Drug Calc Help

[mhink3989]

Hello all!
I'm in medic class and having quite some trouble with my drug calcs. I've always, through my years of schooling, had trouble in math and now really need the skills! any suggestions on books? or helpful hints?
thanks!
-Melissa

 

[Veneficus]

If you are at an accredited college there should be a math lab or tutor. There are some websites that may have a few shortcuts for certain medications, but the easiest thing to do is learn a conversion factor.

What medic text are you using, the 5 volume Brady makes it really easy. send a PM if that doesn't help and I will see what else I can do.

 

[SoCal]

PM me if u need help, I can give u some formulas that help.

 

[FL_Medic]

DRUG CALCULATIONS​

The Master Formula:

DD x Wt x SS
C x T​

DD = Desired Dose
Wt = Weight
SS = Solution Set
C = Concentration
T = Time





What is it?
The Master Formula is a formula that can be used for all infusions. It was developed by my paramedic instructor and is currently a standard in many educational facilities.

How do I use it?
You plug the appropriate numbers into the previously defined variables. This means that if you are not administering a weight based medication & dose that you do not need to use that portion of the formula. I will explain in the fallowing.



DD x Wt x SS
C x T

• Let’s try an example with Dopamine:

• Your dose for Dopamine starts at 5mcg/kg/min.

• This tells us that we will be using the weight (wt) portion of the formula.

• First we plug the dose, and weight into the formula. Lets say our patient is 110 lbs. That equals 50 kg, because 1 kg = 2.2 lbs.

5mcg/kg x 50kg x SS
C x min.

• Notice that the time portion of the dose replaces Time (T) on the bottom of the formula.

• Now we still need our solution set (SS) and concentration (C).

• We will be using a 60gtts/ml drip set.

• Dopamine comes packaged 400mg in a 250ml premixed bag.

5mcg/kg x 50kg x 60gtts/ml
400mg/250ml x min.

• Since our dose is in micrograms we need to convert our concentration from milligrams to micrograms.

• 1mg = 1000mcg

5mcg/kg x 50kg x 60gtts/ml
400,000mcg/250ml x min.

• Next we need to get our concentration simplified to per 1ml (1cc). This means that you divide both sides of the concentration by the volume (milliliters).

• 400,000 divide by 250 = 1,600

• 250 divided by 250 = 1, We do not show the numeral 1 when there is a variable fallowing it(1ml = ml).

C= 400,000mcg/250ml = 1,600mcg/ml

• Now we can plug our simplified concentration into the formula.

5mcg/kg x 50kg x 60gtts/ml
1600mcg/ml x min.

• Now it’s time to start simplifying our formula.

• First you can eliminate all variables that you see twice

• Since mcg is on the top and the bottom we cross them out


5mcg/kg x 50kg x 60gtts/ml
1600mcg/ml x min.

• Do the same with kg &ml.

5mcg/kg x 50kg x 60gtts/ml
1600mcg/ml x min.

• Now you can rewrite the formula without the crossed out variables.

• This will show you what form your dose should end up in. In this example gtts/min.

5 x 50 x 60gtts
1600 x min.

• Now you can just do the math.

• The easiest way is to cross out the zeroes. Cross 1 zero off the top and 1 off the bottom. Then do it again. You will be left with 16 on the bottom.


5 x 50 x 60gtts
1600 x min. =

5 x 5 x 6gtts
16 x min.

• Now divide top and bottom by 2


5 x 5 x 3gtts
8 x min.

• This is as far as you can simplify so multiply the top then divide product by the bottom.
1.) 5 x 5 x 3gtts
8 x min.

a.) 5x5 = 25
b.) 25x3=75

2.) 75gtts
8min.

• 75 divided by 8 = 9.375. Round to the nearest whole number.
• > 0.5 round up. < 0.5 round down.

ANSWER: 9gtts/min.

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

Here are some weight conversions to remember:

10kg = 22lbs 60kg = 132lbs 90kg = 198lbs
20kg = 44lbs 65kg = 143lbs 95kg = 209lbs
30kg = 66lbs 70kg = 154lbs 100kg = 220lbs
40kg = 88lbs 75kg = 165lbs 110kg = 242lbs
50kg = 110lbs 80kg = 176lbs 120kg = 264lbs
55kg = 121lbs 85kg = 187lbs 150kg = 330lbs



Concentrations to remember:

NTG (Tridil) = 25mg/250ml = 100mcg/ml
Dopamine = 400mg/250ml = 1,600mcg/ml
Diprivan = 500mg/50ml = 10mg/ml = 10,000mcg/ml
Amiodarone = 150mg/100ml = 1.5mg/ml
Epinephrine (Infusion for anaphylaxis/bradycardia) = 1mg/250ml = 4mcg/ml













Here are some tricks:

Dopamine:
Dose: 5mcg/kg/min
Take the patient’s weight in pounds, drop the last number, and subtract 2. This will give you your drip setting using a 1600mcg/ml conentration, and 60 gtts/ml drip set.
[Weight(lbs), drop last number] – 2 = gtts/min.

ex. 120 lb pt.
1. 120 -- drop the zero
2. 12 -- now subtract 2
3. 10 -- 10 gtts/min.


Amiodarone:
Dose: 150mg/100ml(D5W) over 10min.
Use 10gtts/ml drip set.
The easy way to do this is forget the drug when calculating. Whenever you need to give fluid over a time period just devide the total fluid by the time in min. Then multiply by drip set to get gtts/min.
100(ml) / 10(min) x 10(gtts/ml) = 100 gtts/min
About 3 gtts/2 sec


Mag Sulfate:
Dose: 1g/100ml(D5W) over 10-20min
A Magnesium sulfate dip is similar to an Amiodarone drip because its the same total amount of fluid.
100 gtts/min for 10min. dose
50 gtts/min for 20min. dose


Epinephrine Infusion:
Dose: 2 mcg/min.
Concentration: 4mcg/ml

2mcg x 60gtts/ml
4mcg/ml x min.

30gtts/min. or,
1 drop every 2 seconds

 

[marineman]

For our class we were required to get "Easy 4-step method to drug calculations" by S.D. Foust and brady publishing. It really does make it easy and gives you plenty of practice.