Problem 21 - Calculate With Confidence

Question

Calculate the following dosages using the medication label or information provided. Label answers correctly: tabs, caps, mL. Answers expressed in milliliters should be rounded to the nearest tenth where indicated. Order: Phenobarbital elixir \(45 \mathrm{mg}\) p.o. b.i.d. Available: Phenobarbital elixir \(20 \mathrm{mg}\) per \(5 \mathrm{~mL}\) ________

Step-by-Step Solution

Answer

The required dosage is 11.3 mL per dose.

Step 1: Set Up the Dosage Calculation

You need to calculate the volume of elixir required to administer 45 mg of Phenobarbital. The concentration of the elixir is given as 20 mg per 5 mL.

Step 2: Calculate Amount Needed per Dose

Using the formula for dosage calculation: \( \text{Volume required} = \left(\frac{\text{Desired dose}}{\text{Concentration per mL}} \right) \times \text{Volume per concentration}\), substitute the given values: \[\text{Volume required} = \left(\frac{45 \text{ mg}}{20 \text{ mg}}\right) \times 5 \mathrm{~mL} \].

Step 3: Perform the Calculation

Calculate \( \left(\frac{45}{20}\right) \times 5 = 2.25 \times 5 = 11.25 \mathrm{~mL} \). Since the answer needs to be rounded to the nearest tenth, round 11.25 mL to 11.3 mL.

Key Concepts

Medication Measurement

Medication measurement is a critical skill in both nursing and pharmacy contexts. It involves understanding how to accurately administer medication to a patient, ensuring both the efficacy and safety of treatment.
In our example, we were required to determine how much of a liquid medication to provide to meet a prescribed dosage. Here, the prescription ordered Phenobarbital elixir 45 mg orally twice a day. The available elixir concentration was 20 mg per 5 mL.

This means:

• We need to convert the prescribed dose (45 mg) into the corresponding volume (in mL) that will deliver that dose.
• It involves interpreting the medication label which typically provides the concentration of medication in terms of mg per mL or per another volume measurement.

Such measurements require careful calculation to ensure the patient receives the correct amount, not too little or too much, which could be harmful.

Pharmaceutical Math

Pharmaceutical math deals with the calculations required for dosage and concentration, important for safety and effectiveness in medicine. In dosage calculation, you first need to understand the method of proportion.
The basic formula used here: \( \text{Volume required} = \left(\frac{\text{Desired dose}}{\text{Concentration per mL}} \right) \times \text{Volume per concentration}\), helps translate a prescribed dose into a specific volume.

This calculates the exact volume needed by:

• Dividing the desired dose (45 mg) by the concentration (20 mg), which gives the proportion of medication needed.
• Multiplying this fraction by the volume stated on the label (5 mL), delivering the actual liquid amount required to achieve the prescribed amount, 11.25 mL.

Math is not just about numbers but ensuring safe medication delivery by precisely measuring doses.

Pharmacology Education

Pharmacology education covers understanding drugs and their effects on the human body. It equips healthcare professionals with the necessary knowledge to execute their roles safely. Understanding the principles of pharmacology encompasses several areas:
For medication dosage, like the Phenobarbital order, it extends beyond just the math. It includes understanding:

• The pharmacokinetics (how the body affects a drug) and pharmacodynamics (how the drug affects the body) of medications.
• The potential effects, desired and adverse, and interactions with other medications or conditions.
• Proper technique in administering the medication as seen in our calculation, which assures the correct, rounded dose of 11.3 mL is given.

Pharmacology education forms a comprehensive foundation, ensuring that healthcare professionals can make informed, evidence-based decisions about patient medication management.