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Dosage Calculation: Tablets – Ratio and Proportion (Nursing)

by Rhonda Lawes

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      Slides Nursing Dosage Calculation Ratio Proportion Medications.pdf
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      Cheat Sheet Understanding Ratios.pdf
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    00:00 Hi, welcome to our dosage calculation video series.

    00:04 Now in this portion, we're gonna take a look at what you've learned from about ratio and proportion and talk about how it actually applies to medication dosages.

    00:13 So let's do a quick review from our other portions.

    00:16 Alright, a ratio represents just a relationship between two numbers.

    00:21 Now there's my favorite Schnauzer in the world, Harley.

    00:24 Remember that's 3 tennis balls to 4 Harleys, which I can hardly imagine living with 4 of her but we've got 3 to 4.

    00:32 We take that same relationship, rewrite it as a fraction, that's 3/4, with 3 being the numerator, 4 being the denominator.

    00:42 Now we take the same thing and you would write it as the proportion. We've got 3:4.

    00:47 Each one of those three examples are communicating the same thing just using different symbols.

    00:54 So proportions represent two ratios or fractions that are equal.

    00:59 Proportions are solved by multiplying the means, the numbers in the middle, and the extremes.

    01:04 So we've color coded for you here just as a quick reminder.

    01:08 We've got the extremes, they're in that kind of pinkish color and you've got that means that are in the flesh colors.

    01:14 Remember, always double check your work.

    01:17 So when you get what x equals, you wanna go back and plug it into the formula to make sure your answer is correct.

    01:24 Again, even in practice, I make sure to have someone else check my math just to be extra sure.

    01:30 An extra safeguard to make sure I'm giving an appropriate dosage to my patient.

    01:35 Okay, so let's take one acetaminophen.

    01:38 Now this one you may know by the brand name of Tylenol but acetaminophen extra strength, 500 mg per tablet.

    01:46 So we know that one tablet has 500 mg. That's no different than 3 tennis balls and 4 Harleys. 1 tab, 500 mg.

    01:57 Now you turn that into a fraction: 1 tab, that's the numerator, 500 mg is the denominator.

    02:05 Okay, now I know you're thinking, "Wow, this is kind of moving slow." It always will in the beginning with me because I know the anxiety that's attached to math.

    02:15 So I wanna make sure you're really solid on this concepts as we move through the next steps.

    02:20 Now the order reads acetaminophen po 750 mg every 6 hours.

    02:28 You have acetaminophen 500 mg/tablet.

    02:33 Okay, acetaminophen po, that means per os, it stands for the Latin "by mouth" so that's what po means.

    02:42 750 mg is the amount the physician has ordered of Tylenol or acetaminophen they should receive every six hours.

    02:52 Now you might often see "q" instead of the word "every", you might see a lower case Q.

    02:57 That also means every or each six hours.

    03:00 So this is what the physician wants, 750 mg every six hours.

    03:06 What I have on hand is 500 mg per tablet. So 1 tab equals 500 mg.

    03:15 So how do you solve ratio problems? Well, hopefully these steps look familiar to you.

    03:20 You identify the known ratio and the unknown ratio.

    03:24 You set up the proportions, cross multiply and solve for x then check the answer by plugging the result into the unknown ratio.

    03:32 Remember the unknown ratio is the ordered amount by the physician.

    03:37 The known ratio is the medication that we have, remember? 1 tablet has 500 mg.

    03:43 We're gonna try and figure out how many tablets it takes to make the unknown ratio, the 750 mg.

    03:50 Now I know you can probably do that math in your head but that's why we pick an example like this to show you how and what the process is.

    03:59 So it's not so much can you do the math in your head once you didn't understand the process as we walk through it. So we're gonna try it with x.

    04:06 First of all, you set this up 1 tab is 500 mg, I'm trying to figure out how many tabs equal 750 mg.

    04:16 I'm gonna multiply the extremes and then the means that involves cross multiplication.

    04:22 So you -- we always try to put the x on the left side, just take that for what it is, it helps keep things in order.

    04:29 So we put the 500x on one side of the equation equals 750.

    04:35 Now we're gonna solve for x. X needs to stand by itself.

    04:39 So in that step, we always divide the equation on both sides by the number that's in front of the x.

    04:46 So 500x divided by 500, 750 also divided by 500.

    04:53 Whatever I do to the left side, I need to do exactly the same thing to the right side.

    04:58 Now the x that's remaining is x equals 1.5.

    05:03 Now 500x divided by 500 is 1x but you can always just write x, you don't have to put the 1 in front of it.

    05:11 Now we've got 500 into 750, and we've got 1 and 1/2 times.

    05:17 So x equals 1 and 1/2. Now stop and think for just a minute.

    05:22 First of all, before we check our work, does that make sense? With a tablet, could I come up with 1 and 1/2 tablets? Yes. That's reasonable.

    05:33 Can I come up with 1.134567 tablets? No. I can't break a tablet down to those small amounts.

    05:41 I can do a half a tablet but I can't do tiny hundreds of a decimal place of a tablet.

    05:47 Now if I was figuring out IV rates, that I can get down very precise depending on the type of pump that I have available.

    05:55 If it's a liquid measurement, I can use a cup, a little medicine cup that goes up to 30 ml.

    06:01 So I can do it pretty closely by 4 or 5 ml by 5 ml.

    06:06 If I need a more precise liquid measurement, then I would draw the liquid up in a syringe at whatever the right amount of units are that I can do that with.

    06:16 So you always to think, "Hey, what format is the medication in? And does this make sense to give one and a half tabs?" Absolutely.

    06:24 Now, that fifth step is to always check your work. So go back and plug x back in.

    06:31 So you'll see we have 1 tab divided by 500, 1 and 1/2 by 750.

    06:36 And we've plugged 1 and 1/2 in instead of where x was. We do the cross multiplication.

    06:42 We come up with 1 times 750 equals 1 and 1/2 times 500 exactly.

    06:48 They're both 750 and 1 and 1/2 times 500 is also 750 so we know that the safe dosage is 1 and 1/2 tabs of acetaminophen for this patient.

    06:59 How often? Right, every 6 hours. Good job. 1 and 1/2 is the correct dose for our patient.


    About the Lecture

    The lecture Dosage Calculation: Tablets – Ratio and Proportion (Nursing) by Rhonda Lawes is from the course Dosage Calculation (Nursing).


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    Author of lecture Dosage Calculation: Tablets – Ratio and Proportion (Nursing)

     Rhonda Lawes

    Rhonda Lawes


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