Potency calculation of Active pharmaceutical ingredients is the most common activity which is performed on the daily basis by pharmacists in the pharmaceutical industry. It is a common observation that the majority of pharmaceutical professionals don’t know how to calculate the potency or assay of an active pharmaceutical ingredient.
What is API
- API is the Active pharmaceutical ingredient which gives pharmacological or therapeutic activity.
- Only API is the element in a complete dosage form which gives effect to cure, treat or prevent disease. All other ingredients are called excipients which have no pharmacological effect.
- API is the pharmacological agent so its quantity should always be measured in a precise manner.
- API is delivered according to the label claim.
- To calculate the potency of API following factors are considered.
- Moisture Content of API
- Salt removal or factor adjustment.
Moisture Content
Amount of moisture content in the API is checked in the certificate of Analysis of that specific API and its adjustment is made to maintain its efficacy.
- The question is how will we know that when to use API with salt and when to use API without salt?
The answer to the question is that for this we have to check or read the label claim. If the label claims that each tablet contains Sitagliptin phosphate then we do not need to remove the salt form and if the label claim states that each tablet contains Sitagliptin “as phosphate” then we have to remove the salt form from API.
Many active pharmaceutical ingredients give pharmacological effect with salt form and some API give effect without salt. The attached salt is used just as a carrier to improve solubility or dissolution etc.
How will we adjust M.C Of the API?
Usually, We use 100% of API and in the above case, we have 100% of API and 3% moisture content so, first of all, compensate moisture content as follow
Assay-MC÷100×100
Adding above values in the formula,
100-3÷100×100=97%
our API is 97%.
How to make 97% to 100%?
We have to add 3% extra API to compensate MC and make it 100% or use the following factor to calculate API
100÷(Assay-Mc)
After adding values
100÷(100-3)=1.03
1.03 is the MC or moisture content compensation factor.
Example
In a pharmaceutical company,50 kg API is used to manufacture 100,000 tablets. Each tablet contains 500 mg API and an assay of API is 100%. The moisture content in API is 4%.
Calculate the MC compensation for the above statement.
Use above formula to calculate factor
100÷(Assay-Mc)
100÷(100-4)=1.04
Multiply this factor value to the amount of API in kilograms as follow,
50×1.04=52kg
or add 4% extra quantity of API to compensate MC as follow,
so
50+2=52 kg
Explanation
In simple words, 4% moisture content is present along with API in the above statement and according to by weight calculations, if we weigh 50 kilograms of API then actually 4% of 50 kg is moisture content which is 2 kg so we will add extra 2 kg to compensate moisture content and statement will be as follow
- 52 kg of API with 4% MC is equivalent to 50 kg of API without MC.
Effect of Moisture Content on Assay
If we calculate assay for above statement without moisture compensation and dispense API 50 kg with 100% assay then assay for 50 kg with moisture content is as follow,
Assay of 50 kg is =100%
2 kg is the moisture content so actual API is
50-2=48kg
If we add moisture compensation before dispensing the API then we will dispense 4% more API and the total quantity will be 52 kg.so as we know,
Assay of 48 kg is =96%
then
Assay of 52 kg is =96/48×52=104%
In 104%, 4% is the moisture compensation and 100 % is the assay.
In term of individual tablets, if we take
50 kg and 100% assay then with no moisture content adjustment, each tablet will contain 500 mg API and in each 500 mg tablet 4% is moisture content which is
500×4/100= 20 mg
mean each tablet contains 20 mg less API so it’s assay will also be lower than 100% as,
Assay of a tablet containing 500 mg API is= 100%
Our tablet contains 20 mg less API so
500 mg API – 20 mg API=480 mg API
so
- Assay of a tablet containing 480 mg API is= 100÷500×480=96%
so we will add 4% extra API or multiply 500mg by above-mentioned factor 1.04 to compensate moisture content.
500×1.04=520mg
so
- Assay of a tablet containing 520 mg API is= 100÷500×520=104%
in 104, 4% is the moisture compensation and 100% is assayed.
For salt removal following formula is used
Molecular weight Of API with salt÷Molecular weight of API without Salt
Example
Label claim of a tablet states that each tablet contains Sitagliptin phosphate 50 mg.
then
In the pharmaceutical industry,10 kilograms of sitagliptin phosphate are used to manufacture 200,000 tablets. Strength of the tablet is 50 mg.
How much Sitagliptin phosphate is present in one tablet?
For this
First, of all, convert 10 Kilograms into milligrams
10×1000=10,000 grams
10,000×1000=10,000,000 milligrams
Divide it by batch size as follow, 10,000,000/200,000=50 mg
So each tablet contains 50 mg of sitagliptin phosphate.
Now let’s take the above statement in another way as,
Label claim of a tablet states that each tablet contains Sitagliptin as phosphate 50 mg.
then look at another example.
Examp
In a pharmaceutical industry 10 kg, Sitagliptin phosphate is used to manufacture 200,000 tablets. Strength of tablet is 50 mg
How much Sitagliptin phosphate is present in one tablet?
