Question

Select the equation that gives the rate of drug dissolution from a tablet

• A. Fick's law
• B. Henderson Hasselbach equation
• C. Noyes Whitney Equation
• D. Michaelis Menton equation

Answer 1

The Correct Option is C

To determine the rate of drug dissolution from a tablet, we rely on the Noyes-Whitney Equation. This equation is specifically designed to describe the dissolution rate of solid substances into a solvent, which is a crucial step in the pharmacokinetics of oral dosage forms like tablets.

Let's examine and understand why the Noyes-Whitney equation is the correct choice and how it contrasts with the other options:

1. The Noyes-Whitney Equation is expressed as: \[\frac{dC}{dt} = \frac{DA(C_s - C)}{L}\] Where:
   • \( \frac{dC}{dt} \) is the rate of dissolution.
   • \( D \) is the diffusion coefficient.
   • \( A \) is the surface area of the solid.
   • \( C_s \) is the saturated concentration of the drug in the solvent.
   • \( C \) is the concentration of the drug in the solvent at time \( t \).
   • \( L \) is the thickness of the diffusion layer.
   This equation helps in identifying how quickly a drug will dissolve in the body, which is vital for the drug's effectiveness. Hence, it is the correct answer.
2. Fick's Law describes the diffusion process, particularly focusing on the rate of diffusion across a concentration gradient. While it relates to how substances move, it does not specifically apply to the dissolution rate of a tablet.
3. The Henderson-Hasselbalch Equation is used to estimate the pH of a buffer solution. It relates to the dissociation of acids/bases in a solution and not the dissolution of a substance into a solvent.
4. The Michaelis-Menten Equation describes the rate of enzymatic reactions and is not related to the dissolution process of a drug from a tablet.

By understanding the context and design purpose of the Noyes-Whitney equation, it is evident that it primarily addresses the dissolution rate of drugs from tablets, making it the correct option for this question.