# Potency or Assay Calculation in Pharmaceutical Industry

Potency of drug means amount of drug needed to produce an effect of given intensity. It also indicate the maximum response which can be achieved with a drug.

#### Potency Calculation of API for Batch Quantity

• Quantity of API required (from single lot) = (Theoretical Quantity of API ÷ Working Assay of API) X 100 = X kg
• Quantity of API required (from two lots) = [(X-Y) X Working Assay of API (1st Lot)]/ Working Assay of API (2nd Lot)

Here, X = required quantity of API form 1st lot, Y = actual quantity of API found from 1st lot.

#### Potency or Assay Calculation of API (As is Basis, Dried Basis & Anhydrous Basis)

Potency/Assay on as is basis = Sample area x standard concentration/ Standard area x sample concentration x potency or Assay of Standard or Standard Quantity of API ×  100/(Assay on as is basis)

Assay on dried basis = Standard Quantity of API×(Assay on as is basis ×100)/((100-LOD))

Assay on anhydrous basis = Standard Quantity of API×(Assay on as is basis ×100)/((100-Water Content))

#### Common Formula of Assay Calculation

% Content of API = (Asample × Wstandard × Dfactor × Cfactor_1 × Average weight of tablet/capsule × Pstandard × 100) ÷ (Astandard × Wsample × Cfactor_2 × 100 × Label claim)

Here, A = Area/Absorbance, W = weight in mg, P = potency in %, D = dilution, C = conversion.

#### Assay Calculation Formula (HPLC method)

% Content of API = (Asam x Wstd x 200 x Pstd x Twt x 100) ÷ (Astd x 200 x Wsam x 100 x LC)

Here,

Asam = Area of API peak in sample solution.

Astd = Av. area of API peak in standard solution-A.

Pstd = Potency of API working standard (as it is) in %.

Wstd = Weight of API working standard in standard solution-A in mg.

Twt = Target weight of sample, in mg.

LC = Label claim of drug product.

#### Assay Calculation Formula (AAS method)

% Content of API = (0.001 x C x  100 x 100 x 250  x Twt  x  100) ÷ (Wsam  x  5  x  3  x  LC)

Here,

0.001 is the conversion factor from ppm to mg/mL.

C = Concentration of sample.

Wsam = Weight of sample (in mg).

LC = Label claim of API in mg per tablet.

Tw = Target weight of sample, in mg.

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