A quiet analytical research laboratory at night, racks of glass vials along a dim bench.

Efflux Transporters (P-gp)

Some compounds enter intestinal cells and are pumped straight back out. P-glycoprotein and related ABC transporters sit on the lumen-facing surface of enterocytes and export a wide range of substrates, lowering and varying oral absorption and creating drug interaction risks.

How efflux works

P-glycoprotein (ABCB1) is an ATP-driven pump that recognizes many lipophilic, often cationic molecules. In the gut it works with CYP3A4 in the same cells, so a compound pumped out and re-absorbed repeatedly has more chances to be metabolized. Breast cancer resistance protein (ABCG2) and MRP2 add further efflux capacity. Expression varies along the intestine and between people, which contributes to variable exposure. The result is that the same dose can give very different exposure in two people.

Compounds affected

Digoxin is the classic clinical probe substrate. Among natural actives, in vitro and animal studies identify several flavonoids and alkaloids, including berberine, as substrates or modulators. Many polyphenols also inhibit P-gp at high concentrations, which is relevant for interactions with prescription drugs. Regulators require transporter assessment for new drugs because inhibition can raise exposure to co-administered substrates. Much of the natural-product evidence remains preclinical and has not been confirmed in human pharmacokinetic studies.

Formulation responses

Several common excipients inhibit P-gp in vitro, including vitamin E TPGS, polysorbate 80 and certain poloxamers. Lipid systems can also shift absorption toward lymphatic pathways. Deliberate P-gp inhibition must be weighed against interaction risk with medicines the consumer may already take. Most in vitro inhibition data come from concentrations that may not be reached in the human gut, so a formulation effect must be confirmed with a bidirectional transport study and, ultimately, human pharmacokinetics.

Key facts

P-glycoprotein limits oral bioavailability and mediates drug interactions for many substrates (Lin and Yamazaki 2003, Clin Pharmacokinet)
FDA recommends in vitro evaluation of whether investigational drugs are P-gp and BCRP substrates or inhibitors (FDA guidance, ICH M12 Drug Interaction Studies, 2024)
Vitamin E TPGS inhibits P-glycoprotein-mediated efflux in vitro (Dintaman and Silverman 1999, Pharm Res)
Pluronic block copolymers inhibit P-gp by depleting ATP and altering membrane fluidity (Batrakova and Kabanov 2008, J Control Release)

How our delivery technology applies

Encapsulation can change how a substrate meets the transporter. Releasing the active in a concentrated burst at the epithelium can partially saturate P-gp locally, and outer layers can carry excipients with documented in vitro P-gp inhibition. Because systemic P-gp inhibition would affect other medicines, our designs target local effects and are screened for interaction liability, not maximal inhibition.

Ask for a transporter-aware formulation review.