# Pharm

Published

Hello

does anyone have any real good websites that assist with dosage calculations? My book, Calculate with Confidence has a cd but I don't care for it as it has a distinct bias in favor of ration proportion and I use the d/h xQ thing.......

Just wigging before mandatory pharm assessment...........

Lynn Fowler

573 Posts

Specializes in CICu, ICU, med-surg.

13 Posts

Originally posted by twarlik

I like this one: http://www.accd.edu/sac/nursing/math/default.html

Thanks so much.....I'm in my first sem ADN and this is a do or die exam to go on to clinicals. We must have a least an 80%, Math is my personal demon.......lol.

Lynn:rolleyes:

50 Posts

Hi Lynn, I have to give credit to an instructor named W A Howland who posted this info on the AOL Nursing Board..great info - so thought I would share.

Good Luck in your program! Will be so glad when I finally reach the point you are at..:)

Lisa

This is gonna give you a method to do med math calcs that wil never fail you. I taught this to arithmetic-challenged students for years, and I use it myself for all sorts of purposes, including recipe scaling .

============================================================

OK, so get out a piece of paper and a pencil, because this doesn't always come out right in email land

Suppose you have, oh, an ampule of Cleocin that is labeled "600mg in 5cc." You have to give a dose of 350mg.

Write the following, because you know this to be true :

600mg = 5cc

Underneath it, so the equal signs are even and the units are the same on each side-- mg on the left, in this case, and cc's on the right. Use a question mark, not some other symbol like an x, because question marks are pretty unthreatening.

350mg = ?cc, because you have this question: 350mg are in how many cc's?

Now, draw an arrow from bottom to top between the only number you have on the bottom (the 350) in an incline to the other side, in this case, to the 5. It might help you to imagine this as part of an "X", meaning "times." SO, multiply those two numbers.

Now draw a little rainbow-shaped arrow across the top to the only other number you have before you, the 600. If it helps, draw little dots just above and below the apex of the rainbow, like the division sign, because you're going to divide by the only number you have left, the 600. Voila. Your answer.

Now, the beauty of this is that you can do it either way-- you can NEVER make a mistake by putting something else first or last. All you need to know is what you have and what you want, and line things up with the same units of measurement on the same sides of the = sign. Don't believe me? Try it.

5cc = 600 mg or 600mg = 5cc

?cc = 350 mg 350mg = ? cc

Arrow from bottom number to opposite top number (multiply), divide by the only number you have left. Bingo.

You can use this for anything. Try this one. You have a liter of fluid to give over 6 hours. How fast do you set the pump (cc's per hour)?

1000cc = 6 hours OR 6hrs = 1000cc

?cc = 1hr 1hr = ?cc

(I hope these lined up. If not, you know how to do it.)

Your chickens lay 38 eggs per month. How many eggs will they lay in three weeks?

38 eggs = 4 weeks or 4 weeks = 38 eggs

?eggs = 3 weeks 3 weeks = ?eggs

Or maybe:

38 eggs = 31 days or 31 days = 38 eggs

?eggs = 21 days 21 days = ?eggs

depending on the amt of precision you need in egg prognostication .

I hope you're seeing a pattern here. To set up any problem, you first write down what you know. This is because it's always important to start anything in life with what you know already . The you write down what you want to know, because it's very important to know where you want to go. Then you multiply from the bottom to the opposite top, and divide by the only number you have left. Done.

If you have a problem with multiple units, you can use the same method, but you do it twice. For example:

Give 0.8 mg/kg/hr of a solution that holds 500 mg/L to a pt that weighs 48 kg.

First you need to know what you know: You're gonna want to give how much?

0.8 mg = 1 kg or 1 kg = 0.8mg

?mg = 48 kg 48 kg = ?mg

because you want to know how many total mg you're gonna need to pump into this particular 48-kg body every hour. Lessee, now, that's 48 x 0.8, divided by one, = 38.4 mg.

But now you need to know how many cc's that is.

OK, so you know that

500 mg = 1000 cc or 1000cc = 500mg

and you want to know how many cc's 38.4 mg would be, so you can set the pump to deliver that much

500mg = 1000 cc or 1000cc = 500 mg

38.4 mg = ?cc ? cc = 38.4 mg

OK, so 38.4 times 1000 divided by 500 is.... um, lessee now, 76.8 cc, or 77 cc in real life. 77 cc/hr will give you that 0.8mg/kg for that patient.

Your new car gets 31 mpg. Gas costs \$1.35 per gallon. Your charge statement indicates you spent \$46.50 on gas going to visit Grandma. How many miles did you drive?

31 miles = \$1.35 (right? because you get 31 miles for a gallon and gas costs \$1.35, so you go 31 miles for every \$1.35 you give to Big Oil)

? miles = \$46.50

So that's 46.50 times 31 (bottom across to top multiplying), divided by 1.35, the only number you have left, equals 1067.7 miles. She must be a really neat Grandma. And gas was cheaper then, too.

I hope this helps. Try a few problems that you have in your med math book with this method, then check the answers in the back and see if you get the same one. Betcha you will.

:) :)

802 Posts

I hope this helps. Try a few problems that you have in your med math book with this method, then check the answers in the back and see if you get the same one. Betcha you will.

:) :)

SWEEEEET!!!!

Thanks:D

13 Posts

Thanks for math help,! I appreciate any words of wisdom with it........

Lynn

1,093 Posts

here are the best words of wisdom i ever learned....learn it all...learn to do it w/o a calculator, and learn how to do it every way possible... because sure as not you will be stuck on the floor w/o any resources figuring out a calc...i can't tell you how many RN's i have worked w/ that can't do a simple calc because they relied on "stuff" during school.l

13 Posts

Originally posted by athomas91

here are the best words of wisdom i ever learned....learn it all...learn to do it w/o a calculator, and learn how to do it every way possible... because sure as not you will be stuck on the floor w/o any resources figuring out a calc...i can't tell you how many RN's i have worked w/ that can't do a simple calc because they relied on "stuff" during school.l

Thanks for those tidbits of wisdom......It will prove to be interesting especially since we've been told, all systems will be fully computerized any day. System is up and running and "supposidly" working out all the bugs.....Nur 3 students are having a bear of a time unlearning and re learning computer stuff.......

By the way, Pharm test was fine.......grades tomorrow, but I passed it, I think........LOL

Lynn:D

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