Liberation (pharmacology)

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Liberation is the first step in the process by which medication enters the body and liberates the

. As the stomach has an aqueous environment, it is the first place where the pill can dissolve. The rate of dissolution is a key element in controlling the duration of a drug's effect. For this reason, different forms of the same medication can have the same active ingredients but different dissolution rates. If a drug is administered in a form that is not rapidly dissolved, the drug will be absorbed more gradually over time and its action will have a longer duration. A consequence of this is that patients will comply more closely to a prescribed course of treatment, if the medication does not have to be taken as frequently. In addition, a slow release system will maintain drug concentrations within a therapeutically acceptable range for longer than quicker releasing delivery systems as these result in more pronounced peaks in plasma concentration.

The dissolution rate is described by the

Noyes–Whitney equation

:

${\displaystyle {\frac {dW}{dt}}={\frac {DA(C_{s}-C)}{L}}}$

Where:

• ${\displaystyle {\frac {dW}{dt}}}$ is the dissolution rate.
• A is the solid's surface area.
• C is the concentration of the solid in the bulk dissolution medium.
• ${\displaystyle C_{s}}$ is the concentration of the solid in the diffusion layer surrounding the solid.
• D is the diffusion coefficient.
• L is the thickness of the diffusion layer.

As the solution is already in a dissolved state, it does not have to go through a dissolution stage before absorption begins.

Ionization

Cell membranes present a greater barrier to the movement of ionized molecules than non-ionized liposoluble substances. This is particularly important for substances that are weakly

References