quarter of 1000 mg, the volume should be a quarter of 10 ml, which is 2.5 ml. This estimation helps confirm your calculation.

Concept Tested & Keywords

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E6 Nursing Fundamentals Potter Perry 12e Part 3 pp. 141-143, 142-144

E6 Nursing Fundamentals Taylor p. 848-850

Practise the full DSSSB 6 September 2024

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