Dosage Calculations

[minnielynn]

I am in a desperate situation. I thought I was getting my calculations correctly and today I got back my math results and i got a 70% I am so disappointed I dont know what to do. On my first exam I received an 80%.

My professor said that if i get above 95% on my final (which is next week) I may be able to average a b+ or a- , but it will all depend on the overall average, if he curves grades or not. I went and bought 2 self help books on calculations .... My question is ..... do you think it is humanly possible to ingest all this info by next week (exactly a week from today)! I am having problems with the drips and the three step conversions. Is there a website that can help me? To top it off my professor sucks, so what I have learned, I have learned on my own. I am so frustrated, so much so, that it is getting harder and harder for me to pick up a book .....sorry for venting

[tabymac]

My school advised us to purchase and study a dosage & calculations book and we take a test (50 ?'s) before each semester.

We do not get any instruction (they don't have a class to teach you the math) but the week before the exam they have a question & answer session to assist us with any burning questions before the exam.

They post the specific chapters we should study at the end of the previous semester - so you have ample time to prepare. I have found that this book is easy to understand - takes you back to the basics (so you can jump to the level you're most comfortable with) and they also cover several (2-3) different methods of solving problems - since math can be taught/learned different ways.

The book also teaches you short cuts, which I found very useful for testing purposes (some students fail the test because they don't finish...) check it out:

I have the 3rd edition: Calculate with Confidence by Morris, D.G. (2002) St. Louis: Elsevier ISBN: 0-323-01349X

the newest version: (2006) ISBN: 0-323-029280

Hope that helps

[Lesli61]

I got a workbook called 'Dosage Calculations' 7th Edition by Gloria Pickar. You can buy it at BarnesandNoble or Amazon.com It is a really great book. It shows you several different calculation methods, with lots of practice problems. The later chapters cover the more advanced topics, like titrating IV's and BSAs. There are comprehensive exams at the back so that you can test yourself. There are lots of diagrams and photos, and throughout the book they use sample MAR sheets and order sheets with hypothetical clinical situations and related questions.

My school offers majors in nursing, radiology, surg tech, etc. so everyone must take a basic 'applied math' class that covers dosage calcs along with basic algebra, geometry, and trig. I took the class by exam, after studying the book mentioned above, and passed with flying colors! :chuckle I think Pickar's book may also come in handy as a reference later on.

Good Luck!

[Carla25]

My school taught us dimensional analysis, but if you know ratio proportion it was okay too. I would just start studying your values first then try your math.

Example: 15 grains = 1 Gram; 1 gram = 1000 milligrams

I attached some conversions that helped me in pharmocology

conversions.doc

[emtb2rn, BSN, RN, EMT-B]

tookewlandy said:

Ok i went out and bought htis Dimensional analysis for meds book and as i posted this has helped me lots, But the school wants us to buy a book called CALCULATE WITH CONFIDENCE. It says i teaches DA and ratio and proportion, and FORMULA(what is formula).

Yeah, my school wants me to get Calulate with Confidence too. I already picked up Pickar's Dosage Calculations based comments here, so I'm gonna just use that for now. We'll see what happens...

[emtb2rn, BSN, RN, EMT-B]

Here's a really good Dimensional Analysis website: http://www.alysion.org/dimensional/analysis.htm

[puggymae]

I teach dosage calculations - the reason many students are unsuccessful in my class is one of two things: 1 - they cannot do simple elementary school math calculations. You don't have to be able to do calculus - just add, subtract, multiply, and divide whole numbers, fractions, and decimals. 2- the student never learned their conversion factors (1 kg = 2.2 lbs for example) and abbreviations. If you do not understand something in class tell the teacher right then. Other people probably don't get it either, and if you don't tell the instructor you don't get it, the instructor assumes that you do. Sooo.. brush up on your math skills, make sure you know your abbreviations and conversions, and tell your instructor if you don't grasp a certain concept. Good luck!

[poor25]

Does anyone know a good/quick way to learn the equivalent units for converting from household to apothecary or metric. I am working on dosage calculations and the math practicum is on Saturday and I am still struggling to remember anything.

