Dosage Calculation

by Jill Beavers-Kirby

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    00:00 Hi! My name is Jill Beavers-Kirby, and today, we're going to be talking about some common dosage calculations. So, what are some of the routine medication administration schedules, or what are the most common times that we give the medicines? So, a couple of abbreviations that you're going to see routinely throughout your career as a nurse are things like AC. It can be a capital A and a capital C or a lower case a and a lower case c, which means, before meals, Ad lib is as directed.

    00:35 BID is twice a day. PC is after meals. PRN is as needed. QID is four times a day.

    00:43 STAT means immediately. QAM means every morning. Q2H means every two hours. Q4H means every four hours.

    00:55 Couple of medication abbreviation times that you should not use and you should not see is one, QD, which in the old days make Q day, but now, we don't like to use that because it can cause confusion. So instead of writing QD, we will see daily. You want to use that instead of QD. So, what are some words that you have to know when you're giving medications? One is onset. This is the time that it takes a medication after it's given to start taking effect. The peak time of a medication is when the medication reaches its highest concentration in the body.

    01:37 The trough, it is the opposite of the peak. It's the point at which the medication is at its lowest level of effect in the body. You'll want to use trough times four dosing medications such as antibiotics, such as vancomycin. You'll want to trough time to know if you need to change the dose of the medication so that they're getting a steady state of the medication throughout their blood system.

    02:03 Another term you'll see is duration. This is simply how long the medication is going to be effective in the system. So, the duration of a medication may be as short as 30 seconds such as adenosine, or as long as 24 hours such as some chemotherapy.

    02:23 And finally, plateau. This is when the serum concentration of a medication has reached its highest and maintains that same level. So, you'll see plateaus used for things like dosing of warfarin, also known as Coumadin. So you have to have about three doses of Coumadin in your system before you can get a steady state or plateau in your system. So, how do we give medication? Couple of you're probably already familiar with, oral by mouth, pills that you can swallow, pills that you can put under your tongue which is called sublingual, or buccal, that's the inside of the cheek area, or parenteral, that includes subcutaneous which is in the layer of skin, intramuscular which is in the muscle, intravenous or epidural. There's also some topical medications. These go directly on the skin. The most common one you'll probably see are things like topical steroids for rashes or nitroglycerin patches for people with angina. You can also give medications by inhalation. You usually see this with people with respiratory issues such as people with asthma or COPD, when they're asked to inhale a bronchodilator so that it helps get their lungs open. And finally, mucous membranes, this includes, eye such as eye drops, ear such as ear drops, nose such as afrin or something else that you squirt in your nose. It also includes the vaginal suppositories, rectal suppositories, or for some people who can't take anything by mouth and they have an ostomy, you can also give medications through their ostomy side.

    04:05 So, as with everything, there's good and bad. What are the pros and cons of certain rounds of medication administration? So the oral route, well, it's easy, it's convenient. However, might be difficult for some people to swallow these pills or liquids, they might taste terrible.

    04:24 and if your patient has nausea and vomiting or something else going on with their GI tract, they're not going to absorb it very well.

    04:29 Parenteral route is a good route. That's the IV route, the subcutaneous route, the IM route.

    04:37 These are also easy, convenient. However, you're risking infection because you're breaking the skin. Can be painful for some patients. Some people are just scared, absolutely petrified of getting stuck with the needle, and in that case, the parenteral route probably isn't a good choice for them. Topical routes are also painless. They're pretty easy to do, and less side effects. However, if the skin is broken or thin, you might get a different expectation of absorption.

    05:13 In other words, the lotion might go all up and down the arm if the skin is ripped in and transports the lotion that way. Or if there is an area of broken skin, the lotion might burn, or the cream or whatever you're putting on. You might burn the patient.

    05:28 The mucosal route is nice because it's readily absorbable. However, it can cause some local irritation. So, it can cause the mucosal site to get red or a little raw on the patient and they might not prefer that. Or if it's rectal or vaginal, it might not be easy for the patient to give for themselves. The inhalation route is really good for patients, like I said, with respiratory problems, with breathing problems, because that way, they can breathe in the medicine, the medicine goes in pretty quickly and it starts to affect them pretty quickly. However, because you're inhaling it, it might cause systemic side effects. For example, a lot of the bronchodilators can cause your heart rate to increase, which kind of makes people a little nervous and jittery for about the first ten minutes after they take this medication. Some patients don't like that and it's very uncomfortable for them. So, how do we measure our medicine? How do we measure what we're giving the patient? Well, the most common, most accurate system is the metric system. This is most widely used and this is pretty common in hospitals, doctors offices, clinics everywhere you go.

