Monday, October 22, 2012

Dosage Math

Medication Labels are confusing. Sometimes after reading one, I stand there and scratch my head wondering what in the world were these people trying to communicate?
 It should not be a surprise they are not clear. After all, they were written by research scientists and then edited by lawyers and FDA bureaucrats.  Maybe the miracle is that we can make sense out of them at all.
Add to that the language of mg/lb, mg/ml, cc, % and it is easy to get confused.
I hope that this will help you decipher the gibberish and give the pigs the right dose.
The good news is that new products like Draxxin have dosage charts right on the label which makes it pretty straightforward to figure out how much to give.

The bad news is that for most older products it is just too expensive to update the labels. As silly as it seems if Pfizer said they wanted to make the LA 200 label as clear as the Draxxin label FDA would make them go through almost as much hassle as if LA200 were a brand new drug.
So let’s go through some of the terms and math and conversions.  
One of the most common things that people ask is, “What is the difference between a cc and an ml?” The two are the same. The abbreviation ml stands for milliliter or 1/1000th of a liter and cc stands for cubic centimeter. A cc and an ml of water both weigh 1 gram. Just use the two abbreviations interchangeably.
So to determine how many cc’s to give the animal you need to know three things:
1.       The weight of the animal
2.       The concentration of the drug
3.       The recommended dosage per lb or kg.
Drug concentration is either expressed as IU /ml, mg/ml, or as a percentage.  IU stands for international unit and I think penicillin is the only thing that is still measured in IU’s. The abbreviation mg stands for milligram and is 1/1000th of a gram. For medications that express their concentration as a percentage are usually water medications but if you want to convert percent to mg/ml it is easy as pie. Just convert the percent to a number and then move the decimal three places to the right. So a 1% solution is a concentration of 10 mg/ml.
Most medications will say the recommended dosage as mg/lb but a few still use mg/kg. There are 2.2 lbs in a kilogram so to convert a mg/kg dose to mg/lb just divide by 2.2.   
So as an example let’s say we want to give a 180 pound pig a dose of LA 200. The LA 200 bottle has two doses listed:
A.      9 mg/lb if we want to give one shot that is therapeutic for three days or
B.      3-5 mg/lb repeated daily.
We are going to give this pig the 9 mg/lb dose so we don’t have to repeat it.
The Math:  9 mg/lb multiplied by 180 lbs = 1,620 mg, which is the total dose for the pig. LA 200 is 200 mg/ml so 1,620 mg divided by 200 mg/ml = 8.1 ml  
Remember only 5 ml per injection site. 

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