# Need Help with Drug Calculations

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So, I'm in paramedic school and we are currently working on drug calculations. And it's all greek to me. The way its been described to me is thusly:

There are three basic calculations that need to be mastered: weight-based, non-weight-based, and fluid to be administered over time.

ordered dose x patients weight in Kg x drip set(gtt/min)

---------------------------------------------------------------------------------- = Weight-based

concentration

ordered dose x drip set(gtt/min)

------------------------------------------------ = non-weight-based

concentration

volume to be administered x drip set(gtt/min)

--------------------------------------------------------------- = fluid to be administered

time in minutes

We've gone over all of these in class multiple times and I can usually have a pretty good grip on it by the end of class. But as soon as I leave school and go home to do some practice problems, I'm drawing a complete blank. It is just not clicking for me. I've got all of the formulas written down and have them in front of me, but when I look at them, I feel like I'm looking at hieroglyphics. Any tricks or suggestions on how to make this sink in? Thanks.

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With algebra not being a strong point, I had a little trouble at first too. What I did is simple repetition. I took 2 of every homework assignment, then looked up some more on the internet. Practice practice practice...the more the merrier. Then make up some problems and try to do them in your head, it'll help it sink in.

Also, the first 2 equations have one thing in common.. The only thing on the bottom is the concentration (dose on hand). All other variables go on top.

Try to keep it simple, eliminate any other numbers they throw in a question to mess you up, and stick with the equations. Plug in your variables, and you're golden.

These are the formats I used. Dd= Desired dose, Dh= Dose on hand (the vial/amp etc)

Dd/kg/gtts

----------

Dh

Dd/gtts

-------

Dh

Whatever number you end up with is the gtts/min.

Edited by EMT Foose
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Honestly bro, I preferred to learn one formula, it as as follows...

Weight x dose x volume x drip set

Concentration x time

Basically, you take what you need from the formula to get your answer. If your equation does not need a drip set, then just remove it from the formula.

For example, try a Lidocaine Bolus.

Weight of the patient is 100 kg

Dose to use is 1.5 mg/kg

Concentration of the drug is going to be 20mg/cc

So, to set up our formula...

Weight (100 kg) x Dose (1.5 mg/kg) x Volume (1 mL)

-----------------------------------------------------------------------------

Concentration (20 mg)

150 mL

------

20

= 7.5 mL of Lidocaine to be administered

Notice that in the equation we did not use Time or Drip Set because this is not a drip. To complete the equation multiply everything on the top. Then multiply everything on the bottom. Divide the two numbers. Also, remember that you have to cancel out the units. The kg and mg cancel out, and that leaves you with mL.

Next we can try a drip. Again, we will use the basic formula and just plug in the numbers.

Weight of the patient is 100 kg

Dose to be give is 5 mcg/kg

Volume of the drug is 500 mL

Concentration of the drug is 800 mg

Time in which it is to be give is 1 min

Plug the numbers into the basic formula. Multiply, divide, then you will have the answer.

Weight (100 kg) x Dose (5 mcg/kg) x Volume (500 mL) x Drip Set (60 gtt/min)

---------------------------------------------------------------------------------------------------------------

Concentration (800 mg) x Time (1 min)

For any formula the units need to be the same. In the previous equation there are mcg and mg. We will change mg to mcg. Thus...

Weight (100 kg) x Dose (5 mcg/kg) x Volume (500 mL) x Drip Set (60 gtt/mL)

---------------------------------------------------------------------------------------------------------------

Concentration (800,000 mcg) x Time (1 min)

15,000,000 gtt

----------------------

800,000 min

= 18.75 gtt/min

Remember, kg, mcg, and mL all cancel out. Thus leaves you with gtt/min (gtt=drops)

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Mateo, I haven't had time to do any practice problems with the formulas you provided, but thanks for the help. I'll let you know how it goes.

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Mateo, I haven't had time to do any practice problems with the formulas you provided, but thanks for the help. I'll let you know how it goes.

The beauty of my previous post is there is only one formula. Take the values that you need and plug 'em in. Practice will certainly make you better. Good luck with it man! If you are dedicated, then you will soon understand it. Just ask if you have any more questions.

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Personally I've never been one to use formulae for med calculations. I've always relied on my algebra skills instead.

For Example. Billy-Bob requires medication X. The weight based dose is 1mg/Kg/hour. The patient weighs 70Kg and medication X comes in a concentration of 0.7mg/mL. What drip rate should you set your pump at in gtts/min using a 10gtt/mL dripset.

If you break it into parts things are much simpler.

1) (1mg/Kg/hour)*(70Kg) = 70mg/hour (for Billy-Bob with a weight of 70Kg)

2) (70mg/hour)*(1mL/0.7mg) = 100mL/hour (of this 0.7mg/mL concentration medication)

3) (100mL/hour)*(10gtt/mL)*(1hour/60min) = 16.7gtt/min

If for example you are making up your own minibags for medication admin it can be worked out based on other information given but I'll leave that for another post if you find my methods effective for you. In the end go with whatever works for you personally. Sometimes half the battle is finding a method that works for you.

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• 1 year later...

Honestly bro, I preferred to learn one formula, it as as follows...

Weight x dose x volume x drip set

Concentration x time

Basically, you take what you need from the formula to get your answer. If your equation does not need a drip set, then just remove it from the formula.

For example, try a Lidocaine Bolus.

Weight of the patient is 100 kg

Dose to use is 1.5 mg/kg

Concentration of the drug is going to be 20mg/cc

So, to set up our formula...

Weight (100 kg) x Dose (1.5 mg/kg) x Volume (1 mL)

-----------------------------------------------------------------------------

Concentration (20 mg)

150 mL

------

20

= 7.5 mL of Lidocaine to be administered

Notice that in the equation we did not use Time or Drip Set because this is not a drip. To complete the equation multiply everything on the top. Then multiply everything on the bottom. Divide the two numbers. Also, remember that you have to cancel out the units. The kg and mg cancel out, and that leaves you with mL.

Next we can try a drip. Again, we will use the basic formula and just plug in the numbers.

Weight of the patient is 100 kg

Dose to be give is 5 mcg/kg

Volume of the drug is 500 mL

Concentration of the drug is 800 mg

Time in which it is to be give is 1 min

Plug the numbers into the basic formula. Multiply, divide, then you will have the answer.

Weight (100 kg) x Dose (5 mcg/kg) x Volume (500 mL) x Drip Set (60 gtt/min)

---------------------------------------------------------------------------------------------------------------

Concentration (800 mg) x Time (1 min)

For any formula the units need to be the same. In the previous equation there are mcg and mg. We will change mg to mcg. Thus...

Weight (100 kg) x Dose (5 mcg/kg) x Volume (500 mL) x Drip Set (60 gtt/mL)

---------------------------------------------------------------------------------------------------------------

Concentration (800,000 mcg) x Time (1 min)

15,000,000 gtt

----------------------

800,000 min

= 18.75 gtt/min

Remember, kg, mcg, and mL all cancel out. Thus leaves you with gtt/min (gtt=drops)

I sent you a PM, Mateo.