500 mg of a drug is order. It is supplied in tablets of 1gram per tablet. How many tablets should be administered?

Appeared in: OSSSC Nursing Officer-2021

Explanation

The calculation requires converting the available dose from grams (g) to milligrams (mg) to match the unit of the ordered dose.
The conversion factor is 1 gram = 1000 milligrams.
Using the standard dosage formula (Dose Ordered / Dose on Hand) × Quantity, the calculation is (500 mg / 1000 mg) × 1 tablet.
This simplifies to 0.5 × 1, which equals 0.5 tablets.

Option B: Administering 1 tablet would mean giving 1 gram (1000 mg) of the drug, which is double the prescribed dose of 500 mg. This error occurs by ignoring the difference between the ordered dose and the dose on hand.
Option C: This is a calculation error. Administering 1.5 tablets would result in a dose of 1500 mg, which is a significant overdose (three times the prescribed amount).
Option D: This is a calculation error, likely from incorrectly dividing the dose on hand by the ordered dose (1000 mg / 500 mg = 2). This would result in an administration of 2000 mg, a four-fold overdose.

Clinical Relevance

Nursing practice connection: Knowing Drug Dosage Calculation helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Accurate dosage calculation is a fundamental nursing responsibility to ensure patient safety and prevent medication errors, which can have severe or fatal consequences.
The 'Six Rights of Medication Administration' (Right Patient, Right Drug, Right Dose, Right Route, Right Time, Right Documentation) must always be followed, with dose calculation being a key part of ensuring the 'Right Dose'.
Always double-check calculations, especially when unit conversions are involved. If unsure, have another nurse verify the calculation before administering the medication.

How to Approach the Question

First, identify the key pieces of information: the dose ordered (D), the dose on hand (H), and the quantity or form it comes in (Q).
Next, check if the units for the ordered dose and the on-hand dose are the same. In this case, they are not (mg vs. g).
Convert one of the units to match the other. It's often easiest to convert the larger unit to the smaller unit (1 g = 1000 mg).
Apply the standard dosage calculation formula: (D / H) x Q.
Substitute the values into the formula: (500 mg / 1000 mg) x 1 tablet.
Calculate the final answer and select the corresponding option.

Concept Tested & Keywords

QYk72QQmoFl0HlkMtAprPe

E6 Pharmacology Nurses Shanbhag 3e pp. 51-53, 52-54

E6 Nursing Fundamentals Taylor p. 848-850

Practise the full OSSSC Nursing Officer-2021

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