First of all convert kilograms into milligrams as follow
10 ×1000 =10,000 grams
10,000×1000=10,000,000 milligrams
Divide it by batch size as follow,
10,000,000/200,000=50 mg
So each tablet contains 50 mg of sitagliptin phosphate.
But according to the above statement, we need sitagliptin 50 mg, not sitagliptin phosphate so we will remove phosphate. (Focus on the term “as phosphate”)
How will we do that?
According to the above statement, the pharmacological effect is produced by sitagliptin, not by sitagliptin phosphate.
So how will we remove phosphate attached with sitagliptin?
One explanation is that Physically we can not separate phosphate from sitagliptin so add compensation factor like moisture content. So extra weight of API is added in the formulation.
The Molecular weight of sitagliptin with phosphate÷Molecular weight of sitagliptin without phosphate
after adding values
505.31 g/mol÷407.31 g/mol
=1.24
1.24 the factor for salt removal or factor adjustment.
so
Multiply the factor with total API in kilograms or with the strength of individual tablet as follow,
10 kg × 1.24=12.4 kg
or
50 mg × 1.24 = 62 mg/tablet
From the above statement, it is clear that to remove phosphate from sitagliptin we have to use 12.4 kilograms of Sitagliptin phosphate instead of 10 kilograms of sitagliptin phosphate.
so
12.4×1000×1000÷200,000=62 mg
In label claim, it is written as
Each tablet contains 62 mg of sitagliptin phosphate equivalent to 50 mg of sitagliptin.
Mean 12 mg is the phosphate and 50 mg is the sitagliptin.
How to calculate the %age of API in a given formulation?
Each tablet contains sitagliptin as phosphate 25 mg.
Find the %age of active pharmaceutical ingredient in the given formulation.
Manufacturing Order
Product Name = Z 25 mg
Batch Number = Y
Batch Size = 200,000 Tablets
Ingredient |
Unit |
Quantity |
Sitagliptin Phosphate |
kg |
6.324 |
Avicel PH 101 |
kg |
11.276 |
PVP K 30 |
kg |
0.800 |
Ac-di-sol |
kg |
1.200 |
Aerosil |
kg |
0.100 |
Mg Streate |
kg |
0.300 |
Total weight is = 20 kg
Tablet weight is 100 mg
How to Find the %age of active pharmaceutical ingredient?
To find the %age of API in the above formulation following procedure is used.
First of all convert kilograms of API into milligrams as follow
- 6.324×1000×1000=6324,000 mg
Divide the number of milligrams by batch size as following
6.324×1000×1000=6324,000 mg÷200,000
= 31.62 mg
Now divide it by tablet strength which is 25 mg in the above case so
31.62÷25=1.2648
As we know from label claim that we have to remove salt so use the following formula.
Molecular weight of sitagliptin with phosphate÷Molecular weight of sitagliptin without phosphate
after adding values
505.31 g/mol÷407.31 g/mol
=1.24
-
Now divide 1.2648 by 1.24 as
1.2648÷1.24=1.02
-
For %age multiply 1.02 by 100 as
1.02×100=102%
Result
In the above formulation API %age is 102%.
Active pharmaceutical ingredients in a pharmaceutical product are always used after proper adjustments for moisture content and salt removal
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What would be the potency calculation for Ciprofloxaxin HCl.
Bulk batch size 153.300 Kg.
Tablet weight 730 mg
Label claim 500 mg as Ciprofloxacin
Your API is ciprofloxacin Hcl?
What is the weight of API in kg?
From label claim, it seems that your API is ciprofloxacin Hcl and label claim states that each tablet contains ciprofloxacin as HCl. So we will have to remove salt and find the factor for salt compensation as follow
Molecular wt of ciprofloxacin Hcl÷molecular weight of ciprofloxacin
Add values
367.8/331.133=1.110
So 1.110 is salt removal factor
Multiply it with tablet potency
500×1.110=555 mg
Mean 555mg of ciprofloxacin hcl is equivalent to 555 mg of ciprofloxacin.
210,000×555=116.55 kg
So your API should be 116.55 kg if it's 100%.
*555mg of ciprofloxacin hcl is eq to 500mg of ciprofloxacin
Is there any additional water added with Ciprofloxacin HCl?
additional water for?
you mean for kneading?
I mean as a compound. As monhohydrate or dihydrate?
monohydrate available
Can you mention a reference for more information?, thanks.
Love it..the way its written..
thanks
Thanks… Very informative…
I want to know about assay on as such basis, Assay on anhydrous basis ?
when to use that means, criteria for usage in formulation?
When to not calculate assay in formulation?
If two AR no of different assay used in product what is the calculation formula
(Balance Qty of API/LABEL CLAIM x Assay/100 x 100-LOD/100 X 1000 X 1000 FOR FIRST A R NUMBER
LABEL CLAIM X 100/ASSAY X 100/(100-LOD) X B.SIZE /1000 X 1000 FOR SECOND AR NUMBER
Can anyone share with me the calculations and master formulation of paracetamol in a pharmaceutical industry?
Sir you missed the way of calculation of quantity of api during dispensing when two batches or lots to be used. Please guide
thanks i will add soon
Excellent explanations,really Loved it, this will be helpful for Most of Formulations people….