Pharmacy Aliquots MADE EASY

Summary

This video from the Pharmacist Academy provides a detailed guide on how to perform pharmacy aliquots for both solids and liquids. The host explains essential concepts like sensitivity and minimum weighable quantity (MWQ) to ensure accuracy in compounding medications. Using examples, the video demonstrates how to calculate and prepare aliquots when the required drug amount is below the MWQ. The host also presents a bonus question on capsule compounding and explains the process step by step, making the video a practical resource for pharmacy students preparing for exams.

Takeaways

• 💊 Compounded pharmaceutical products must have a low percentage of error to ensure accuracy in weighing and measuring during medication compounding.
• ⚖️ Sensitivity refers to the lowest amount a balance can weigh accurately, while the minimum weighable quantity (MWQ) includes the percentage of error.
• 📏 According to the U.S. Pharmacopeia, balances must have a 5% or lower rate of error, ensuring accuracy at least 95 out of 100 times.
• 🧪 Aliquots are used when the required amount of a drug is below the MWQ, allowing accurate measurement by creating a dilution of the drug with an inactive ingredient.
• 🔢 The aliquot method involves using the ratio of the amount needed over the MWQ and multiplying it to create a larger weight for accurate measurement.
• 📊 Example 1: To weigh 10 mg of a drug when the MWQ is 20 mg, multiply both sides by 2, yielding a 40 mg total dilution containing 20 mg of the drug and 20 mg of lactose.
• 💡 Example 2: For 95 mg of a drug with a 100 mg MWQ, multiply by 2 to get 190 mg total, consisting of 190 mg drug and 10 mg lactose.
• ⚗️ Example 3: To measure 3 ml of a drug when the minimum measurable quantity is 5 ml, create a dilution by multiplying by 2, making a 10 ml total containing 3 ml of the drug and 2 ml of water.
• 📦 For capsule preparations, apply the aliquot method when the total weight is below the MWQ, such as with Drug B in the example where an aliquot is created with drug and lactose.
• 📝 In capsule prescriptions, ensure total powder weight calculations consider both active ingredients and any fillers like lactose to meet the capsule's total required weight.

Q & A

What is the minimum weighable quantity (MWQ) in pharmacy compounding?

The minimum weighable quantity (MWQ) is the lowest amount that can be accurately weighed by a balance, considering the allowed percentage of error. It ensures that measurements below the MWQ are not used due to the risk of inaccuracy.

Why is sensitivity important in pharmaceutical compounding?

Sensitivity is important because it defines the smallest amount a balance can weigh accurately. Weighing anything below the sensitivity level can lead to inaccuracies, which is critical when compounding medications with precise dosages.

How is the minimum weighable quantity (MWQ) different from sensitivity?

While sensitivity refers to the smallest amount a balance can measure, MWQ takes into account the percentage of error, adjusting the minimum weight to ensure acceptable accuracy in pharmaceutical compounding.

What is an aliquot, and how is it used in pharmacy?

An aliquot is a portion of a larger sample, often used in pharmacy to measure a small amount of a substance by diluting a larger quantity. This ensures accuracy when the required amount is below the MWQ.

How do you calculate the new aliquot weight in pharmacy compounding?

To calculate the new aliquot weight, you multiply the amount needed by a factor that will bring the total to the MWQ or higher. This allows you to weigh out a portion that meets the MWQ requirements while maintaining the correct dosage.

What is the procedure if the drug quantity you need to weigh is below the MWQ?

If the drug quantity is below the MWQ, you need to create a dilution using the aliquot method. You divide the amount needed by the MWQ and multiply both the amount and the total weight by a factor to achieve the required dilution.

Can you provide an example of calculating an aliquot for a drug with a required quantity below the MWQ?

Yes, if you need to weigh 10 mg of a drug but the MWQ is 20 mg, you create a dilution. Using a multiplier of 2, you create a total of 40 mg, with 20 mg of active drug and 20 mg of lactose. You would weigh out 20 mg of this mixture, which contains the required 10 mg of the active drug.

How do you apply the aliquot method when measuring liquids in pharmacy compounding?

For liquids, the aliquot method follows the same concept. For example, if you need to measure 3 mL of a liquid but the minimum measurable quantity (MMQ) is 5 mL, you create a dilution using a larger volume (e.g., 6 mL of the drug and 4 mL of water), then measure the MMQ of 5 mL, which contains the 3 mL of the active ingredient.

How do you calculate the total amount of active ingredients and lactose in a compounded prescription?

To calculate the total active ingredients and lactose in a prescription, you sum the required amounts for each drug, taking into account any aliquot adjustments. Then, you subtract the active ingredient weight from the total powder weight to determine the amount of lactose required.

What is the importance of accuracy and error minimization in pharmaceutical compounding?

Accuracy and error minimization are crucial in pharmaceutical compounding to ensure that medications are safe and effective. Compounded products must have a low percentage of error, as inaccuracies in dosage could lead to ineffective treatment or harmful side effects.