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If
necessary, first convert all measurements to the same unit of measure.
For example, if the dosage is in mg/kg (milligram per kilogram)
and your ferret weighs 3.3 pounds, convert the pounds to kilograms (kg).
Do this by dividing 3.3 pounds by 2.2 (since 1 kg =
2.2 lbs):
3.3 lb ¸
2.2 = 1.5 kg
Therefore, your ferret weighs 1.5 kg.
Now you can calculate the amount (in mg) needed since the dosage
is expressed as mg/kg.
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Multiply
the weight by the dosage:
For example, the dosage for tylosin is 10 mg/kg. Multiply this by the weight of your ferret, 1.5 kg in the
example above:
1.5 x 10 mg/kg = 15 mg
Therefore, your ferret requires a dose of 15 mg of tylosin
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How
to calculate the dose from a concentration:
Let’s say you have a bottle of tylosin with a concentration of 30mg/ml
(30 mg of tylosin in every 1 ml of solution).
To figure out how much of the solution to give your 1.5 kg
ferret, simply divide the dose by the concentration:
15 mg ¸
30mg/ml = 15 ¸ 30 = 0.5
Therefore, you give your ferret 0.5 ml of solution
It
seems that the most common value used in dosages and doses is mg.
Sometimes you might find a dosage that’s expressed in micrograms (µg
or mcg). You can easily convert
the microgram to milligram by moving the decimal point three places to the
left. For example, 100 µg =
.100 mg. So, if you have a
dosage of 200µg/ml, that equates to .200mg/ml.
Exercise:
As
a heartworm preventative, ivermectin can be used with an oral dosage of 6 µg/kg.
How much ivermectin would you give a 3.3 pound ferret?
-
Convert
ferret weight to kg: 3.3 lb = (3.3 ¸
2.2)kg = 1.5 kg
-
Convert
µg to mg: 6 µg = .006 mg
-
Multiply
weight by dosage: 1.5 kg x .006 = .009 mg
-
A
1.5 kg ferret requires 0.009 mg (9 µg) ivermectin
The Solution to Percent Solution
Some
concentrations are written as “percent solution.” A good household example is hydrogen peroxide.
It typically comes in a 3% solution.
What does that mean?
Percent
solution means what percentage of 100 grams of a drug is in 100 milliliters
of solution. Getting back to
the hydrogen peroxide, 3% of 100 grams equals 3 grams; therefore, there are
3 grams of hydrogen peroxide in 100 ml of solution.
You could say percent solution is defined as P x 100 g /100 ml, where
P = percent in decimal format (e.g., 10% = 0.10). For example, a 100% solution means 1.00 x 100 = 100 grams in
100 ml, 50% solution means 0.50 x 100 = 50 grams in 100 ml, 1% means 0.01 x
100 = 1 gram in 100 ml.
Since
ferrets are small animals and usually require drugs in very small quantities
like milligrams and milliliters, let’s now see how to calculate how much
of a drug is in just 1 milliliter of solution.
This is actually very easy and doesn’t require any calculations.
One
gram equals 1000 milligrams. If
we have a 1 % solution, that means there are 1000 milligrams of the drug in
100 milliliters, which is defined as 1000mg/100ml.
Simple math tells us we can cancel out an equal number of zeroes and
end up with: 1000mg/100ml, which equals 10mg/1ml.
Therefore, there are 10 milligrams of the drug in 1 milliliter of
solution. Now, compare the
resulting 10 milligrams and the original
1 %.
You’ll notice that if you move the decimal one place to the right
on the percent value you get 10. So,
the simple no-calculations way of determining how many milligrams are in 1
milliliter of any given percent solution is to move the decimal one place to
the right in the percent value.
For example: 3 % solution =
30mg/ml, 12
% = 120mg/ml, 1.5
% = 15mg/ml, and so on.
Solving Dissolving Tablets
Calculating how much water to mix a crushed tablet in
to give a desired dose volume is very easy.
All you do is multiply the amount of the drug (concentration) in the
tablet (mg) by the desired dose volume (ml), and divide that by the desired
dose (mg). The result will be
how much water to add to the tablet.
Let’s say C1 = concentration in the tablet, C2 =
desired dose, V1 = desired dose volume, and
V2 = amount of water to add. The formula is:
C1 x V1 = V2
C2
Suppose you need to give your ferret 1 mg of
famotidine but you want to make it quick and easy by giving only 0.25 ml of
solution (in other words, 1mg/0.25ml).
Pepcid AC tablets contain 10 mg of famotidine.
Multiply the 10 (mg) by 0.25 (ml), divided by 1 (mg), which equals
2.5. Therefore, you mix the
crushed tablet with 2.5 ml water to yield a 1mg/0.25ml solution.
Another example.
Your desired solution is 1.25mg/0.5 ml famotidine:
C1 = 10 mg
C2 = 1.25 mg
V1 = 0.5 ml
V2 = X
10mg x 0.5 ml = X
1.25mg
5
= 4 ml
1.25
Therefore, you add 4 ml water to one 10 mg tablet of
Pepcid to yield a solution of 1.25mg/0.5ml.
The End :)
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