Dosage calculation Help!

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Hi! Im in my 3rd semester of my ADN program and we just started advanced dosage calculations and i came across some problems that i have no idea how to do. Here it is:

Drug A 10mg ordered. The pharmacy sends up drug A 5mg/2mL. The drug reference states to dilute to a concentration of 1mg/mL and administer at a rate of 5mg per minute.

  • The total volume the nurse will administer is______mL
  • The nurse will add____mL of dilutent to make the appropriate concentration of the drug.
  • Over how many minutes will the medication be administered over?

Specializes in OR, Nursing Professional Development.
How about this one:

Order: Nitroglycerin 5mcg/min

On Hand: 50mg of nitroglycerine in 250mL of DSW.

Pump Info: Pump will infuse at a tenth of a mL.

Calculate the pump setting or flow rate (per hour)

Well i know that 5 mcg is 0.005 mg so i divide that by 50 mg and multiply by 250 mL and i get 0.025. I know 1 tenth of a mL is 0.1 mL and then im not sure what to do after that.

You need to find out how many mcg are in each mL to see how many mLs you will infuse per minute.

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Second step is to determine how many mLs will give you your 5mcg dose. Now, remember that's per minute, and you need to set a pump to run in mL/hour.

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By "pump will infuse at a tenth of a mL", I believe that is informing you that the pump can run a rate of x.x, not that for this infusion you will run 0.1mL/hour.

The key thing that should tell you you've got your calculations completed correctly is that the units should make sense. If you're setting a pump to run, you need to end with mL/hour. If you're preparing an injection, you should end with a volume that is safe to inject. And so on.

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You need to find out how many mcg are in each mL to see how many mLs you will infuse per minute.

attachment.php?attachmentid=23874&stc=1

Second step is to determine how many mLs will give you your 5mcg dose. Now, remember that's per minute, and you need to set a pump to run in mL/hour.

attachment.php?attachmentid=23875&stc=1

By "pump will infuse at a tenth of a mL", I believe that is informing you that the pump can run a rate of x.x, not that for this infusion you will run 0.1mL/hour.

The key thing that should tell you you've got your calculations completed correctly is that the units should make sense. If you're setting a pump to run, you need to end with mL/hour. If you're preparing an injection, you should end with a volume that is safe to inject. And so on.

I think i have gotten confused already. Was what i did up until this point right or?

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Specializes in OR, Nursing Professional Development.
I think i have gotten confused already. Was what i did up until this point right or?

You do have how many mLs you need to run 5mcg/min (step 1- you did this part). Your pump runs at mLs per hour, so you now need to calculate that step (step 2- you didn't do this part).

ETA: I may have been confusing because there's actually 3 steps: what you have available in mcg/mL, then how many mLs to give you your dose in minutes, and then the conversion to mL/hr. You've done step 1 and then the dose in mL/min, you still need to do the conversion to mL/hr.

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You do have how many mLs you need to run 5mcg/min (step 1- you did this part). Your pump runs at mLs per hour, so you now need to calculate that step (step 2- you didn't do this part).

ETA: I may have been confusing because there's actually 3 steps: what you have available in mcg/mL, then how many mLs to give you your dose in minutes, and then the conversion to mL/hr. You've done step 1 and then the dose in mL/min, you still need to do the conversion to mL/hr.

tt

Ok so would you multiply 0.025 ml by 60? to get 1.5?

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Specializes in OR, Nursing Professional Development.
tt

Ok so would you multiply 0.025 ml by 60? to get 1.5?

Yes. It really helps to set it up on paper the way I have it shown, especially when you're new to dosage calculations or struggling, just because then you can see how the units cancel each other out. Sometimes just using numbers without units and not writing it out can get confusing.

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How about this one:

Order: Nitroglycerin 5mcg/min

On Hand: 50mg of nitroglycerine in 250mL of DSW.

Pump Info: Pump will infuse at a tenth of a mL.

Calculate the pump setting or flow rate (per hour)

Well i know that 5 mcg is 0.005 mg so i divide that by 50 mg and multiply by 250 mL and i get 0.025. I know 1 tenth of a mL is 0.1 mL and then im not sure what to do after that.

** disclaimer...I'm only a pre-nursing student, but I'm trying to learn as much as I can before I start. Hence - this answer could be completely wrong!**

I figured out everything the same as you. Then I think it is this:

* You need 0.005mcg/minute, which is delivered per. 0.025ml of DSW

* This equates to 0.3mcg/hour, meaning a person will need to receive 1.5ml of the DSW solution over the course of an hour

* The amount of solution required over the hour is 1.5ml

* I have no clue about setting pump rates - haven't done that yet, sorry

P.S.. PLEASE CORRECT ME IF I AM WRONG - WANT TO LEARN!! :cat:

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** disclaimer...I'm only a pre-nursing student, but I'm trying to learn as much as I can before I start. Hence - this answer could be completely wrong!**

I figured out everything the same as you. Then I think it is this:

* You need 0.005mcg/minute, which is delivered per. 0.025ml of DSW

* This equates to 0.3mcg/hour, meaning a person will need to receive 1.5ml of the DSW solution over the course of an hour

* The amount of solution required over the hour is 1.5ml

* I have no clue about setting pump rates - haven't done that yet, sorry

P.S.. PLEASE CORRECT ME IF I AM WRONG - WANT TO LEARN!! :cat:

This is right and done well. Good job.

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I think i just psych myself out guys. I failed pharm the first semester and had to take it during the summer. I learned a lot that summer and passed with a B but I have always had this fear of math and since i failed pharm, i have had a fear of failing again because of math and then they say "Advanced calculations" and it just freaks you out, ya know? but im not going to let that happen again.

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This is right and done well. Good job.

That's good to hear! I second guessed myself because I was thinking, "how on earth can you deliver such a microscopic amount and be accurate??" so I searched for info about the pumps, and realized there are machines that can handle extremely small dosages...well, DOH! Proves how much I have to learn! :roflmao:

I thought this was all to do with an IV delivery, didn't even realize there were such things as pump infuser machines! Anyway - happy to hear my calculations were correct. Thanks for letting me know!

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** disclaimer...I'm only a pre-nursing student, but I'm trying to learn as much as I can before I start. Hence - this answer could be completely wrong!**

I figured out everything the same as you. Then I think it is this:

* You need 0.005mcg/minute, which is delivered per. 0.025ml of DSW

* This equates to 0.3mcg/hour, meaning a person will need to receive 1.5ml of the DSW solution over the course of an hour

* The amount of solution required over the hour is 1.5ml

* I have no clue about setting pump rates - haven't done that yet, sorry

P.S.. PLEASE CORRECT ME IF I AM WRONG - WANT TO LEARN!! :cat:

Hi there, I think you may have switched your .005 mg with mcg. .005mcg is = to 5 nanograms, we dont give nanograms of medication.

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Hi there, I think you may have switched your .005 mg with mcg. .005mcg is = to 5 nanograms, we dont give nanograms of medication.

Actually, not true. Flolan is dosed ng/kg/min.

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Well there you go!

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