Accurate medication dosage calculation is crucial in nursing and healthcare, ensuring patient safety and effective treatment. This article will guide you through solving liquid oral suspension dosage problems using the ratio and proportion method, a fundamental technique in medication administration.
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Understanding the Ratio and Proportion Method
The ratio and proportion method is a structured approach that involves setting up known and unknown ratios to determine the correct medication dosage. Alternative methods include dimensional analysis or the desired over have formula method. However, ratio and proportion remain widely used due to their clarity and ease of application.
Whenever you’re setting up ratio and proportion, you’re creating ratios that, when solved, should be proportionate and equal to each other. You create a known ratio and an unknown ratio. The known ratio consists of the dose you have over the volume you have, because this is the information available. This is then set equal to the dose ordered over X, which represents the unknown value we are solving for. This unknown value is what will be administered.
Practice Problem 1
A patient is prescribed 5,000 micrograms (mcg) of a medication to be taken by mouth twice a day (BID). The available suspension contains 3 milligrams (mg) per milliliter (mL). How many mL/dose will be administered?
To solve, we need to create a known ratio using the supplied dose and volume (3 mg per 1 mL) and set it equal to the unknown ratio representing the ordered dose (5,000 micrograms over X mL).
Before solving for X by cross-multiplying, it’s essential to ensure that units of measurement match. The order is given in micrograms, while the supply is labeled in milligrams. Since 1 mg equals 1,000 mcg, converting 5,000 mcg to mg results in 5 mg.
Substituting this value into the equation, we now have: 3mg over 1 mL equals 5 mg over x
To find X, we cross multiply: 3x = 5
Solving for X requires dividing both sides by 3. 5 divided by 3 equals 1.66666 (repeating)
Rounding to the nearest tenth, the correct dose per administration is 1.7 mL/dose. To verify accuracy, we substitute this value back into the proportion and confirm that both sides remain equal.
Practice Problem 2
A patient is prescribed 1,000 mg of medication by mouth daily. The available suspension contains 2 grams (g) per 10 mL. How many tsp/dose will you administer?
The problem involves an order for 1,000 mg by mouth daily, with a supplied bottle labeled 2 grams per 10 mL.
The first step is to set up the known ratio as 2 g / 10 mL and the unknown ratio as 1,000 mg / X mL.
Here, the units need to be converted to match. Since 1,000 mg is equal to 1 g, the unknown ratio is rewritten as 1 g / X mL.
Additionally, the volume must be converted to teaspoons, and since 10 mL equals 2 teaspoons, the new known ratio becomes 2 g / 2 tsp.
Now, setting up the proportion as 2 g / 2 tsp = 1 g / X tsp, cross multiplying results in 2X = 2. Solving for X, dividing by 2 on both sides gives X = 1 tsp per dose.
Practice Problem 3
A patient is prescribed 500 mg of medication by mouth every 8 hours. The available suspension contains 150 mg per 5 mL. How any mL/day will be administered?
For the final example, an order is given for 500 mg by mouth every 8 hours. The supplied bottle is labeled 150 mg per 5 mL, and the goal is to determine how many milliliters per day are required.
The known ratio is 150 mg / 5 mL, while the unknown ratio is 500 mg / X mL. Since the units already match, cross multiplying results in 150X = 500 × 5, which simplifies to 150X = 2,500. Dividing by 150 gives X = 16.666666 (repeating) mL per dose…do NOT round just yet.
Since the medication is administered every 8 hours, determining the total daily amount requires calculating the number of doses per day. Since 24 hours divided by 8 hours per dose equals 3 doses per day, multiplying 16.6666666 (repeating) mL by 3 results in 50 mL per day.
For further practice, be sure to check out this liquid oral suspension dosage calculation quiz.
