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.