Sink condition

 In pharmacokinetics, the sink condition refers to a scenario in which the concentration of a drug at the site of absorption (e.g., in the gastrointestinal tract) is much higher than its concentration at the site of elimination (e.g., in the blood or plasma). This ensures that the drug continuously moves from the site of absorption to the bloodstream due to a concentration gradient, promoting maximal absorption efficiency.

How it is achieved:

1. High Absorption Rate: By maintaining a high concentration of the drug at the absorption site, either through repeated dosing or sustained release formulations.
2. Rapid Clearance: The drug must be rapidly eliminated or distributed throughout the body once it enters the bloodstream, keeping the concentration at the elimination site low.
3. Maintaining Concentration Gradient: In vitro studies (e.g., dissolution testing) often involve using a large volume of dissolution media to ensure that the drug concentration in the medium stays low, mimicking in vivo sink conditions. This allows continuous dissolution of the drug.

This principle is crucial in drug release and absorption studies, as it helps to mimic realistic in vivo scenarios where the drug moves efficiently from the absorption site to systemic circulation.