Nursing Students General Students
Published Jun 2, 2005
S.N. Visit, BSN, RN
1,233 Posts
How can I make this problem into a simple equation? ( I've figured the answer by doing the drawn out process of making a chart, but that takes too long.. Is there a simplilar way?)
My example question is: A patient takes 50mg of a drug that has a half life of 12 hours. What percent of the dose remains in the body 36 hours after the drug is administered?
Please remind me how to figure percents????
Thanks in advance to all you smarty pants
mariedoreen
819 Posts
How can I make this problem into a simple equation? ( I've figured the answer by doing the drawn out process of making a chart, but that takes too long.. Is there a simplilar way?)My example question is: A patient takes 50mg of a drug that has a half life of 12 hours. What percent of the dose remains in the body 36 hours after the drug is administered?Please remind me how to figure percents????Thanks in advance to all you smarty pants
You're starting with 50 mg.
12 hours later you will have 25 mg.
12 hours later (24 from the beginning) you will have 12.5 mg.
12 hours later (36 from the beginning) you will have 6.25 mg.
6.25 divided by 50 = .125 or 12.5% remaining.
You're starting with 50 mg.12 hours later you will have 25 mg.12 hours later (24 from the beginning) you will have 12.5 mg.12 hours later (36 from the beginning) you will have 6.25 mg.6.25 divided by 50 = .125 or 12.5% remaining.
Thanks for answering Mariedoreen, :)
That's exactly how I did the problem and came to my answer too. I'm wondering is that they only way to figure the problem?
colleennurse, ASN, RN
342 Posts
I was just reading through this and I am confused as to why you would not stop at 6.25? Why would you divide out again?
lady_jezebel
548 Posts
she's not. this was to calculate %. she needed to find out what percentage 6.25 is of the original dose (50).
Just bumping the thread in hopes of more replies :)
pricklypear
1,060 Posts
OK, my pea sized brain is smoking now, but I think I figured out a formula for you!! I tried it out twice and got the right answer, but don't know if it's always gonna be right!!
X(.5 to the h power) = residual (I hope you know what I mean by power? Squared, cubed, etc? I don't know how to do it on the computer!)
X = starting amount of drug
.5 = half life constant
h power = number of half-life cycles (divide total hours by half-life of drug)
So - 36 hours / 12 (half life) = 3 half life cycles
50mg(.5 to the 3rd power) = 6.25mg residual after 36 hours
(.5x.5x.5)
Percent is part/whole x 100
so - 6.25/50 = .125
.125 x 100 = 12.5%