Help with math.

I find myself teaching people pharmacology math a lot.  It's a subject a lot of people approach with fear, but if you can let go of the fear and bear with me, I can definitely teach you:

It all comes down to this:

Divide what you WANT by what you HAVE:

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If you WANT 300mg and you HAVE 150mg tablets:
Divide 300mg by 150mg (300 / 150) = 2 tabs

To double-check yourself, reason it out:
The tablets are 150mg each.  So, if you give 1 tablet, that's 150mg.  If you give a second (150mg + 150mg) that's 300mg and that's what you want.  So, you need 2 tabs.
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If you WANT 800mg and you HAVE 100mg/ml solution:
Divide 800mg by 100mg/ml (800 / 100) = 8ml

Again, use reason to double-check:
The solution is 100mg/ml.  That's 100mg in each ml.  So, the first ml is 100mg, add another ml and get 200mg, add a third, you get 300mg, etc until 800mg at 8ml.
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Now, let's try less easy numbers:

You need to give 144mg.  You have 16mg tablets.  How many do you need?

Want = 144mg.  Have = 16mg.  144 / 16 = 9 tabs.
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You need to give 42mg.  You have 14mg/ml solution.  How many ml do you need?

Want = 42mg.  Have = 14mg/ml.  42 /14 = 3ml.

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How many 75mg Rimadyl tablets does Fluffy need if he was prescribed 225mg per dose?

Want/Have.  225 / 75 = 3 tabs.

Be careful not to switch your WANTS and HAVES!

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Kitty needs 0.06mg of Bupernorphine per dose.  You have 0.3mg/ml Bupernorphine.  How many ml does Kitty get per dose?

Want/Have.  0.06 / 0.3 = 0.2ml

Reasoning this one out is a bit harder, but is still possible if you move the decimal 2 places to avoid dealing with such small numbers.  If you do this you end up needng 6mg of Bupernorphine and you have 30mg/ml.  The first ml is 30mg.  Whoa!  Too much!  We only need 6mg!  So, a half of a ml (0.5ml) is 15mg.  Half of that is a quarter ml (0.25ml), 7.5mg -close, but too much.  Half of that is an 8th of a ml (0.12ml) and 3.8mg -too little.  So, the answer is somewhere between 0.25ml and 0.12ml and closer to 0.25ml.  This matches up with what we got!

If you are a little better with math you may have noticed in the above reasoning that at the first step 1ml, 30mg is 5 times what we need.  This means you need a 5th of a ml which is 20% or 0.2ml.  If you don't see that right away, that's ok.  The long way still works and math comes back the more you practice!

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The last one was a hard one.  Did you get it?  Contact me in the comments or on Facebook with any questions!