Question

Decrease in effective surface area available to the dissolution medium leading to a fall in the dissolution rate, may happen due to which one of the following reasons? 

• A. Addition of cyclodextrin
• B. Addition of surfactant to increase the surface tension
• C. Addition of hydrophilic diluent
• D. Surface charges due to extreme particle size reduction

Answer 1

The Correct Option is D

The question addresses the factors affecting the dissolution rate of a substance, focusing on how a decrease in the effective surface area available to the dissolution medium can affect the dissolution rate. Let's analyze each option:

1. Addition of cyclodextrin: Cyclodextrins can form inclusion complexes with hydrophobic drugs, effectively increasing the solubility and thereby potentially increasing the dissolution rate. Hence, this option does not cause a decrease in the effective surface area.
2. Addition of surfactant to increase surface tension: Surfactants generally act to decrease surface tension rather than increase it. Decreased surface tension usually improves the dissolution by allowing better wetting. Thus, this option is unlikely to result in a decline in the dissolution rate.
3. Addition of hydrophilic diluent: Hydrophilic diluents usually help improve wettability and dissolution rates. Therefore, this option is not responsible for a decrease in the dissolution rate. 
4. Surface charges due to extreme particle size reduction: When the particle size is extremely reduced, it can lead to increased surface charges that might cause particle agglomeration. This aggregation reduces the effective surface area available to the dissolution medium, hence decreasing the dissolution rate. This mechanism is well recognized in pharmacology and pharmaceutical sciences.

The correct answer is Surface charges due to extreme particle size reduction because it directly results in a decrease in the effective surface area available to the dissolution medium, negatively impacting the dissolution rate.

To conclude, understanding the balance between particle size, surface charge, and dissolution rate is crucial in formulation sciences, particularly in drug formulation and development.