The doctor orders Zofram (ondansetron HCl) 8 mg PO t.i.d. The pharmacy sends a 100 ml bottle, labeled 4 mg/teaspoon. How many ml should be given for each dose?

Appeared in: GMCH Chandigarh - 2019

Explanation

The prescribed dose is 8 mg of Ondansetron.
The medication is supplied at a concentration of 4 mg per teaspoon.
A standard medical conversion is 1 teaspoon = 5 mL, making the concentration 4 mg/5 mL.
Using the dosage calculation formula (Dose Ordered / Dose on Hand) × Quantity: (8 mg / 4 mg) × 5 mL results in 10 mL.
Administering 10 mL of the solution provides the correct 8 mg dose.

Option A: Administering 2 mL of a 4 mg/5 mL solution would deliver only 1.6 mg of the medication, which is a significant underdose.
Option B: Administering 8 mL of a 4 mg/5 mL solution would deliver 6.4 mg of the medication, which is less than the prescribed dose of 8 mg.
Option C: This is the volume of one teaspoon, which contains only 4 mg of the medication. This is half of the required dose.

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 nursing responsibility to ensure patient safety and prevent medication errors, which can have serious adverse effects.
Nurses must be proficient in converting between household and metric units, as prescriptions may use either system, but administration should always be done with precise, calibrated metric devices.
What if? If the medication was labeled 4 mg/mL instead of 4 mg/teaspoon, the calculation would be (8 mg / 4 mg) x 1 mL = 2 mL. This highlights the critical importance of carefully reading the 'quantity' part of the concentration on the label.

How to Approach the Question

First, identify the question as a dosage calculation problem requiring you to find the volume (mL) to administer.
Extract the key values from the problem: the 'Desired' dose (D) is 8 mg, and the 'Have' dose (H) is 4 mg.
Identify the 'Quantity' (Q) associated with the 'Have' dose, which is 1 teaspoon. Recognize that the final answer must be in mL, so a conversion is necessary.
Recall or look up the standard conversion: 1 teaspoon = 5 mL.
Apply the universal dosage calculation formula: (Desired / Have) × Quantity.
Substitute the values into the formula: (8 mg / 4 mg) × 5 mL.

Concept Tested & Keywords

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E6 Nursing Fundamentals Potter Perry 12e Part 3 p. 141-143

E6 Nursing Fundamentals Taylor p. 848-850

Practise the full GMCH Chandigarh - 2019

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