[Daytonite, BSN, RN]

I would recommend that you do the same sort of thing our trigonometry instructor had us do to help us learn the measurements of the sides of right triangles and their trig functions. Make a table and memorize how to recreate it. As soon as you get the test, the first thing you do is draw that table from memory before you even attempt to do any of the problems on the test. So, look at the conversions you want to put on a table. Do you see any kind of pattern in the numbers (like a sequence) that might make it easier for you to remember when writing them down? Create this table of conversions for yourself. Then, copy it. Over and over. Every time of every day that you think about it. Do it so it only takes you a couple of minutes to draw and fill in the numbers on this table. Start now. By Saturday you should be able to copy this table onto to your test paper where it will be in black and white for you to refer to when you are under the pressure of having to perform the math on a test. This works. I guarantee it.

Welcome to allnurses!

[Race Mom, ASN, RN]

30 monkeys Laughed at 1 old zebra

8 dozen roses, 2 Turkeys, 6 tums.

30 mL's = 1 oz. = 8 dr (drams) = 2 Tbs = 6 tsp

That's one that always sticks with me! They're all equivalent. So if you had that memorized and you had to answer how many ml's in 4 drams, just divide all numbers by 2. 4dr, 15ml, 1Tbs, 3 tsp.

As far as the metric, just memorizing the top middle and bottom figures, the rest can be figured out by simple math. Like memorize what 1gm equals, what 100mg equals, what 60mg equals, what 1mg equals. If you know what 1gm is (1000mg), then you can figure out what 500mg's equals without having to "memorize" it.

Good luck!

[Megsd, BSN, RN]

One trick I learned to convert grains to milligrams is to think of a clock face (which is much easier if you can draw it, but bear with me).

At the top is 60 minutes (1 hr), on the right is 15 minutes, at the bottom is 30 minutes, and on the left is 45 minutes. 15 minutes is 1/4 hour, 30 minutes is 1/2 hour, 45 minutes is 3/4 hour, and 60 minutes is 1 hour.

1 grain = 60 mg, so

1/4 grain = 15 mg,

1/2 grain = 30 mg

3/4 grain = 45 mg

Thanks for the mnemonic for drams, tsps, etc. I avoided studying drams like the plague and luckily they weren't on THIS dosage test, but I'm sure it'll come up!

[Daytonite, BSN, RN]

emsjunkie2001 said:

pronestyl 4 g in 1000 ml d5w, infuse at 2 1/2 mg/ min..

i know the answer is 38 ml/hr. but can't figure out how to get this.

I am going to work this out by dimensional analysis for you, but let me also explain how i got the equation i am going to use for the dimensional analysis, or factor label method.

If you use the formula dose desired divided by dose on hand you will come up with the following complex fraction (a fraction in the numerator and a fraction in a denominator): 2.5 mg / 1 minute divided by 4 grams / 1000 ml. Remember that when you divide with a fraction that is in the denominator, you must multiple both the numerator and denominator by it's reciprocal fraction in order to clear the denominator of the fraction. That is going to leave you with the equation for the dimensional analysis that i am presented below. This is why 4 grams / 1000 mg now becomes 1000 mg / 4 grams in the equation below.

The object of using dimensional analysis is to manipulate the labels on all the terms in your equation and factor them out so all you are left with are the labels you want left on the final answer. In this case, the labels you want to be left with are: ml / hour.

2.5 mg / 1 minute (dose desired)

x 1000 ml / 4 grams (dose on hand)

x 1 gram / 1000 mg (conversion factor)

x 60 minutes / 1 hour (conversion factor)

= 37.5 ml / hour (after duplicate labels are cancelled out)

= 38 ml / hour

(final answer rounded up)

[LadyT618, MSN, APRN, NP]

trilli18 said:

ok very frustrated thought I was getting this dosage calculation stuff and Im not. My professor suggested doing it as desired over have. I tried but am still coming up with wrong answer. Can some please help me

Here's the problem need to find desired dose:

ordered 1 1/2 teaspoon Zithromax 200mg/5ml PoQ6h

on hand 200mg per 5ml

If u could show me how to do this problem by solving it as desired over have I would appreciate it ---Thanks for ur help

Bear with me, I'm not good at setting problems up, but let me tell you how I would walk thru it. First I would figure how much of this drug is in 1ml. If you do the math, 200/5= 40mg/ml. Don't read too much into the question. Sometimes they give u more info than is needed. They already told u the concentration of the drug. They actually gave u the desired amount, u just have to convert that to a dose. All u have to know is conversion factors. 1tsp=5ml. So, 1.5 x 5ml = 7.5ml. So 7.5ml x 40mg = 300mg. There is your dose.

Remember, not all problems require desired over have. Hope I did not confuse u too much.