Drug administration questions

SeekingRem

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Hi there. So I have been studying in advance for my Medic program and I have a few questions regarding giving medications. I hope this isn't as jumbled up as I think it is, and I hope you can make sense of my rambling.

From what I've gathered, there's essentially 3 formulas I need to know.

Volume on Hand x Desired Dose / Concentration.

From what I understand, this formula is used to draw medications up from a vial, and the concentration is the total amount of the drug within the vial, and the volume is the amount of fluid in the vial. For example, if I had a vial that was 10ml and contained 20mg of a drug, and I wanted to draw up 6mg of a drug, my formula would be 10ml x 6mg / 20mg = 3ml. So in order to get my desired dose of 6mg, I would need to draw up 3ml. Right?

The next formula I found was for a drip? I think.
Volume on Hand x Desired Dose x Drip Factor / Concentration?

This one really kind of confuses me, and I guess this is a multi-facet question. I've read up on some drugs and protocols and I'll use an example I've found in Amiodarone. The first dose in V-Tach, V-Fib it says that you give 300mg IV which I assume I would use the first formula for this case. I would draw the 300mg from the vial and then just push it into the IV. But then, it's second dose is 150mg/10 minutes. After digging further, I see that people are inserting the medication into saline bags and then setting them as a drip. Is this common with a lot of other drugs? Is this what that formula above is for? Would it be something like this?

100ml (saline bag) x 150mg (desired amiodarone dose) x Drip factor? (I can't find much when I try to look up drip factor. I'm unsure what that is exactly, if you could help me that would be great) / 150mg (dose of amiodarone)

The last formula I found was..
Volume to be Infused x Drip Factor? / Time.

I'm pretty confused on the last two formulas and how/when I'd implement them in the field. If anyone could help me out that would be great. I'm currently trying to study my protocols ahead of time so I have an early start.
 

cprted

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300mg is in cardiac arrest and given as an IV push. Concentrations will vary, but at work, we carry it in vials of 50mg/ml. Thus to draw up 300mg, I need 6ml from the vial.

150mg in 10 minutes is used in a perfusing VTach. From the same vial were need 3ml (3x50=150). Once that is drawn up it gets injected into our 50ml bag of fluid (we normally use a 50ml bag, could use any other size you want). To calculate a drip rate, volume to be infused multiplied by the gtts/ml of the admin set (standard is 10), divided by the time in which we want to give it.

In this case, our volume to be infused is 50ml (ok, 53ml, but lets keep the math straightforward). Your 150mg dose of amiodarone is contained within the 50ml of the fluid. Multiplied by 10 (the size of the drops in your admin set). So by multiplying 50x10, we know that we need 500 drops through the admin set to give our dose of drug. Divide 500 by the time in minutes, in this case 10, gives us 50 drops per minute.
 
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cprted

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Lets do another one. We want to give a pt with an asthma exacerbation an infusion of Magnesium Sulfate. Under my guidelines at work, this pt can get 2g infused over 20 minutes. We carry MgSO4 in a concentration of 500mg/ml. To draw up 2g, I will need to draw 4ml from the vial. 4x500mg=2000mg=2g. This gets added to a 250ml bag of saline. So our 2g dose of MgSO4 is contained in the 250ml (yes, 254ml) of saline.

So, our volume to be infused is 250ml. Multiplied by 10 (standard drip set). 2500gtts, divided by 20 minutes. 125gtts (drops) per minute or 2 gtts (drops) per second.

Or we could use a 50ml bag again. 2g into a 50ml bag, the volume to be infused is 50ml. Multiplied by 10. 500 gtts. Divide that by 20 mins, 25gtts (drops) per minute or 1 drop every 2 seconds.

I sincerely hope this is helping and not muddying the waters more.
 

Akulahawk

EMT-P/ED RN
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As Gurby says, you really need to understand the basics of how these formulas work. The easiest way to do that is to take a basic course in algebra. The other way to do that is to follow the link that has been provided as that particular site has a ton of information about a lot of different subjects. I generally prefer to have someone actually teach me in class because it allows for a more direct communication between teacher and student so that if there any questions, they can be immediately answered.
 
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SeekingRem

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Do yourself a favor and forget that formulas exist for this stuff, at least for now. Start at square 1 by learning the basic algebra that makes those formulas work, and you will be able to answer your own questions. If you work through all of the videos and exercises in this section, you will be a pro:
Thanks for the reply! I'll definitely check those out, but I'm actually really good at Math. I've taken up to Calculus 2 in Uni, I more so was just confused as to "drip sets" as I still am a little foggy on what those are, and why/when we choose to mix a drug into a bag of saline, lactated ringers, or d5w? The math for me is fairly easy, I'm more trying to figure out what to put where in regards to drugs doses, fluids and what sizes of bags to use, and why you choose to mix in the fluids you choose.
 

Gurby

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Thanks for the reply! I'll definitely check those out, but I'm actually really good at Math. I've taken up to Calculus 2 in Uni, I more so was just confused as to "drip sets" as I still am a little foggy on what those are, and why/when we choose to mix a drug into a bag of saline, lactated ringers, or d5w? The math for me is fairly easy, I'm more trying to figure out what to put where in regards to drugs doses, fluids and what sizes of bags to use, and why you choose to mix in the fluids you choose.
Drip sets regulate how fast the fluid comes out of the bag. The unit "gtts" represents how many drops per mL - I think this is what people mean when they say "drip factor". So a micro drip set may have 60gtts, which means it takes 60 drops per 1mL. When you're adjusting the rate, you count drops to judge how fast the fluid is coming out: 1 drop every 1 second = around 60 drops/min = 1mL/min.

If you wanted to infuse a bunch of saline all at once, you'd probaly use a macro drip set (usually 10gtts or 15gtts). If setting up a med infusion you're more likely to mix some amount of drug with a 100mL or 250mL bag of saline and then use a micro drip set.
 

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