Importance of Dissolution

-Tablets or capsules taken orally remain one of the most effective means of treatment available. The effectiveness of such dosage forms relies on the drug dissolving in the fluids of the gastrointestinal tract prior to absorption into the systemic circulation. The rate of dissolution of the tablet or capsule is therefore crucial.

-Tablet Dissolution is a standardized method for measuring the rate of drug release from a dosage form. The principal functions of the dissolution test may be summarized as follows:

• Optimization of therapeutic effectiveness during product  development and stability assessment.

• Routine assessment of production quality to ensure uniformity between production lots.

• Assessment of ‘bioequivalence’, that is to say, production of the same biological availability from discrete batches of products from one or different manufacturers.
• Prediction of ‘in-vivo’ availability, i.e. bioavailability (where applicable).

-Dissolution rate may be defined as the amount of solid substance that goes into solution per unit time under standard conditions of temperature, pH, constant solid surface area and solvent composition.

Noyes Whitney Equation:

dC/dt  =  k(Cs – C_b)

Where

dC/dt = dissolution rate of the drug,

k = dissolution rate constant (first order),

Cs = concentration of drug in the stagnant layer (also called as the saturation or maximum drug solubility),            

C_b = concentration of drug in the bulk of solution at time t.