    06:37 So there's things like grams, liters, milliliters, milligrams, and these are all very specific measurements. Old system measurement is called the apothecary system. These were things like a dram which I still don't know what that means because I've never seen it used. But it's a very old system. It was not standardized. We don't use it to measure out medications today. However, we do still slip in household measurements. You will see some medications written as, give one teaspoon or give one tablespoon or drink the entire gallon. We will mix this with the metric system. So it does get a little confusing at times but just kind of keep in the back of your mind that one teaspoon equals five milliliters, a tablespoon equals 15 milliliters, and so on. You just kind of have to remember that. So speaking of conversions, here are some of the common conversions. As I said, a tablespoon is 15 milliliters. A kilogram equals 2.2 pounds. Some medications are going to be based on X amount of drug per kilogram. They don't say X amount of drug per pounds. So you have to know how to convert pounds and kilograms.So, a thousand milligrams is a gram, 500 milligrams is 0.5 grams, a thousand milliliters is a liter, and so on. So the most common formula that you're going to use to figure out drug calculation is called ratio and proportion. It's kind of a reminder back to high school math. So for example, on the screen we have 5:10 = 1:2. So that's saying five is to ten as one is to two. If you remember, the first and last numbers of that equation are called the extremes.

    08:35 The middle numbers are called the mean. So you multiply the means times the extremes to come up with your answer. So for example, 250 milligrams of the drug is in 5 ml of a solution. You need to give the patient 100 milligrams. So, how many mls do we need to give? So we know that there's 250 milligrams in 5 ml.

    09:01 We need to give 100 milligrams is to X ml. We don't know what the X is. So we multiply our means by our extremes, and we get 250x = 100 x 5.

    09:16 Do the math. Xs are being 2 mls of the drug. So if you just kind of think about that, you know that the 2 ml is less than 5 ml and there's 250 milligrams in 5 ml and you need to give less than that.

    09:31 So 2 is the right answer and you've just done a kind of a little immediate self-check in your brain. So, what are the rights of medication administration? Anytime you give a patient a medication, any and every single time you give a patient a medication, you need to ask yourself these five rights. Do I have the right medicine? Do I have the right dose? Do I have the right patient? And do I have the right route? And am I giving it at the right time? Every single time you give the patient a medicine, you should go through these five rights. If one of these is incorrect and you still give the medication, it's considered a medication error. Every single time you give a medicine, ask these little five rights in your head every single time. So, what are the elements of a medication order? A medication order has to be very specific in order for you to give it as the nurse.

    10:30 One, it has to have the patient's name. Two, it has to have the patient date and time that the order is written. It has to have the name of the medication on it, has to have the dose. If it doesn't have all those, you can't take it as a medication order.

    10:46 You have to have the route of the administration, the time and frequency that you're going to give it, and the signature of the prescriber. So for example, Joe Smith takes one 350 milligram Tylenol tablet every six hours as needed by mouth, signed by Jane Doe. If it doesn't have all of those elements, it's not a complete medication order and you can't give it. You can't just make up one of the elements and think you can give the medication. You need to contact the prescriber and say, how often do you want the patient to have this? How did you want the patient to get this? Did you want them to take it by mouth or as a suppository? All of these elements have to be there. You as a nurse cannot make these decisions independently. Thank you. This has been Jill Beavers-Kirby discussing dosage calculations.

    About the Lecture

    The lecture Dosage Calculation by Jill Beavers-Kirby is from the course Physiological Integrity. It contains the following chapters:

    • Dosage Calculations
    • Routes of Medication Administration
    • Medication Measurement Systems
    • 5 Rights of Medication Administration

    Included Quiz Questions

    1. QD
    2. QID
    3. prn
    4. ac
    1. Metric
    2. Household
    3. Apothecary

    Author of lecture Dosage Calculation

     Jill Beavers-Kirby

    Jill Beavers-Kirby

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