Drug absorption and bioavailability are related concepts in pharmaceutical science, but they refer to different aspects of how a drug behaves in the body.
Drug Absorption: This is the process by which a drug moves from its site of administration (such as the gastrointestinal tract, skin, or respiratory system) into the bloodstream. Absorption is influenced by various factors, including the drug's formulation, route of administration, solubility, and the physiological characteristics of the area where absorption occurs. For example, drugs taken orally must pass through the digestive system, where they are dissolved and then move across the intestinal wall into the bloodstream.
Bioavailability: This term refers to the fraction of an administered dose of unchanged drug that reaches the systemic circulation (the bloodstream) and is available for therapeutic effect. Bioavailability is often expressed as a percentage. It considers not only the absorption of the drug but also the extent to which it remains unchanged during its first pass through the liver (the first-pass effect). For example, a drug with high bioavailability means that a significant portion of it enters the bloodstream intact, allowing it to exert its effects. Bioavailability can vary based on the route of administration (e.g., intravenous administration usually results in 100% bioavailability, while oral administration may result in less).
In summary, drug absorption refers to the process of the drug entering the bloodstream, while bioavailability measures the extent and rate at which the active drug reaches systemic circulation and is available for action.
Pion Inc. offers several different flux platforms to assess passive absorption when combined with our unique Rainbow fiber optic UV-vis, fiber optic-based concentration monitor to measure the concentration of molecules that diffuse through specialized, biomimetic membranes that are representative of the gastrointestinal tract (GIT). Our in vitro tools help pharmaceutical scientists understand flux (a proxy for permeability) of formulations to make predictions about which formulations might show the most desirable absorption characteristics in vivo.
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