1 | The Secret Tool for Quality Compounds: The Certificate of Analysis
Reprinted from the 2015 July Apothagram
THE SECRET TOOL FOR QUALITY
COMPOUNDS: THE CERTIFICATE OF
ANALYSIS
www.eagleanalytical.com
Reprinted from 2015 July Apothagram | © PCCA 2015
One of the most indispensable pieces of information a compounder needs with every active pharmaceutical
ingredient (API) is the certificate of analysis (CofA). In testing compounds at Eagle Analytical, we find that one
of the most significant reasons for out of specification (OOS) preparations is because pharmacists do not consult
the CofA.
As compounders, we have to pay particularly close attention to the information it contains, because it could
alter the way we compound our final preparations.
Here we will briefly explain what a CofA contains, how to use it in compounding and provide several examples
to illustrate areas where errors in compounding could occur if it were not used. Keep in mind the CofA for each
chemical is lot number specific, meaning two different lots for the same chemical can yield different results even
though it meets the USP requirements.
While the CofA contains a host of information, there are four primary areas that should always be consulted first.
1. Chemical name and chemical abstracts service (CAS) number
Every chemical is given a unique CAS number that specifically identifies the chemical formula (the only exception
is polymers).
Your CAS number is important because sometimes the name listed is a poor representation of the actual
chemical. It may be abbreviated or just incorrect all together. The CAS number and the chemical name have a
one-to-one correspondence. So if in doubt, look up the CAS number to make certain of the exact chemical name.
This is very important in instances where a salt form of the chemical may be confused with the base or for
chemicals with water of hydration in the formula. For example fentanyl is different from fentanyl citrate and
likewise magnesium sulfate trihydrate is different from magnesium sulfate heptahydrate.
2. Description
This is your first line of defense to ensure you have received a quality chemical. The description contains an
explanation of what the chemical looks like, if it has a characteristic odor and if it exhibits any identifying unique
observable characteristics.
If you open the chemical and it is a fine white powder with black specs, but the CofA says it should be a fine
white powder, you know immediately that this should be concerning for the chemical. In a similar manner, a
foul smell for something that should have a faint citrus odor is an instant tip off that the chemical may need to
be set aside and not used.
www.eagleanalytical.com
Reprinted from 2015 July Apothagram | © PCCA 2015
3 | The Secret Tool for Quality Compounds: The Certificate of Analysis
3. Assay
This is the pure API amount of the chemical that you have, or in some cases, like antibiotics, it’s the biological
activity per weight of the material. This may be expressed in activity units, as with hyaluronidase (723 IU/
mg) where the chemical has been compared to an industry standard and assigned an international unit (IU)
designated assay or strength.
In order to ensure you are weighing out the correct amount of the API, make sure to use the unique percentage
or unit number in your formulations. If the assay is 98.5% you will need to weigh out 1.5% more of the API than
what your formula calls for in order to get the correct potency in your compound.
For most APIs the assay is between 98% and 103% and is usually ignored but you really can’t afford to do that.
T3, for instance, can be as low as 95% and still be within USP specifications. If you don’t account for this in your
compounded preparations, then your potency could be thrown off.
4. Water
Expressed as (1) water of hydration, which is water that is a part of the chemical formula rather than water that
has been absorbed, and/or (2) loss on drying (LOD) which indicates the amount of moisture that the API has
absorbed in the manufacturing and storage process. For example, a specification with an LOD of 6.3% means
that when you weigh out 100 mg of the material, 6.3 mg is really water.
A high LOD means that the chemical has a propensity to absorb water. If stored incorrectly, or you live in a
geographic area with high humidity, then this chemical could continue to pick up water and result in an underpotent API.
Make sure to check this on your CofA every time and remember it could change based on LOT and still be
within the USP requirements. Using a T3 example, a USP certified T3 can have up to 4% absorbed water and still
be within the USP guidelines.
Calculations to apply
Now that you have reviewed your CofA and know your API’s chemical name, CAS, assay, amount of water
and/or LOD, now we need to go over the three calculations that you may need to adjust the final
compounded preparation.
Think of these calculations in logical order:
1. Remove or account for the water
2. Solve for the API you have left in the remaining chemical
3. D
ecide if you need to correct for the salt in the chemical since the formula calls for the base
Remembering these three steps in this order will remind you that the salt base conversion is performed with the
molecular weights (MW) of the chemical without the water.
www.eagleanalytical.com
Reprinted from 2015 July Apothagram | © PCCA 2015
4 | The Secret Tool for Quality Compounds: The Certificate of Analysis
Calculation 1: Water Correction
Water (or LOD) is usually expressed as a percentage on the CofA, such as 7% water. This means that
proportionally every 100 mg of the chemical actually has 7.0 mg of water.
