Passive membrane permeability, drug flux, and oral absorption

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Karl Box
Dec 18, 2023
min read
Passive membrane permeability, drug flux, and oral absorption

Passive membrane permeability, drug flux, and oral absorption are concepts related to the movement of drugs across biological membranes, particularly in the context of oral drug administration.

Passive membrane permeability refers to the ability of a substance, such as a drug molecule, to pass through biological membranes without the need for energy input (i.e., without active transport). Factors influencing permeability include lipophilicity, molecular size, charge and hydrogen bonding.

Drug flux can be described by Fick's Law, which states that the flux (J) is proportional to the concentration gradient across the membrane and the effective permeability (Pe) of the drug through the membrane.

J=Pe (cd-ca)

where cd = donor concentration and ca = acceptor concentration.

Essentially, the greater the concentration gradient and/or the higher the membrane permeability, the higher the drug flux and the total amount of drug that can be absorbed.

Oral absorption is the process by which a drug is absorbed into the bloodstream after oral administration (ingestion). The drug must pass through various barriers, including the gastrointestinal (GI) tract and intestinal membranes, to reach systemic circulation. Hence, the ability of the drug to permeate biological membranes is crucial as well as the concentration as a drug must dissolve in the gastrointestinal fluids to be absorbed.

Understanding these concepts is essential in the development of pharmaceuticals, as it helps predict and optimize the absorption and efficacy of orally administered drugs. Researchers and pharmaceutical scientists consider these factors during drug design and formulation to enhance bioavailability and therapeutic outcomes. For poorly soluble drugs, the concentration in the gastrointestinal tract may be the rate limiting step for oral absorption and pharmaceutical chemists have many tools for improving a drug compounds solubility through the use of formulation ingredients.

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).

Contact us to see how we can help you with your formulation and pharmaceutical development programs.

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