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Biopharmaceutics Classification System (BCS)

What is BCS classification?

BCS classification system is a scientific framework to differentiate the drug substances on the basis of solubility and permeability under prescribed condition. 

Where the solubility classification based on a United States Pharmacopoeia (USP) aperture and the intestinal permeability classification is based on a comparison to the intravenous injection. 

According to the BCS classification, drug substances are classified as follows (BCS classification with example): 

  1. Class 1: High Solubility – High Permeability [Example: Amantadine, Diazepam, Itopride HCl, Paracetamol, Zidovudine]
  2. Class 2: Low Solubility – High Permeability [Example: Dexlansoprazole, Ibuprofen, Gefitinib, Etoricoxib]
  3. Class 3: High Solubility – Low Permeability [Example: Baclofen, Dapagliflozin, Empagliflozin Gabapentin, Rabeprazole]
  4. Class 4: Low Solubility – Low Permeability [Example: Aprepitant, Erythromycin Succinate, Sulfasalazine]

Importance of BCS classification system

BCS classification system is an important tool for generic drug development. It’s give a comparative evidence between test product and RLD (reference listed drug). Without BCS classification it's so tough to design a generic drug development. Because the solubility and permeability of API highly impact on BE study. So to reduce the failure of BE study one should be confirmed the API BCS classification.

A drug substance is considered highly soluble when the highest strength is soluble in 250 mL or less of aqueous media within the pH range of 1 - 6.8 at 37 ± 1°C.

A drug substance is considered to be highly permeable when the systemic BA or the extent of absorption in humans is determined to be 85 percent or more of an administered dose based on a mass balance determination (along with evidence showing stability of the drug in the GI tract) or in comparison to an intravenous reference dose.

ICH guidance provides recommendations to support the biopharmaceutics classification of drug substances and the BCS-based biowaiver of bioequivalence studies for drug products. The BCS-based biowaiver principles may be applied to bioequivalence purposes not explicitly specified in the guideline, provided they can be supported by a thorough scientific rationale.


Why select 250 ml media for measuring solubility?

The volume estimate of 250 mL is derived from typical BE study protocols that prescribe administration of a drug product to fasting human volunteers with an 8 fluid ounce glass of water.

What is Log P value?

Log P value indicate the permeability of a material. Higher value indicate the high permeability of the material. Generally, Log P > 1.72 indicate high permeable material. If logP value is more - compound is hydrophobic and if logP value is less - compound is hydrophilic. Most of the time the logP values we get to look in the journal articles or in the in-house medicinal chemistry programs are calculated and not experimental numbers. Therefore, 'c' in clogP stands for 'calculated'.

What is LogD?

which is the measure of distribution co-efficient (similar to partition co-efficient) takes both ionized and un-ionized forms of the compound into consideration. 

(a) Depending on pH, the ratio of ionized/un-ionized form of compound would change.  

(b) Therefore, when log D values are provided, always pH at which the measurement was performed should be indicated. Typically the most interesting is pH 7.4, since the majority of known drugs contains ionizable groups and are likely to be charged at physiological pH.

logD = 0 - 3 (considered as optimal range for lipophilicity) -  Compounds with logD value between 0 - 3 tend to have good solubility and permeability [most favourable for oral absorption and cell membrane permeation]

logD ~ 2 [for CNS projects] - most favourable for blood brain barrier permeation.

logD< 0 [highly hydrophilic] and logD> 5 [highly lipophilic].

What do you mean by very soluble?

A material will be very soluble if 1ml of solvent will dissolve one or more grams of solute.

Which is the reliable bcs classification database in online?


  • Wikipedia
  • ICH guideline
  • EMA

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