Intro to Dosage, Oral & Parenteral Dosage Calcualtions Module

Module Overview

This module begins our multi-week journey exploring dosage calculations!  YAY!

We will first look at some foundational elements that will be necessary for understanding medication dosage orders, including abbreviations, the 24-hour clock, medication labels,  and administration vehicles/equipment. 

We'll then turn our attention to dosage calculations, which we will see are just conversion problems.  

Before we complete any mathematical calculations, it will be absolutely essential that we stop to consider what a medication order is telling us, and how the patient is expected to receive the medication -- by mouth?  Through an injection in their vein or muscle? By an eye drop? Any so forth.  

Once we can make sense of the clinical situation that is taking place, then we can focus on the desired dose (what the patient must receive), the strength of the medication that is available, and the tools that are available for administering the medication.  This will be true for the next few weeks, but this week our focus will be clinical situations involving  oral dosage (medication given by mouth) and parenteral dosage (usually injections, but other non-oral routes are possible as well). 

Be sure to download and print the module guide to help you keep track of your notes and completed work. 

Module outcomes:

• • Interpret medication dosage orders, abbreviations, and drug labels.

  • Convert time between the 12-hour and 24-hour clocks.

  • Discuss the precision of dosage vehicles. 

  • Calculate oral dosage.

  • Calculate parenteral dosage and select the appropriate tool for administration.  

  • Calculate the amount of medication prepared for administration.

So, if you are given a medication label, you should be able to answer the following questions:

1. What is the brand name? What is the generic name?

2. How is the drug being administered (orally, ID, IM, IV, etc)?  (*** VERY IMPORTANT *** ) 

3. What is the contents of the container (tablets, capsules, liquid for injecting, powder for reconstitution, etc.)?

4. What is the dosage strength (concentration)?

5. Is there a recommended amount to administer (safe instructions)?

6. Are there any important storage instructions?

It should be clear from the video above that there is more information on these labels, but when we are tasked with calculating the appropriate amount to administer to patients, these are the elements that we will focus the most amount of attention on.

When medication orders are given, there is usually information pertaining to when and how often the medication should be given. For example, the order might state that the medication should be given at 1100.

However, you might be asking, does 1100 mean 11:00 am or 11:00 pm? This is the problem with using a 12-hour clock with medication orders; there is a chance that a time might be interpreted incorrectly (for example, medication given at 9:00 am instead of 9:00 pm).

Thankfully there is an easy way to avoid this:  the 24-hour clock -- as referred to as military time.  

Here is a video I created going over the 24-hour clock and how we can convert between standard times and those in military time:

Some take-aways:

1. Orders will not use the 12-hour clock (or “Civilian” time). This is to prevent confusion in the cases when someone accidentally forgot to include the AM or PM.

2. You can think of the correct time using the 24-hour clock as the number of hours and minutes that have elapsed so far that day.

3. Anything after 12:59 PM will be different using the 24-hour clock — this is because with the 12-hour clock after 12:59PM, we circle back to 1, 2, and so on. At the usual 1:00 PM time, we know that 13 hours have passed in the day, so 1300 would be the correct way to write this time using the 24-hour clock.  Many videos suggest you add “1200” to the PM time, but be careful.. 12:36PM would be 1236. 

If you’re still a little unsure about military time, I have put together a few additional videos below that you can view. Or, if you think you’re ready for practice, you can go to this link (http://www.aaamath.com/meats2m.htm) for information and practice problems (towards the bottom of the page)  

We are now ready to calculate some dosage!  As we will see, a dosage calculation is simply a conversion problem, where we have to convert the amount of medication that patient needs into an appropriate unit (such as tablets, mL, capsules, or some other unit). 

Let's start with an example and then practice a few problems -- follow along with the video below. 

According to your textbook, the term parenteral refers to those medications that are not taken by mouth — that is, it does not pass through the digestive tract. This includes medications that are administered via injection, patch, ear drop, rectum, and more. However, our focus this week will be on injections.

We should already be familiar with the abbreviations IM, IV, and ID from up above -- these abbreviations all indicate a type of injection (as you can see below)

Let's walk through a few examples in the video below. 

One thing I forgot to mention in the last example in the video above:  We would have to dilute the azithromycin even more before administering it to the patient.  We would likely dilute this in a 500 mL or 250 mL bag of fluid to be given as an infusion.  We will see this a bit more next week!

With that being said, I hope the two calculations made sense.  You'll notice that the mathematics and reasoning is identical to what we saw with oral dosage calculations, but we also had to "prepare" the medication with the appropriate syringe. 

Let's move on to a few more examples. 

Try the practice problems below, and if you need additional practice, please see the "Parenteral Dosage" unit in your e-text.  There are plenty more examples in there!

We are given five dosage related problems. Complete these calculations on your module guide to assess your understanding.  (Recommendation: Try to complete these without your notes first).  Remember to show all of your work!

Check your solutions with the link document at the end. 

*Optional Practice*

For more practice with the "prepared dosage" problems, you can access an optional worksheet below:

• Prepared Dosage Worksheet

• Solutions Document (NOW AVAILABLE)