Drug Math Tutorial Part IV

Okay, now that you have the correct method to work out any prehospital drug calculation (once you learn it well), I am going to teach you a few tricks and other methods.

The first trick I am going to teach you is for Dopamine. This trick will yield you a starting dose of 5mcg/kg/min using 1600mcg/ml concentration and a mini drip (60gtts/ml). This will give you a starting point to titrate from. It is a pretty easy method and it works every time (well every time I have used it).

1. First, take your patients weight in pounds (that's right, pounds!).
2. Then drop the last number off the weight
3. Then subtract 2
4. This will be your gtts/min.

Lets try it:

148 lbs

drop the last number

14

subtract 2

14 - 2 = 12

12 gtts/min.

Okay, now lets try this with the master formula:

5mcg/kg x 67kg x 60gtts/ml

400mg/250ml x min

5mcg/kg x 67kg x 60gtts/ml

1600mcg/ml x min

5 x 67 x 60gtts

1600 x min

Your answer will come out to 12.5625

Pretty close huh?

Try this with a few other weights and see what you come up with. This is easier than the dopamine clock method, so I am not going to teach that. I will show you the clock for lidocaine though.

The Lidocaine Clock

4mg/ml

Please excuse my horrible drawing. I am going to explain this method for those who have not adopted Amiodarone as the end all save all, and might still have enough Lido to do this. Or for the future, since I have a small feeling that the next set of AHA proposed ACLS guidelines will be bringing Lido right back where it was.

This is how you use the clock method.

Notice how the numbers 15, 30, 45, & 60 all sit in the drawing the same place they would on a clock?

1. First you must mix your bag, 2gm in 500cc, or 1gm in 250cc
2. Use a mini drip (60gtts/ml)
3. This will give you a concentration of 4mg/ml
4. Look up the dose you need per min. (example 2mg/min)
5. Run your dose at the setting according to the clock.

So if your dose is 2mg/min you will run your drip at 30gtts/min. (1gtt/2sec)

If your dose is 4mg you will set your drip at 60gtts/min (1gtt/sec)

Get it? Hope so, its pretty simple.

Another thing I wanted to mention in this part was volume dosages. I kind of touched on this with one of the Q&As for part III. When administering an amount of fluid over time, you can ignore the drug dose in the formula. The math becomes much simpler.

Amiodarone: 150mg in 100cc(D5W) over 10 minutes.

For this medication you want to use a macro drip(10gtts/ml) just because its too hard to count the mini drip dose and most people just end up leaving it wide open (which goes in at about 10 min coincidently).

So for this dose forget the drug portion. You need to get 100cc of fluid in over 10min using a macro drip.

1. For this, just multiply your total fluid by your drip set.

100ml x 10gtts/ml = 1,ooo

2. Then simply divide by the time that you need to get it in.

1,000/10 = 100

answer: 100gtts/min

This is easier than trying to plug it in to the master formula. Plug in a mini drip and see why we don't use that. I think you would have to count 600gtts/min.

Try using these methods in conjunction with the master formula.

• Part 1
• Part 2
• Part 3
• Part 4
• Answer Key