How to calculate Assay or Potency of API

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

• 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.

Salt removal or factor adjustment.

Some active pharmaceutical ingredients are used in salt form like Metformin Hcl and some are used without salt like Sitagliptin Phosphate in which phosphate factor is removed from sitagliptin.

• 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.

Calculation For Moisture Content

Suppose we have an API whose potency or assay is 100% and CoA claims that it has 3% Moisture content.

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...

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Potency calculation of API