Lipophilic drug absorption activity

Doxycycline tends to be more active against some bacteria than other tetracyclines. This is probably due to its slower excretion rather than to enhanced oral absorption. Doxycycline is used in cases where cost is unimportant. It is a very lipophilic drug that shows a high bioavailability, being almost completely absorbed after oral administration to different animal species except chickens (250, 251). 

Beside membrane transporters such as PepTl and PepT2, which act as absorptive systems, there are transporters like P-gp and the MRP 15, which transport certain drugs actively back into the intestinal lumen. These efflux pumps are located in several tissues including liver, kidney, brain, and intestine [90,91]. In the intestine, efflux systems are predominantly located at the apical side of the epithelial cells. Lipophilic drugs are usually absorbed by the transcellular route so that they are mostly affected by these systems. Interestingly, the intracellular occurring CYP3A metabolizes compounds to substrates that are eliminated by P-gp [92],... 

A randomised placebo-controlled study in 16 healthy subjects found that orlistat 120 mg three times daily reduced the AUC and peak serum level of a single 1,2-g dose of amiodarone by 23% and 27%, respectively. Levels of its active metabolite, desethylamiodarone, were similarly r ueed. The half-life and time to maximum serum level were not significantly altered. It was suggested that orlistat, which inhibits dietary fat absorption, may also reduce the absorption of amiodarone, which is a lipophilic drug. ... 

Some drug absorption enhancers are capable of loosening tight junctions (zonula occludens) and thereby facilitate paracellular absorption of drug molecules and improve the bioavailability of active pharmaceutical ingredients with low membrane permeability. The penetration enhancers include chelating agents [e.g., ethylenediaminetetraacetic acid), toxins [e.g., zonula occludens toxin), plant-derived materials [e.g., aloe vera gel), and cationic polymers. Polycationic lipophilic-core dendrons, which form lipophilic ion-pairs with heparin, were studied as a system for oral delivery of heparin. ... 

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