Therapeutic water-soluble polymer-drug conjugates are typically administered via parenteral route mostly by intravenous injections. This is due to the limited absorption of such conjugates from the gastrointestinal (GI) tract as a result of large molecularsize and solubility characteristics of polymeric carriers. Oral bioavailability decreases substantially for molecules of molecular mass greater than 500 700 Da. Furthermore, transport by passive diffusion requires a minimal level of lipophilicity, unless passive absorption occurs via the paracellular route, which is generally limited to small hydrophilic molecules, i.e. 100200 Da. The tight junctions that regulate paracellular transport must be altered to allow the access of polymers and other macromolecules. Surfactants are useful in altering the tight junctions thereby improve the bioavailability of the drugs. Various techniques helpful for enhancement of permeability of polymer drug conjugates were discussed in detail.
Key words: PAMAM Dendrimers, Challenges in oral delivery, Techniques to improve oral bioavailability
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