When a drug (medicine) is swallowed (Solid dosage form e.g. tablets, capsules) the absorption of the drug into the body depends mainly on two factors:

a) Solubility: The drug dissolves in the stomach and intestinal fluids 

b) Permeability: The drug readily passes through the intestinal wall into the blood flow 

 

The solubility and permeability are among the main factors that govern the rate and extent of drug absorption and therefore are directly related to Bioavailability of drugs.

The four possible categories for a drug (medicine) according to the BCS are in

Class I -     High Permeability and High Solubility

Class II -    High Permeability and Low Solubility

Class III -   Low Permeability and High Solubility

Class IV -   Low Permeability and Low Solubility

 

High solubility in this system refers to the highest dose of the drug dissolving in 250 mL or less of aqueous media between pH 1 to 7.5. 

BCS class I and class III drugs are highly soluble regardless of pH condition contain Immediate Release (IR) solid oral dosage forms.

High permeability means more than 90% of the dose is absorbed (compared to the same dose taken from IV route).

The multiple factors of the environment  such as pH, surfactant content, etc. of class II and class IV drugs has a huge impact on drug dissolution in the aqueous solution. Hence, the selection of dissolution media and pH condition for in vitro dissolution studies of those drugs will be one of key factors to predict in vivo studies.

 

Bioequivalence/Relative Bioavailability:

Bioequivalence or relative bioavailability is the comparative study of products containing the same drug administered by the same route. Two products are considered bioequivalent if, when administered to the same individual under the same experimental conditions and at the same molar dose do not differ significantly from the amount of drug absorbed and the rate of absorption process. 

 

• Expands the regulatory application of the BCS and recommends methods for classifying drugs.

• Explains when a waiver for in vivo bioavailability and bioequivalence studies may be requested based on the approach of BCS.

 

The insertion of the Biopharmaceutical Classification System (BCS) in Rule 2 after clause (a) Drugs and Cosmetics (Ninth amendment) Rules 2017* has become an important tool to set a standard for regulators and pharmaceutical industry. 

As per the Notification the applicant shall submit the result of bioequivalence study referred to in Schedule Y of Drugs and Cosmetics Rules 1945, along with the application for grant of a licence of oral dosage form of drugs specified under category II and category IV of the biopharmaceutical classification system to get licences under the Form 25, Form 25F, Form 25A, Form 28, Form 28B, Form 28D and Form 28A.

Moreover we assume that as per new amendment in rules the applicant shall submit bioequivalence study waiver request along with application for new generic medicines containing drugs belonging to BCS Class I and class III.