The water correction factor to apply is [(100-Water%)/100] g/g chemical. Let’s apply this formula to a theoretical
lidocaine HCl monohydrate lot we received where the CofA lists a water concentration of 7%. The water
correction factor would be: (100/(100-7.0)) = 1.075.
Even though you could get a pretty good estimate of the water correction factor by using the molecular weight
(MW) for those APIs that are hydrated, there are always small differences between that theoretical number and
an actual determination as reported in the CofA. Using the MW of lidocaine HCl monohydrate, the water factor
formula would look like this (288.81/(288.81-18)) = 1.066 and result in a difference of 0.009
Since USP allows lidocaine HCl monohydrate to have between 5% and 7% water, the most accurate correction
would therefore come from the CofA.
Calculation 2: Assay Correction
Calculate the amount of API in your chemical with the assay correction. Most assays assigned in the CofA are
done after the water has been removed (on an anhydrous basis). In essence, the API is dried and then a chemical
analysis is performed on the chemical to determine the amount of pure API that is in the particular lot. Most
USP monographs only allow a very narrow band of acceptability, but there are cases where the acceptable range
can be quite large, especially in biologics and antibiotics.
Most of the time, the assay information given on the CofA is listed as a percentage, therefore, making it easier
to calculate. Sticking with the example chemical, lidocaine HCl monohydrate that we used above, let’s say the
actual assay was 98.0% (which is within the USP monograph range of 97.5% to 102.5%); this means that the API
has only .98 gm of API per gm of chemical. The correction factor to apply on your compounded preparation
should be (100/98.0) = 1.020.
Calculation 3: The Salt to Base Corrections
First determine what the prescription is requesting. Unfortunately, some prescribers do not take into account the
subtle and not so subtle differences in casual name and exact name of an API. If ever in doubt, always contact
the practitioner first and have the USP monograph on hand when discussing with them. As always make sure
you are labeling the prescription correctly. For example, don’t label a prescription lidocaine 1% if you made it
with 1% of the hydrochloride salt. Instead label it lidocaine HCl 1%.
Once you feel confident that the correct chemical is identified, the next step is to correct for the proper weight of
the chemical. This conversion is obtained by the MWs of the base and salt form of the API. The ratio of these two
MWs will provide the correction factor to apply.
Example using lidocaine HCl monohydrate: use the MW of the lidocaine (MW 234.32 g/mole) and the lidocaine
HCl (MW 270.80 g/mole), not the hydrated lidocaine HCl monohydrate (MW 288.81 g/mole). So if you
have lidocaine HCl monohydrate and need the lidocaine base, the conversion formula for the salt to base is
(270.80/234.32) = 1.156.
www.eagleanalytical.com
Reprinted from 2015 July Apothagram | © PCCA 2015
5 | The Secret Tool for Quality Compounds: The Certificate of Analysis
Now that you have these three calculations, all generated by your API’s CofA, you can continue on with
other calculations to further ensure the potency of your compounded preparation.
Chemical Weight = Remove Water, Correct for Assay and then Correct for Salt / Base (if needed).
Therefore: Chemical Weight = API Weight x Water Conversion x Assay Conversion x Salt Conversion (if
needed).
For the lidocaine HCl monohydrate to lidocaine base the result using the example above would be:
Weight Lidocaine HCl Monohydrate = Lidocaine API Weight Needed x 1.075 x 1.020 x 1.156 = Lidocaine
Weight Needed x 1.268
Using just the MW for the conversion would give us a theoretical result of:
Weight Lidocaine HCl Monohydrate = Lidocaine Weight Needed x (288.81/234.32) = Lidocaine Weight
Needed x 1.233
Just to further confuse matters, there are preparations that do not require a correction for the salt form or water
content of the chemical. The most notable being morphine sulfate injection, which is made with morphine
sulfate pentahydrate, and the potency of the injection is based on morphine sulfate pentahydrate. The USP
monograph for morphine sulfate injection specifies that it should contain not less then 90% and not more than
110% of morphine sulfate pentahydrate. So when compounding with this API you do not need to adjust for the
water content or the salt form of the chemical. Always consult the USP for the applicable monograph.
Since all these corrections will most likely need to be done for the same preparation, the corrections can be applied
in any order or in one step. However, in most cases you will need to take into account the chemical assay and the
water, either absorbed or in the chemical formula, to get the correct amount of the API in your preparation.
Compounding software, like PCCA’s PK Software, if set correctly, automatically makes these adjustments for you.
All you need is the CofA when you are inventorying your chemicals into the system.
www.eagleanalytical.com
Reprinted from 2015 July Apothagram | © PCCA 2015