The other night we had an “incident” that resulted in a large gash in the front leg of my best polo pony. Why is it always your favorite horse?

One expensive, after hours vet call later and a bunch of stitches, the vet left me with a list of medications to be administered over the next two weeks. Some of those are topical. Some are oral. And others are injectable.

I think most of us have a tendency to administer medication dosages from memory. But my memory for numbers is not that good. So, not wanting to make a big mistake, I always check the labels on the bottle. However, you may have discovered, like I did, that the dosage instructions are not as easy as one might think.

The picture below is the label for injectable Bute (Phenylbutazone). In order to determine the proper dosage, you have to do a little bit of higher math.

Given the labeling on most medications, it takes four variables to determine the proper dosage for your horse. Those variables are: 1) how many milligrams; 2) per how many pounds; 3) the weight of the horse in pounds; and 4) how many milligrams of the drug there are per milliliter. Knowing those four numbers will give you the dosage in millimeters, which is the unit of measure on a typical syringe.

To make this easier, my husband made me a little spreadsheet to make sure I get medication dosage calculations right. So let me take you through an example using this bottle of Bute.

In this case, the bottle says to give 1 to 2 grams per thousand pounds of body weight. Since we are trying to get to milligrams, we convert 1 gram to 1000 milligrams in the first column. (if we were going with the higher 2 gram dosage, it would be 2000 milligrams.)

In the second column, we know that it is per thousand pounds of body weight. In this example we will assume that our patient weighs 1100 pounds. That goes in the third column.

The last piece of information is how many milligrams per milliliter. In this case, it is 200. See the photos of the bottle to confirm these numbers.

So, to determine the proper dosage, the formula is (milligrams / by per pound) * (weight in pounds / milligrams per milliliter).

Using the numbers from our example, it would be (1000/1000) * (1100/200) = 5.5 ml.

Whew! That is a lot of math just to figure out the correct dosage for medication. But it is important math. You can’t make assumptions.

Let’s say you usually use Bute as an anti-inflammatory. Now you switch to Equioxx, which is also an anti-inflammatory. We just calculated the proper dosage of Bute as 5.5 ml. If you give that same dosage of Equioxx, you would be double dosing the horse.

Medication dosages in polo seem to be a little bit of tribal knowledge. They just get passed on from person to person. But if you want to really be sure, do the math.

That is what I learned today. But I am lucky enough to have a math whiz, for a husband, who made me the spreadsheet. How do you do it? As always, comments and questions are welcome.