# Need simpilar way to figure equations.

Posted

Specializes in Home Health Care. Has 8 years experience.

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

Specializes in Med-Surg. Has 3 years experience.

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.

Specializes in Home Health Care. Has 8 years experience.

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.

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?

Specializes in post-op. Has 8 years experience.

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?

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?

she's not. this was to calculate %. she needed to find out what percentage 6.25 is of the original dose (50).

Specializes in Home Health Care. Has 8 years experience.

Just bumping the thread in hopes of more replies :)

Specializes in Telemetry, ICU, Resource Pool, Dialysis. Has 11 years experience.

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%

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